[v2,00/15] DRM fbconv helpers for converting fbdev drivers
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Thomas Zimmermann Oct. 14, 2019, 2:04 p.m. UTC
(was: DRM driver for fbdev devices)

This is version 2 of the fbdev conversion helpers. It's more or less a
rewrite of the original patchset.

The fbdev subsystem is considered legacy and will probably be removed at
some point. This would mean the loss of a signifanct number of drivers.
Some of the affected hardware is not in use any longer, but some hardware
is still around and provides good(-enough) framebuffers.

The fbconv helpers allow for running the current DRM stack on top of fbdev
drivers. It's a set of functions that convert between fbdev interfaces and
DRM interfaces. Based on SHMEM and simple KMS helpers, it only offers the
basic functionality of a framebuffer, but should be compatible with most
existing fbdev drivers.

A DRM driver using fbconv helpers consists of

  * DRM stub code that calls into fbconv helpers, and
  * the original fbdev driver code.

The fbdev driver code has to be modified to register itself with the
stub driver instead of the fbdev core framework. A tutorial on how to use
the helpers is part of this patchset. The resulting driver hybrid can be
refactored into a first-class DRM driver. The fbconv helpers contain a
number of comments, labeled 'DRM porting note', which explain the required
steps.

I tested the current patchset with the following drivers: atyfb, aty128fb,
matroxfb, pm2fb, pm3fb, rivafb, s3fb, savagefb, sisfb, tdfxfb and tridentfb.
With each, I was able to successfully start with fbcon enabled, run weston and
X11. The drivers are available at [1]. For reference, the patchset includes
the Matrox stub driver.

v2:
	* rename to fbconv helpers
	* rewrite as helper library
	* switch over to simple KMS helpers
	* switch over to SHMEM
	* add documentation

[1] https://gitlab.freedesktop.org/tzimmermann/linux/commits/fbconv-plus-drivers

Thomas Zimmermann (15):
  fbdev: Export fb_check_foreignness()
  fbdev: Export FBPIXMAPSIZE
  drm/simple-kms-helper: Add mode_fixup() to simple display pipe
  drm: Add fbconv helper module
  drm/fbconv: Add DRM <-> fbdev pixel-format conversion
  drm/fbconv: Add mode conversion DRM <-> fbdev
  drm/fbconv: Add modesetting infrastructure
  drm/fbconv: Add plane-state check and update
  drm/fbconv: Mode-setting pipeline enable / disable
  drm/fbconv: Reimplement several fbdev interfaces
  drm/fbconv: Add helpers for init and cleanup of fb_info structures
  drm/fbconv: Add helper documentation
  staging: Add mgakms driver
  staging/mgakms: Import matroxfb driver source code
  staging/mgakms: Update matroxfb driver code for DRM

 Documentation/gpu/drm-kms-helpers.rst     |   12 +
 Documentation/gpu/todo.rst                |   15 +
 drivers/gpu/drm/Kconfig                   |   11 +
 drivers/gpu/drm/Makefile                  |    1 +
 drivers/gpu/drm/drm_fbconv_helper.c       | 2126 +++++++++++++++++
 drivers/gpu/drm/drm_simple_kms_helper.c   |   15 +
 drivers/staging/Kconfig                   |    2 +
 drivers/staging/Makefile                  |    1 +
 drivers/staging/mgakms/Kconfig            |   18 +
 drivers/staging/mgakms/Makefile           |   17 +
 drivers/staging/mgakms/g450_pll.c         |  539 +++++
 drivers/staging/mgakms/g450_pll.h         |   13 +
 drivers/staging/mgakms/i2c-matroxfb.c     |  238 ++
 drivers/staging/mgakms/matroxfb_DAC1064.c | 1082 +++++++++
 drivers/staging/mgakms/matroxfb_DAC1064.h |  174 ++
 drivers/staging/mgakms/matroxfb_Ti3026.c  |  746 ++++++
 drivers/staging/mgakms/matroxfb_Ti3026.h  |   10 +
 drivers/staging/mgakms/matroxfb_accel.c   |  519 +++++
 drivers/staging/mgakms/matroxfb_accel.h   |    9 +
 drivers/staging/mgakms/matroxfb_base.c    | 2592 +++++++++++++++++++++
 drivers/staging/mgakms/matroxfb_base.h    |  700 ++++++
 drivers/staging/mgakms/matroxfb_crtc2.h   |   35 +
 drivers/staging/mgakms/matroxfb_g450.c    |  640 +++++
 drivers/staging/mgakms/matroxfb_g450.h    |   10 +
 drivers/staging/mgakms/matroxfb_maven.h   |   21 +
 drivers/staging/mgakms/matroxfb_misc.c    |  815 +++++++
 drivers/staging/mgakms/matroxfb_misc.h    |   22 +
 drivers/staging/mgakms/mga_device.c       |   68 +
 drivers/staging/mgakms/mga_device.h       |   30 +
 drivers/staging/mgakms/mga_drv.c          |  129 +
 drivers/staging/mgakms/mga_drv.h          |   14 +
 drivers/video/fbdev/core/fbmem.c          |    5 +-
 include/drm/drm_fbconv_helper.h           |  150 ++
 include/drm/drm_simple_kms_helper.h       |   43 +
 include/linux/fb.h                        |    3 +
 35 files changed, 10822 insertions(+), 3 deletions(-)
 create mode 100644 drivers/gpu/drm/drm_fbconv_helper.c
 create mode 100644 drivers/staging/mgakms/Kconfig
 create mode 100644 drivers/staging/mgakms/Makefile
 create mode 100644 drivers/staging/mgakms/g450_pll.c
 create mode 100644 drivers/staging/mgakms/g450_pll.h
 create mode 100644 drivers/staging/mgakms/i2c-matroxfb.c
 create mode 100644 drivers/staging/mgakms/matroxfb_DAC1064.c
 create mode 100644 drivers/staging/mgakms/matroxfb_DAC1064.h
 create mode 100644 drivers/staging/mgakms/matroxfb_Ti3026.c
 create mode 100644 drivers/staging/mgakms/matroxfb_Ti3026.h
 create mode 100644 drivers/staging/mgakms/matroxfb_accel.c
 create mode 100644 drivers/staging/mgakms/matroxfb_accel.h
 create mode 100644 drivers/staging/mgakms/matroxfb_base.c
 create mode 100644 drivers/staging/mgakms/matroxfb_base.h
 create mode 100644 drivers/staging/mgakms/matroxfb_crtc2.h
 create mode 100644 drivers/staging/mgakms/matroxfb_g450.c
 create mode 100644 drivers/staging/mgakms/matroxfb_g450.h
 create mode 100644 drivers/staging/mgakms/matroxfb_maven.h
 create mode 100644 drivers/staging/mgakms/matroxfb_misc.c
 create mode 100644 drivers/staging/mgakms/matroxfb_misc.h
 create mode 100644 drivers/staging/mgakms/mga_device.c
 create mode 100644 drivers/staging/mgakms/mga_device.h
 create mode 100644 drivers/staging/mgakms/mga_drv.c
 create mode 100644 drivers/staging/mgakms/mga_drv.h
 create mode 100644 include/drm/drm_fbconv_helper.h

--
2.23.0

Comments

Sam Ravnborg Oct. 14, 2019, 8:36 p.m. UTC | #1
Hi Thomas.

On Mon, Oct 14, 2019 at 04:04:01PM +0200, Thomas Zimmermann wrote:
> (was: DRM driver for fbdev devices)
> 
> This is version 2 of the fbdev conversion helpers. It's more or less a
> rewrite of the original patchset.
> 
> The fbdev subsystem is considered legacy and will probably be removed at
> some point. This would mean the loss of a signifanct number of drivers.
> Some of the affected hardware is not in use any longer, but some hardware
> is still around and provides good(-enough) framebuffers.
> 
> The fbconv helpers allow for running the current DRM stack on top of fbdev
> drivers. It's a set of functions that convert between fbdev interfaces and
> DRM interfaces. Based on SHMEM and simple KMS helpers, it only offers the
> basic functionality of a framebuffer, but should be compatible with most
> existing fbdev drivers.
> 
> A DRM driver using fbconv helpers consists of
> 
>   * DRM stub code that calls into fbconv helpers, and
>   * the original fbdev driver code.
> 
> The fbdev driver code has to be modified to register itself with the
> stub driver instead of the fbdev core framework. A tutorial on how to use
> the helpers is part of this patchset. The resulting driver hybrid can be
> refactored into a first-class DRM driver. The fbconv helpers contain a
> number of comments, labeled 'DRM porting note', which explain the required
> steps.
> 
> I tested the current patchset with the following drivers: atyfb, aty128fb,
> matroxfb, pm2fb, pm3fb, rivafb, s3fb, savagefb, sisfb, tdfxfb and tridentfb.
> With each, I was able to successfully start with fbcon enabled, run weston and
> X11. The drivers are available at [1]. For reference, the patchset includes
> the Matrox stub driver.

In general I like the idea of modernizing the existing fbdev drivers.
What I fail to read in your intro above is if this allows us to phase
out the migrated fbdev drivers sooner?
Or do we end up with two drivers to maintain?

Obviously a full migration to a DRM driver was preferred - but this may
serve as a step in that direction.
But we should not end up with two drivers doing almost the same.

Another general question. Do we want the modernized DRM drivers to end
up in staging? Why should they not go direct into drm/*
I know they are not fully atomic but this is not new drivers so maybe
they can be excused.
Problem is that drm drivers in staging live a secret nonvisible life
where they are easy to forget when we change interfaces and such.

	Sam
Thomas Zimmermann Oct. 15, 2019, 6:11 a.m. UTC | #2
Hi

Am 14.10.19 um 22:36 schrieb Sam Ravnborg:
> Hi Thomas.
> 
> On Mon, Oct 14, 2019 at 04:04:01PM +0200, Thomas Zimmermann wrote:
>> (was: DRM driver for fbdev devices)
>>
>> This is version 2 of the fbdev conversion helpers. It's more or less a
>> rewrite of the original patchset.
>>
>> The fbdev subsystem is considered legacy and will probably be removed at
>> some point. This would mean the loss of a signifanct number of drivers.
>> Some of the affected hardware is not in use any longer, but some hardware
>> is still around and provides good(-enough) framebuffers.
>>
>> The fbconv helpers allow for running the current DRM stack on top of fbdev
>> drivers. It's a set of functions that convert between fbdev interfaces and
>> DRM interfaces. Based on SHMEM and simple KMS helpers, it only offers the
>> basic functionality of a framebuffer, but should be compatible with most
>> existing fbdev drivers.
>>
>> A DRM driver using fbconv helpers consists of
>>
>>    * DRM stub code that calls into fbconv helpers, and
>>    * the original fbdev driver code.
>>
>> The fbdev driver code has to be modified to register itself with the
>> stub driver instead of the fbdev core framework. A tutorial on how to use
>> the helpers is part of this patchset. The resulting driver hybrid can be
>> refactored into a first-class DRM driver. The fbconv helpers contain a
>> number of comments, labeled 'DRM porting note', which explain the required
>> steps.
>>
>> I tested the current patchset with the following drivers: atyfb, aty128fb,
>> matroxfb, pm2fb, pm3fb, rivafb, s3fb, savagefb, sisfb, tdfxfb and tridentfb.
>> With each, I was able to successfully start with fbcon enabled, run weston and
>> X11. The drivers are available at [1]. For reference, the patchset includes
>> the Matrox stub driver.
> 
> In general I like the idea of modernizing the existing fbdev drivers.
> What I fail to read in your intro above is if this allows us to phase
> out the migrated fbdev drivers sooner?
> Or do we end up with two drivers to maintain?

The idea is that an fbdev driver is converted over to DRM and, once 
ready, the original fbdev driver gets removed. When a hybrid driver gets 
added, I'd want to see the rsp developer actually clean up and refactor 
the code. There shouldn't be multiple drivers for long.

But most of the fbdev drivers appear to be unmaintained anyway. I 
wouldn't expect having two drivers for a few releases would make much of 
a difference.

> Obviously a full migration to a DRM driver was preferred - but this may
> serve as a step in that direction.
> But we should not end up with two drivers doing almost the same.
> 
> Another general question. Do we want the modernized DRM drivers to end
> up in staging? Why should they not go direct into drm/*
> I know they are not fully atomic but this is not new drivers so maybe
> they can be excused.
> Problem is that drm drivers in staging live a secret nonvisible life
> where they are easy to forget when we change interfaces and such.

True. OTOH putting them next to the regular DRM code sends the message 
that the driver is already complete and in good shape. Those hybrid 
drivers are limited in functionality and don't really live up to 
anyone's requirements for code quality. It's the kind of code one would 
expect in staging.

Best regards
Thomas

> 	Sam
> _______________________________________________
> dri-devel mailing list
> dri-devel@lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/dri-devel
>
Daniel Vetter Oct. 15, 2019, 2:33 p.m. UTC | #3
Hi Thomas,

On Mon, Oct 14, 2019 at 04:04:01PM +0200, Thomas Zimmermann wrote:
> (was: DRM driver for fbdev devices)
> 
> This is version 2 of the fbdev conversion helpers. It's more or less a
> rewrite of the original patchset.
> 
> The fbdev subsystem is considered legacy and will probably be removed at
> some point. This would mean the loss of a signifanct number of drivers.
> Some of the affected hardware is not in use any longer, but some hardware
> is still around and provides good(-enough) framebuffers.
> 
> The fbconv helpers allow for running the current DRM stack on top of fbdev
> drivers. It's a set of functions that convert between fbdev interfaces and
> DRM interfaces. Based on SHMEM and simple KMS helpers, it only offers the
> basic functionality of a framebuffer, but should be compatible with most
> existing fbdev drivers.
> 
> A DRM driver using fbconv helpers consists of
> 
>   * DRM stub code that calls into fbconv helpers, and
>   * the original fbdev driver code.
> 
> The fbdev driver code has to be modified to register itself with the
> stub driver instead of the fbdev core framework. A tutorial on how to use
> the helpers is part of this patchset. The resulting driver hybrid can be
> refactored into a first-class DRM driver. The fbconv helpers contain a
> number of comments, labeled 'DRM porting note', which explain the required
> steps.
> 
> I tested the current patchset with the following drivers: atyfb, aty128fb,
> matroxfb, pm2fb, pm3fb, rivafb, s3fb, savagefb, sisfb, tdfxfb and tridentfb.
> With each, I was able to successfully start with fbcon enabled, run weston and
> X11. The drivers are available at [1]. For reference, the patchset includes
> the Matrox stub driver.

So I really don't want to rain on the parade here, since if you think this
is useful when converting fbdev drivers I'll buy that, and I'm all for
getting more modern drivers into drm.

But I have a bunch of concerns with the approach you're proposing here:

- we've tried staging for drm driver refactoring, it hurts. Separate tree
  plus the quick pace in refactoring create lots of pains. And for small
  drivers refacotoring before it's not buying you anything above
  refactoring in your own personal tree. And for big drivers we're fairly
  lenient with merging drivers that aren't fully polished yet, if there's
  a team serious enough with cleaning up the mess. I think even merging
  partial drivers directly under drivers/gpu (but behind CONFIG_BROKEN) is
  better than staging.

- we've had conversion helpers before (for the legacy kms -> atomic
  upgrade). They constantly broke, pretty much every release when someone
  wanted to use them they first had to fix them up again. I think having
  those helpers is good, but better to just have them in some branch
  somewhere where it's clear that they might not work anymore on latest
  upstream.

- especially for some of these simple fbdev drivers I feel like just
  typing a new driver from scratch might be simpler.

A few more concerns specifically for your mga example:

- We already have a mga driver. Might be better to integrate support for
  older mgas into that than have a parallel driver.

- Your helper is based on simple display pipe, and I think for these old
  mga chips (especially the dual pipe mga 450 and 550) simple display pipe
  helper is more a hindering detour than actual help. From a quick read
  through the code (especially all the custom ioctls) you definitely want
  separate TV-out connector to expose all the tv mode properties (instead
  of the custom ioctls).

- On the topic of ioctls, looks like we could add FBIOGET_VBLANK to our
  generic implementation in the fbdev helpers.

So here's my alternative proposal:

- You push this as a branch onto a gitlab repo (freedesktop.org or
  wherever you feel like).

- You add a gitlab CI target to autobuild the very nice kerneldoc you've
  created. Feel free to also do this with anything else you're familiar
  with, it's just I know gitlab and it's real simple to get a few docs
  autogenerated and published with it.

- We add a todo.rst patch linking to your branch and the docs and a few
  lines on how to best convert an fbdev driver over to kms/atomic.

And all the drivers would land the usual way, like any of the other
drivers we've added to drivers/gpu/drm over the past few years.

Thoughts?

Cheers, Daniel
> 
> v2:
> 	* rename to fbconv helpers
> 	* rewrite as helper library
> 	* switch over to simple KMS helpers
> 	* switch over to SHMEM
> 	* add documentation
> 
> [1] https://gitlab.freedesktop.org/tzimmermann/linux/commits/fbconv-plus-drivers
> 
> Thomas Zimmermann (15):
>   fbdev: Export fb_check_foreignness()
>   fbdev: Export FBPIXMAPSIZE
>   drm/simple-kms-helper: Add mode_fixup() to simple display pipe
>   drm: Add fbconv helper module
>   drm/fbconv: Add DRM <-> fbdev pixel-format conversion
>   drm/fbconv: Add mode conversion DRM <-> fbdev
>   drm/fbconv: Add modesetting infrastructure
>   drm/fbconv: Add plane-state check and update
>   drm/fbconv: Mode-setting pipeline enable / disable
>   drm/fbconv: Reimplement several fbdev interfaces
>   drm/fbconv: Add helpers for init and cleanup of fb_info structures
>   drm/fbconv: Add helper documentation
>   staging: Add mgakms driver
>   staging/mgakms: Import matroxfb driver source code
>   staging/mgakms: Update matroxfb driver code for DRM
> 
>  Documentation/gpu/drm-kms-helpers.rst     |   12 +
>  Documentation/gpu/todo.rst                |   15 +
>  drivers/gpu/drm/Kconfig                   |   11 +
>  drivers/gpu/drm/Makefile                  |    1 +
>  drivers/gpu/drm/drm_fbconv_helper.c       | 2126 +++++++++++++++++
>  drivers/gpu/drm/drm_simple_kms_helper.c   |   15 +
>  drivers/staging/Kconfig                   |    2 +
>  drivers/staging/Makefile                  |    1 +
>  drivers/staging/mgakms/Kconfig            |   18 +
>  drivers/staging/mgakms/Makefile           |   17 +
>  drivers/staging/mgakms/g450_pll.c         |  539 +++++
>  drivers/staging/mgakms/g450_pll.h         |   13 +
>  drivers/staging/mgakms/i2c-matroxfb.c     |  238 ++
>  drivers/staging/mgakms/matroxfb_DAC1064.c | 1082 +++++++++
>  drivers/staging/mgakms/matroxfb_DAC1064.h |  174 ++
>  drivers/staging/mgakms/matroxfb_Ti3026.c  |  746 ++++++
>  drivers/staging/mgakms/matroxfb_Ti3026.h  |   10 +
>  drivers/staging/mgakms/matroxfb_accel.c   |  519 +++++
>  drivers/staging/mgakms/matroxfb_accel.h   |    9 +
>  drivers/staging/mgakms/matroxfb_base.c    | 2592 +++++++++++++++++++++
>  drivers/staging/mgakms/matroxfb_base.h    |  700 ++++++
>  drivers/staging/mgakms/matroxfb_crtc2.h   |   35 +
>  drivers/staging/mgakms/matroxfb_g450.c    |  640 +++++
>  drivers/staging/mgakms/matroxfb_g450.h    |   10 +
>  drivers/staging/mgakms/matroxfb_maven.h   |   21 +
>  drivers/staging/mgakms/matroxfb_misc.c    |  815 +++++++
>  drivers/staging/mgakms/matroxfb_misc.h    |   22 +
>  drivers/staging/mgakms/mga_device.c       |   68 +
>  drivers/staging/mgakms/mga_device.h       |   30 +
>  drivers/staging/mgakms/mga_drv.c          |  129 +
>  drivers/staging/mgakms/mga_drv.h          |   14 +
>  drivers/video/fbdev/core/fbmem.c          |    5 +-
>  include/drm/drm_fbconv_helper.h           |  150 ++
>  include/drm/drm_simple_kms_helper.h       |   43 +
>  include/linux/fb.h                        |    3 +
>  35 files changed, 10822 insertions(+), 3 deletions(-)
>  create mode 100644 drivers/gpu/drm/drm_fbconv_helper.c
>  create mode 100644 drivers/staging/mgakms/Kconfig
>  create mode 100644 drivers/staging/mgakms/Makefile
>  create mode 100644 drivers/staging/mgakms/g450_pll.c
>  create mode 100644 drivers/staging/mgakms/g450_pll.h
>  create mode 100644 drivers/staging/mgakms/i2c-matroxfb.c
>  create mode 100644 drivers/staging/mgakms/matroxfb_DAC1064.c
>  create mode 100644 drivers/staging/mgakms/matroxfb_DAC1064.h
>  create mode 100644 drivers/staging/mgakms/matroxfb_Ti3026.c
>  create mode 100644 drivers/staging/mgakms/matroxfb_Ti3026.h
>  create mode 100644 drivers/staging/mgakms/matroxfb_accel.c
>  create mode 100644 drivers/staging/mgakms/matroxfb_accel.h
>  create mode 100644 drivers/staging/mgakms/matroxfb_base.c
>  create mode 100644 drivers/staging/mgakms/matroxfb_base.h
>  create mode 100644 drivers/staging/mgakms/matroxfb_crtc2.h
>  create mode 100644 drivers/staging/mgakms/matroxfb_g450.c
>  create mode 100644 drivers/staging/mgakms/matroxfb_g450.h
>  create mode 100644 drivers/staging/mgakms/matroxfb_maven.h
>  create mode 100644 drivers/staging/mgakms/matroxfb_misc.c
>  create mode 100644 drivers/staging/mgakms/matroxfb_misc.h
>  create mode 100644 drivers/staging/mgakms/mga_device.c
>  create mode 100644 drivers/staging/mgakms/mga_device.h
>  create mode 100644 drivers/staging/mgakms/mga_drv.c
>  create mode 100644 drivers/staging/mgakms/mga_drv.h
>  create mode 100644 include/drm/drm_fbconv_helper.h
> 
> --
> 2.23.0
>
Thomas Zimmermann Oct. 15, 2019, 5:28 p.m. UTC | #4
Hi Daniel

Am 15.10.19 um 16:33 schrieb Daniel Vetter:
> Hi Thomas,
> 
> On Mon, Oct 14, 2019 at 04:04:01PM +0200, Thomas Zimmermann wrote:
>> (was: DRM driver for fbdev devices)
>>
>> This is version 2 of the fbdev conversion helpers. It's more or less a
>> rewrite of the original patchset.
>>
>> The fbdev subsystem is considered legacy and will probably be removed at
>> some point. This would mean the loss of a signifanct number of drivers.
>> Some of the affected hardware is not in use any longer, but some hardware
>> is still around and provides good(-enough) framebuffers.
>>
>> The fbconv helpers allow for running the current DRM stack on top of fbdev
>> drivers. It's a set of functions that convert between fbdev interfaces and
>> DRM interfaces. Based on SHMEM and simple KMS helpers, it only offers the
>> basic functionality of a framebuffer, but should be compatible with most
>> existing fbdev drivers.
>>
>> A DRM driver using fbconv helpers consists of
>>
>>   * DRM stub code that calls into fbconv helpers, and
>>   * the original fbdev driver code.
>>
>> The fbdev driver code has to be modified to register itself with the
>> stub driver instead of the fbdev core framework. A tutorial on how to use
>> the helpers is part of this patchset. The resulting driver hybrid can be
>> refactored into a first-class DRM driver. The fbconv helpers contain a
>> number of comments, labeled 'DRM porting note', which explain the required
>> steps.
>>
>> I tested the current patchset with the following drivers: atyfb, aty128fb,
>> matroxfb, pm2fb, pm3fb, rivafb, s3fb, savagefb, sisfb, tdfxfb and tridentfb.
>> With each, I was able to successfully start with fbcon enabled, run weston and
>> X11. The drivers are available at [1]. For reference, the patchset includes
>> the Matrox stub driver.
> 
> So I really don't want to rain on the parade here, since if you think this
> is useful when converting fbdev drivers I'll buy that, and I'm all for
> getting more modern drivers into drm.
> 
> But I have a bunch of concerns with the approach you're proposing here:
> 
> - we've tried staging for drm driver refactoring, it hurts. Separate tree
>   plus the quick pace in refactoring create lots of pains. And for small
>   drivers refacotoring before it's not buying you anything above
>   refactoring in your own personal tree. And for big drivers we're fairly
>   lenient with merging drivers that aren't fully polished yet, if there's
>   a team serious enough with cleaning up the mess. I think even merging
>   partial drivers directly under drivers/gpu (but behind CONFIG_BROKEN) is
>   better than staging.

I mostly put this into staging, because it's the kind of code you'd
expect there.

> - we've had conversion helpers before (for the legacy kms -> atomic
>   upgrade). They constantly broke, pretty much every release when someone
>   wanted to use them they first had to fix them up again. I think having
>   those helpers is good, but better to just have them in some branch
>   somewhere where it's clear that they might not work anymore on latest
>   upstream.
> 
> - especially for some of these simple fbdev drivers I feel like just
>   typing a new driver from scratch might be simpler.
> 
> A few more concerns specifically for your mga example:
> 
> - We already have a mga driver. Might be better to integrate support for
>   older mgas into that than have a parallel driver.

Two colleagues of mine, Takashi and Egbert, send a patch that added
support for desktop G200s to mgag200. [1] But it was rejected because
the devices are two old and not relevant any longer. If that opinion has
changed in the meantime, I wouldn't mind adding support for desktop GPUs
to the driver.

> - Your helper is based on simple display pipe, and I think for these old
>   mga chips (especially the dual pipe mga 450 and 550) simple display pipe
>   helper is more a hindering detour than actual help. From a quick read
>   through the code (especially all the custom ioctls) you definitely want
>   separate TV-out connector to expose all the tv mode properties (instead
>   of the custom ioctls).

Around the G100, there's something like a change in generation. Before,
devices had only a single output and less than 8 MiB of RAM. This works
well with GEM SHMEM and simple KMS. Afterwards, devices have 8 MiB or
more and multiple outputs. GEM VRAM and the full set of helpers fit this
much better. Maybe having 2 drivers that share common code (or 3 with
the Server Engine chipsets) makes most sense.

> 
> - On the topic of ioctls, looks like we could add FBIOGET_VBLANK to our
>   generic implementation in the fbdev helpers.
> 
> So here's my alternative proposal:
> 
> - You push this as a branch onto a gitlab repo (freedesktop.org or
>   wherever you feel like).
> 
> - You add a gitlab CI target to autobuild the very nice kerneldoc you've
>   created. Feel free to also do this with anything else you're familiar
>   with, it's just I know gitlab and it's real simple to get a few docs
>   autogenerated and published with it.
> 
> - We add a todo.rst patch linking to your branch and the docs and a few
>   lines on how to best convert an fbdev driver over to kms/atomic.

Yes we can do that.

Best regards
Thomas

[1] https://lists.freedesktop.org/archives/dri-devel/2017-July/147868.html

> 
> And all the drivers would land the usual way, like any of the other
> drivers we've added to drivers/gpu/drm over the past few years.
> 
> Thoughts?
> 
> Cheers, Daniel
>>
>> v2:
>> 	* rename to fbconv helpers
>> 	* rewrite as helper library
>> 	* switch over to simple KMS helpers
>> 	* switch over to SHMEM
>> 	* add documentation
>>
>> [1] https://gitlab.freedesktop.org/tzimmermann/linux/commits/fbconv-plus-drivers
>>
>> Thomas Zimmermann (15):
>>   fbdev: Export fb_check_foreignness()
>>   fbdev: Export FBPIXMAPSIZE
>>   drm/simple-kms-helper: Add mode_fixup() to simple display pipe
>>   drm: Add fbconv helper module
>>   drm/fbconv: Add DRM <-> fbdev pixel-format conversion
>>   drm/fbconv: Add mode conversion DRM <-> fbdev
>>   drm/fbconv: Add modesetting infrastructure
>>   drm/fbconv: Add plane-state check and update
>>   drm/fbconv: Mode-setting pipeline enable / disable
>>   drm/fbconv: Reimplement several fbdev interfaces
>>   drm/fbconv: Add helpers for init and cleanup of fb_info structures
>>   drm/fbconv: Add helper documentation
>>   staging: Add mgakms driver
>>   staging/mgakms: Import matroxfb driver source code
>>   staging/mgakms: Update matroxfb driver code for DRM
>>
>>  Documentation/gpu/drm-kms-helpers.rst     |   12 +
>>  Documentation/gpu/todo.rst                |   15 +
>>  drivers/gpu/drm/Kconfig                   |   11 +
>>  drivers/gpu/drm/Makefile                  |    1 +
>>  drivers/gpu/drm/drm_fbconv_helper.c       | 2126 +++++++++++++++++
>>  drivers/gpu/drm/drm_simple_kms_helper.c   |   15 +
>>  drivers/staging/Kconfig                   |    2 +
>>  drivers/staging/Makefile                  |    1 +
>>  drivers/staging/mgakms/Kconfig            |   18 +
>>  drivers/staging/mgakms/Makefile           |   17 +
>>  drivers/staging/mgakms/g450_pll.c         |  539 +++++
>>  drivers/staging/mgakms/g450_pll.h         |   13 +
>>  drivers/staging/mgakms/i2c-matroxfb.c     |  238 ++
>>  drivers/staging/mgakms/matroxfb_DAC1064.c | 1082 +++++++++
>>  drivers/staging/mgakms/matroxfb_DAC1064.h |  174 ++
>>  drivers/staging/mgakms/matroxfb_Ti3026.c  |  746 ++++++
>>  drivers/staging/mgakms/matroxfb_Ti3026.h  |   10 +
>>  drivers/staging/mgakms/matroxfb_accel.c   |  519 +++++
>>  drivers/staging/mgakms/matroxfb_accel.h   |    9 +
>>  drivers/staging/mgakms/matroxfb_base.c    | 2592 +++++++++++++++++++++
>>  drivers/staging/mgakms/matroxfb_base.h    |  700 ++++++
>>  drivers/staging/mgakms/matroxfb_crtc2.h   |   35 +
>>  drivers/staging/mgakms/matroxfb_g450.c    |  640 +++++
>>  drivers/staging/mgakms/matroxfb_g450.h    |   10 +
>>  drivers/staging/mgakms/matroxfb_maven.h   |   21 +
>>  drivers/staging/mgakms/matroxfb_misc.c    |  815 +++++++
>>  drivers/staging/mgakms/matroxfb_misc.h    |   22 +
>>  drivers/staging/mgakms/mga_device.c       |   68 +
>>  drivers/staging/mgakms/mga_device.h       |   30 +
>>  drivers/staging/mgakms/mga_drv.c          |  129 +
>>  drivers/staging/mgakms/mga_drv.h          |   14 +
>>  drivers/video/fbdev/core/fbmem.c          |    5 +-
>>  include/drm/drm_fbconv_helper.h           |  150 ++
>>  include/drm/drm_simple_kms_helper.h       |   43 +
>>  include/linux/fb.h                        |    3 +
>>  35 files changed, 10822 insertions(+), 3 deletions(-)
>>  create mode 100644 drivers/gpu/drm/drm_fbconv_helper.c
>>  create mode 100644 drivers/staging/mgakms/Kconfig
>>  create mode 100644 drivers/staging/mgakms/Makefile
>>  create mode 100644 drivers/staging/mgakms/g450_pll.c
>>  create mode 100644 drivers/staging/mgakms/g450_pll.h
>>  create mode 100644 drivers/staging/mgakms/i2c-matroxfb.c
>>  create mode 100644 drivers/staging/mgakms/matroxfb_DAC1064.c
>>  create mode 100644 drivers/staging/mgakms/matroxfb_DAC1064.h
>>  create mode 100644 drivers/staging/mgakms/matroxfb_Ti3026.c
>>  create mode 100644 drivers/staging/mgakms/matroxfb_Ti3026.h
>>  create mode 100644 drivers/staging/mgakms/matroxfb_accel.c
>>  create mode 100644 drivers/staging/mgakms/matroxfb_accel.h
>>  create mode 100644 drivers/staging/mgakms/matroxfb_base.c
>>  create mode 100644 drivers/staging/mgakms/matroxfb_base.h
>>  create mode 100644 drivers/staging/mgakms/matroxfb_crtc2.h
>>  create mode 100644 drivers/staging/mgakms/matroxfb_g450.c
>>  create mode 100644 drivers/staging/mgakms/matroxfb_g450.h
>>  create mode 100644 drivers/staging/mgakms/matroxfb_maven.h
>>  create mode 100644 drivers/staging/mgakms/matroxfb_misc.c
>>  create mode 100644 drivers/staging/mgakms/matroxfb_misc.h
>>  create mode 100644 drivers/staging/mgakms/mga_device.c
>>  create mode 100644 drivers/staging/mgakms/mga_device.h
>>  create mode 100644 drivers/staging/mgakms/mga_drv.c
>>  create mode 100644 drivers/staging/mgakms/mga_drv.h
>>  create mode 100644 include/drm/drm_fbconv_helper.h
>>
>> --
>> 2.23.0
>>
>
Daniel Vetter Oct. 15, 2019, 5:48 p.m. UTC | #5
On Tue, Oct 15, 2019 at 7:28 PM Thomas Zimmermann <tzimmermann@suse.de> wrote:
>
> Hi Daniel
>
> Am 15.10.19 um 16:33 schrieb Daniel Vetter:
> > Hi Thomas,
> >
> > On Mon, Oct 14, 2019 at 04:04:01PM +0200, Thomas Zimmermann wrote:
> >> (was: DRM driver for fbdev devices)
> >>
> >> This is version 2 of the fbdev conversion helpers. It's more or less a
> >> rewrite of the original patchset.
> >>
> >> The fbdev subsystem is considered legacy and will probably be removed at
> >> some point. This would mean the loss of a signifanct number of drivers.
> >> Some of the affected hardware is not in use any longer, but some hardware
> >> is still around and provides good(-enough) framebuffers.
> >>
> >> The fbconv helpers allow for running the current DRM stack on top of fbdev
> >> drivers. It's a set of functions that convert between fbdev interfaces and
> >> DRM interfaces. Based on SHMEM and simple KMS helpers, it only offers the
> >> basic functionality of a framebuffer, but should be compatible with most
> >> existing fbdev drivers.
> >>
> >> A DRM driver using fbconv helpers consists of
> >>
> >>   * DRM stub code that calls into fbconv helpers, and
> >>   * the original fbdev driver code.
> >>
> >> The fbdev driver code has to be modified to register itself with the
> >> stub driver instead of the fbdev core framework. A tutorial on how to use
> >> the helpers is part of this patchset. The resulting driver hybrid can be
> >> refactored into a first-class DRM driver. The fbconv helpers contain a
> >> number of comments, labeled 'DRM porting note', which explain the required
> >> steps.
> >>
> >> I tested the current patchset with the following drivers: atyfb, aty128fb,
> >> matroxfb, pm2fb, pm3fb, rivafb, s3fb, savagefb, sisfb, tdfxfb and tridentfb.
> >> With each, I was able to successfully start with fbcon enabled, run weston and
> >> X11. The drivers are available at [1]. For reference, the patchset includes
> >> the Matrox stub driver.
> >
> > So I really don't want to rain on the parade here, since if you think this
> > is useful when converting fbdev drivers I'll buy that, and I'm all for
> > getting more modern drivers into drm.
> >
> > But I have a bunch of concerns with the approach you're proposing here:
> >
> > - we've tried staging for drm driver refactoring, it hurts. Separate tree
> >   plus the quick pace in refactoring create lots of pains. And for small
> >   drivers refacotoring before it's not buying you anything above
> >   refactoring in your own personal tree. And for big drivers we're fairly
> >   lenient with merging drivers that aren't fully polished yet, if there's
> >   a team serious enough with cleaning up the mess. I think even merging
> >   partial drivers directly under drivers/gpu (but behind CONFIG_BROKEN) is
> >   better than staging.
>
> I mostly put this into staging, because it's the kind of code you'd
> expect there.

Yeah, except we tried, it's a real pain. Conclusion by everyone
involved is that staging doesn't work for the drm subsystem.

> > - we've had conversion helpers before (for the legacy kms -> atomic
> >   upgrade). They constantly broke, pretty much every release when someone
> >   wanted to use them they first had to fix them up again. I think having
> >   those helpers is good, but better to just have them in some branch
> >   somewhere where it's clear that they might not work anymore on latest
> >   upstream.
> >
> > - especially for some of these simple fbdev drivers I feel like just
> >   typing a new driver from scratch might be simpler.
> >
> > A few more concerns specifically for your mga example:
> >
> > - We already have a mga driver. Might be better to integrate support for
> >   older mgas into that than have a parallel driver.
>
> Two colleagues of mine, Takashi and Egbert, send a patch that added
> support for desktop G200s to mgag200. [1] But it was rejected because
> the devices are two old and not relevant any longer. If that opinion has
> changed in the meantime, I wouldn't mind adding support for desktop GPUs
> to the driver.

Hm that seems to have petered out inconclusive. I definitely think a
merged mga driver is better than 2 drm atomic kms drivers for roughly
the same hardware. I'm also assuming that at least for now no one
plans to resurrect the 3d acceleration support for these old chips.
But even then it's fairly easy to disable all that on the server
chips.

> > - Your helper is based on simple display pipe, and I think for these old
> >   mga chips (especially the dual pipe mga 450 and 550) simple display pipe
> >   helper is more a hindering detour than actual help. From a quick read
> >   through the code (especially all the custom ioctls) you definitely want
> >   separate TV-out connector to expose all the tv mode properties (instead
> >   of the custom ioctls).
>
> Around the G100, there's something like a change in generation. Before,
> devices had only a single output and less than 8 MiB of RAM. This works
> well with GEM SHMEM and simple KMS. Afterwards, devices have 8 MiB or
> more and multiple outputs. GEM VRAM and the full set of helpers fit this
> much better. Maybe having 2 drivers that share common code (or 3 with
> the Server Engine chipsets) makes most sense.

Yeah if that's the case maybe a mga100 and mga200g driver fits better.
Former based on simple display pipe.

You could also have them in one directory/kernel module, if there's
some low-level functions worth sharing (like clock programming), with
the low level driver probe either setting up the simple display based
mga100 support, or the fancier mga200 support using atomic directly.
If there's really no shared code at all, then separate kernel modules
sounds better.

> > - On the topic of ioctls, looks like we could add FBIOGET_VBLANK to our
> >   generic implementation in the fbdev helpers.
> >
> > So here's my alternative proposal:
> >
> > - You push this as a branch onto a gitlab repo (freedesktop.org or
> >   wherever you feel like).
> >
> > - You add a gitlab CI target to autobuild the very nice kerneldoc you've
> >   created. Feel free to also do this with anything else you're familiar
> >   with, it's just I know gitlab and it's real simple to get a few docs
> >   autogenerated and published with it.
> >
> > - We add a todo.rst patch linking to your branch and the docs and a few
> >   lines on how to best convert an fbdev driver over to kms/atomic.
>
> Yes we can do that.

Sounds like we have a rough plan?
-Daniel

>
> Best regards
> Thomas
>
> [1] https://lists.freedesktop.org/archives/dri-devel/2017-July/147868.html
>
> >
> > And all the drivers would land the usual way, like any of the other
> > drivers we've added to drivers/gpu/drm over the past few years.
> >
> > Thoughts?
> >
> > Cheers, Daniel
> >>
> >> v2:
> >>      * rename to fbconv helpers
> >>      * rewrite as helper library
> >>      * switch over to simple KMS helpers
> >>      * switch over to SHMEM
> >>      * add documentation
> >>
> >> [1] https://gitlab.freedesktop.org/tzimmermann/linux/commits/fbconv-plus-drivers
> >>
> >> Thomas Zimmermann (15):
> >>   fbdev: Export fb_check_foreignness()
> >>   fbdev: Export FBPIXMAPSIZE
> >>   drm/simple-kms-helper: Add mode_fixup() to simple display pipe
> >>   drm: Add fbconv helper module
> >>   drm/fbconv: Add DRM <-> fbdev pixel-format conversion
> >>   drm/fbconv: Add mode conversion DRM <-> fbdev
> >>   drm/fbconv: Add modesetting infrastructure
> >>   drm/fbconv: Add plane-state check and update
> >>   drm/fbconv: Mode-setting pipeline enable / disable
> >>   drm/fbconv: Reimplement several fbdev interfaces
> >>   drm/fbconv: Add helpers for init and cleanup of fb_info structures
> >>   drm/fbconv: Add helper documentation
> >>   staging: Add mgakms driver
> >>   staging/mgakms: Import matroxfb driver source code
> >>   staging/mgakms: Update matroxfb driver code for DRM
> >>
> >>  Documentation/gpu/drm-kms-helpers.rst     |   12 +
> >>  Documentation/gpu/todo.rst                |   15 +
> >>  drivers/gpu/drm/Kconfig                   |   11 +
> >>  drivers/gpu/drm/Makefile                  |    1 +
> >>  drivers/gpu/drm/drm_fbconv_helper.c       | 2126 +++++++++++++++++
> >>  drivers/gpu/drm/drm_simple_kms_helper.c   |   15 +
> >>  drivers/staging/Kconfig                   |    2 +
> >>  drivers/staging/Makefile                  |    1 +
> >>  drivers/staging/mgakms/Kconfig            |   18 +
> >>  drivers/staging/mgakms/Makefile           |   17 +
> >>  drivers/staging/mgakms/g450_pll.c         |  539 +++++
> >>  drivers/staging/mgakms/g450_pll.h         |   13 +
> >>  drivers/staging/mgakms/i2c-matroxfb.c     |  238 ++
> >>  drivers/staging/mgakms/matroxfb_DAC1064.c | 1082 +++++++++
> >>  drivers/staging/mgakms/matroxfb_DAC1064.h |  174 ++
> >>  drivers/staging/mgakms/matroxfb_Ti3026.c  |  746 ++++++
> >>  drivers/staging/mgakms/matroxfb_Ti3026.h  |   10 +
> >>  drivers/staging/mgakms/matroxfb_accel.c   |  519 +++++
> >>  drivers/staging/mgakms/matroxfb_accel.h   |    9 +
> >>  drivers/staging/mgakms/matroxfb_base.c    | 2592 +++++++++++++++++++++
> >>  drivers/staging/mgakms/matroxfb_base.h    |  700 ++++++
> >>  drivers/staging/mgakms/matroxfb_crtc2.h   |   35 +
> >>  drivers/staging/mgakms/matroxfb_g450.c    |  640 +++++
> >>  drivers/staging/mgakms/matroxfb_g450.h    |   10 +
> >>  drivers/staging/mgakms/matroxfb_maven.h   |   21 +
> >>  drivers/staging/mgakms/matroxfb_misc.c    |  815 +++++++
> >>  drivers/staging/mgakms/matroxfb_misc.h    |   22 +
> >>  drivers/staging/mgakms/mga_device.c       |   68 +
> >>  drivers/staging/mgakms/mga_device.h       |   30 +
> >>  drivers/staging/mgakms/mga_drv.c          |  129 +
> >>  drivers/staging/mgakms/mga_drv.h          |   14 +
> >>  drivers/video/fbdev/core/fbmem.c          |    5 +-
> >>  include/drm/drm_fbconv_helper.h           |  150 ++
> >>  include/drm/drm_simple_kms_helper.h       |   43 +
> >>  include/linux/fb.h                        |    3 +
> >>  35 files changed, 10822 insertions(+), 3 deletions(-)
> >>  create mode 100644 drivers/gpu/drm/drm_fbconv_helper.c
> >>  create mode 100644 drivers/staging/mgakms/Kconfig
> >>  create mode 100644 drivers/staging/mgakms/Makefile
> >>  create mode 100644 drivers/staging/mgakms/g450_pll.c
> >>  create mode 100644 drivers/staging/mgakms/g450_pll.h
> >>  create mode 100644 drivers/staging/mgakms/i2c-matroxfb.c
> >>  create mode 100644 drivers/staging/mgakms/matroxfb_DAC1064.c
> >>  create mode 100644 drivers/staging/mgakms/matroxfb_DAC1064.h
> >>  create mode 100644 drivers/staging/mgakms/matroxfb_Ti3026.c
> >>  create mode 100644 drivers/staging/mgakms/matroxfb_Ti3026.h
> >>  create mode 100644 drivers/staging/mgakms/matroxfb_accel.c
> >>  create mode 100644 drivers/staging/mgakms/matroxfb_accel.h
> >>  create mode 100644 drivers/staging/mgakms/matroxfb_base.c
> >>  create mode 100644 drivers/staging/mgakms/matroxfb_base.h
> >>  create mode 100644 drivers/staging/mgakms/matroxfb_crtc2.h
> >>  create mode 100644 drivers/staging/mgakms/matroxfb_g450.c
> >>  create mode 100644 drivers/staging/mgakms/matroxfb_g450.h
> >>  create mode 100644 drivers/staging/mgakms/matroxfb_maven.h
> >>  create mode 100644 drivers/staging/mgakms/matroxfb_misc.c
> >>  create mode 100644 drivers/staging/mgakms/matroxfb_misc.h
> >>  create mode 100644 drivers/staging/mgakms/mga_device.c
> >>  create mode 100644 drivers/staging/mgakms/mga_device.h
> >>  create mode 100644 drivers/staging/mgakms/mga_drv.c
> >>  create mode 100644 drivers/staging/mgakms/mga_drv.h
> >>  create mode 100644 include/drm/drm_fbconv_helper.h
> >>
> >> --
> >> 2.23.0
> >>
> >
>
> --
> Thomas Zimmermann
> Graphics Driver Developer
> SUSE Software Solutions Germany GmbH
> Maxfeldstr. 5, 90409 Nürnberg, Germany
> (HRB 36809, AG Nürnberg)
> Geschäftsführer: Felix Imendörffer
>
Greg KH Oct. 15, 2019, 6:05 p.m. UTC | #6
On Tue, Oct 15, 2019 at 07:48:29PM +0200, Daniel Vetter wrote:
> On Tue, Oct 15, 2019 at 7:28 PM Thomas Zimmermann <tzimmermann@suse.de> wrote:
> >
> > Hi Daniel
> >
> > Am 15.10.19 um 16:33 schrieb Daniel Vetter:
> > > Hi Thomas,
> > >
> > > On Mon, Oct 14, 2019 at 04:04:01PM +0200, Thomas Zimmermann wrote:
> > >> (was: DRM driver for fbdev devices)
> > >>
> > >> This is version 2 of the fbdev conversion helpers. It's more or less a
> > >> rewrite of the original patchset.
> > >>
> > >> The fbdev subsystem is considered legacy and will probably be removed at
> > >> some point. This would mean the loss of a signifanct number of drivers.
> > >> Some of the affected hardware is not in use any longer, but some hardware
> > >> is still around and provides good(-enough) framebuffers.
> > >>
> > >> The fbconv helpers allow for running the current DRM stack on top of fbdev
> > >> drivers. It's a set of functions that convert between fbdev interfaces and
> > >> DRM interfaces. Based on SHMEM and simple KMS helpers, it only offers the
> > >> basic functionality of a framebuffer, but should be compatible with most
> > >> existing fbdev drivers.
> > >>
> > >> A DRM driver using fbconv helpers consists of
> > >>
> > >>   * DRM stub code that calls into fbconv helpers, and
> > >>   * the original fbdev driver code.
> > >>
> > >> The fbdev driver code has to be modified to register itself with the
> > >> stub driver instead of the fbdev core framework. A tutorial on how to use
> > >> the helpers is part of this patchset. The resulting driver hybrid can be
> > >> refactored into a first-class DRM driver. The fbconv helpers contain a
> > >> number of comments, labeled 'DRM porting note', which explain the required
> > >> steps.
> > >>
> > >> I tested the current patchset with the following drivers: atyfb, aty128fb,
> > >> matroxfb, pm2fb, pm3fb, rivafb, s3fb, savagefb, sisfb, tdfxfb and tridentfb.
> > >> With each, I was able to successfully start with fbcon enabled, run weston and
> > >> X11. The drivers are available at [1]. For reference, the patchset includes
> > >> the Matrox stub driver.
> > >
> > > So I really don't want to rain on the parade here, since if you think this
> > > is useful when converting fbdev drivers I'll buy that, and I'm all for
> > > getting more modern drivers into drm.
> > >
> > > But I have a bunch of concerns with the approach you're proposing here:
> > >
> > > - we've tried staging for drm driver refactoring, it hurts. Separate tree
> > >   plus the quick pace in refactoring create lots of pains. And for small
> > >   drivers refacotoring before it's not buying you anything above
> > >   refactoring in your own personal tree. And for big drivers we're fairly
> > >   lenient with merging drivers that aren't fully polished yet, if there's
> > >   a team serious enough with cleaning up the mess. I think even merging
> > >   partial drivers directly under drivers/gpu (but behind CONFIG_BROKEN) is
> > >   better than staging.
> >
> > I mostly put this into staging, because it's the kind of code you'd
> > expect there.
> 
> Yeah, except we tried, it's a real pain. Conclusion by everyone
> involved is that staging doesn't work for the drm subsystem.

As the staging maintainer, I too agree with this.  No drm drivers/code
in staging please.

thanks,

greg k-h
Ville Syrjälä Oct. 15, 2019, 6:13 p.m. UTC | #7
On Tue, Oct 15, 2019 at 07:48:29PM +0200, Daniel Vetter wrote:
> On Tue, Oct 15, 2019 at 7:28 PM Thomas Zimmermann <tzimmermann@suse.de> wrote:
> >
> > Hi Daniel
> >
> > Am 15.10.19 um 16:33 schrieb Daniel Vetter:
> > > Hi Thomas,
> > >
> > > On Mon, Oct 14, 2019 at 04:04:01PM +0200, Thomas Zimmermann wrote:
> > >> (was: DRM driver for fbdev devices)
> > >>
> > >> This is version 2 of the fbdev conversion helpers. It's more or less a
> > >> rewrite of the original patchset.
> > >>
> > >> The fbdev subsystem is considered legacy and will probably be removed at
> > >> some point. This would mean the loss of a signifanct number of drivers.
> > >> Some of the affected hardware is not in use any longer, but some hardware
> > >> is still around and provides good(-enough) framebuffers.
> > >>
> > >> The fbconv helpers allow for running the current DRM stack on top of fbdev
> > >> drivers. It's a set of functions that convert between fbdev interfaces and
> > >> DRM interfaces. Based on SHMEM and simple KMS helpers, it only offers the
> > >> basic functionality of a framebuffer, but should be compatible with most
> > >> existing fbdev drivers.
> > >>
> > >> A DRM driver using fbconv helpers consists of
> > >>
> > >>   * DRM stub code that calls into fbconv helpers, and
> > >>   * the original fbdev driver code.
> > >>
> > >> The fbdev driver code has to be modified to register itself with the
> > >> stub driver instead of the fbdev core framework. A tutorial on how to use
> > >> the helpers is part of this patchset. The resulting driver hybrid can be
> > >> refactored into a first-class DRM driver. The fbconv helpers contain a
> > >> number of comments, labeled 'DRM porting note', which explain the required
> > >> steps.
> > >>
> > >> I tested the current patchset with the following drivers: atyfb, aty128fb,
> > >> matroxfb, pm2fb, pm3fb, rivafb, s3fb, savagefb, sisfb, tdfxfb and tridentfb.
> > >> With each, I was able to successfully start with fbcon enabled, run weston and
> > >> X11. The drivers are available at [1]. For reference, the patchset includes
> > >> the Matrox stub driver.
> > >
> > > So I really don't want to rain on the parade here, since if you think this
> > > is useful when converting fbdev drivers I'll buy that, and I'm all for
> > > getting more modern drivers into drm.
> > >
> > > But I have a bunch of concerns with the approach you're proposing here:
> > >
> > > - we've tried staging for drm driver refactoring, it hurts. Separate tree
> > >   plus the quick pace in refactoring create lots of pains. And for small
> > >   drivers refacotoring before it's not buying you anything above
> > >   refactoring in your own personal tree. And for big drivers we're fairly
> > >   lenient with merging drivers that aren't fully polished yet, if there's
> > >   a team serious enough with cleaning up the mess. I think even merging
> > >   partial drivers directly under drivers/gpu (but behind CONFIG_BROKEN) is
> > >   better than staging.
> >
> > I mostly put this into staging, because it's the kind of code you'd
> > expect there.
> 
> Yeah, except we tried, it's a real pain. Conclusion by everyone
> involved is that staging doesn't work for the drm subsystem.
> 
> > > - we've had conversion helpers before (for the legacy kms -> atomic
> > >   upgrade). They constantly broke, pretty much every release when someone
> > >   wanted to use them they first had to fix them up again. I think having
> > >   those helpers is good, but better to just have them in some branch
> > >   somewhere where it's clear that they might not work anymore on latest
> > >   upstream.
> > >
> > > - especially for some of these simple fbdev drivers I feel like just
> > >   typing a new driver from scratch might be simpler.
> > >
> > > A few more concerns specifically for your mga example:
> > >
> > > - We already have a mga driver. Might be better to integrate support for
> > >   older mgas into that than have a parallel driver.
> >
> > Two colleagues of mine, Takashi and Egbert, send a patch that added
> > support for desktop G200s to mgag200. [1] But it was rejected because
> > the devices are two old and not relevant any longer. If that opinion has
> > changed in the meantime, I wouldn't mind adding support for desktop GPUs
> > to the driver.
> 
> Hm that seems to have petered out inconclusive. I definitely think a
> merged mga driver is better than 2 drm atomic kms drivers for roughly
> the same hardware. I'm also assuming that at least for now no one
> plans to resurrect the 3d acceleration support for these old chips.
> But even then it's fairly easy to disable all that on the server
> chips.
> 
> > > - Your helper is based on simple display pipe, and I think for these old
> > >   mga chips (especially the dual pipe mga 450 and 550) simple display pipe
> > >   helper is more a hindering detour than actual help. From a quick read
> > >   through the code (especially all the custom ioctls) you definitely want
> > >   separate TV-out connector to expose all the tv mode properties (instead
> > >   of the custom ioctls).
> >
> > Around the G100, there's something like a change in generation. Before,
> > devices had only a single output and less than 8 MiB of RAM. This works
> > well with GEM SHMEM and simple KMS. Afterwards, devices have 8 MiB or
> > more and multiple outputs. GEM VRAM and the full set of helpers fit this
> > much better. Maybe having 2 drivers that share common code (or 3 with
> > the Server Engine chipsets) makes most sense.
> 
> Yeah if that's the case maybe a mga100 and mga200g driver fits better.
> Former based on simple display pipe.

The display hardware differences are quite minimal from 
1064SG to G200. G400 did add the second CRTC but essentially
nothing else changed from G200 display. G450/G550 changed
the PLLS around a bit just for the heck of it, and integrated 
the TMDS transmitter and TV encoder. And then they did even
more PLL madness with the different G200 server chip variants.

So IMO from display hw POV G100 vs. G200 split doesn't really
make sense.

And if you go to the effort of supporting dual head on G400+ then
the single head case on earlier platforms is just the same as the
single head "trivial" case on G400+, so totally different drivers
doesn't make sense there either. Also not all G400 cards have
the TVO/TMDS chip present in which case you can only use a
single head anyway (it's almost identical to a G200 card at
that point, assuming you drive the single output with the
primary CRTC).
Ville Syrjälä Oct. 15, 2019, 6:28 p.m. UTC | #8
On Tue, Oct 15, 2019 at 09:13:37PM +0300, Ville Syrjälä wrote:
> On Tue, Oct 15, 2019 at 07:48:29PM +0200, Daniel Vetter wrote:
> > On Tue, Oct 15, 2019 at 7:28 PM Thomas Zimmermann <tzimmermann@suse.de> wrote:
> > >
> > > Hi Daniel
> > >
> > > Am 15.10.19 um 16:33 schrieb Daniel Vetter:
> > > > Hi Thomas,
> > > >
> > > > On Mon, Oct 14, 2019 at 04:04:01PM +0200, Thomas Zimmermann wrote:
> > > >> (was: DRM driver for fbdev devices)
> > > >>
> > > >> This is version 2 of the fbdev conversion helpers. It's more or less a
> > > >> rewrite of the original patchset.
> > > >>
> > > >> The fbdev subsystem is considered legacy and will probably be removed at
> > > >> some point. This would mean the loss of a signifanct number of drivers.
> > > >> Some of the affected hardware is not in use any longer, but some hardware
> > > >> is still around and provides good(-enough) framebuffers.
> > > >>
> > > >> The fbconv helpers allow for running the current DRM stack on top of fbdev
> > > >> drivers. It's a set of functions that convert between fbdev interfaces and
> > > >> DRM interfaces. Based on SHMEM and simple KMS helpers, it only offers the
> > > >> basic functionality of a framebuffer, but should be compatible with most
> > > >> existing fbdev drivers.
> > > >>
> > > >> A DRM driver using fbconv helpers consists of
> > > >>
> > > >>   * DRM stub code that calls into fbconv helpers, and
> > > >>   * the original fbdev driver code.
> > > >>
> > > >> The fbdev driver code has to be modified to register itself with the
> > > >> stub driver instead of the fbdev core framework. A tutorial on how to use
> > > >> the helpers is part of this patchset. The resulting driver hybrid can be
> > > >> refactored into a first-class DRM driver. The fbconv helpers contain a
> > > >> number of comments, labeled 'DRM porting note', which explain the required
> > > >> steps.
> > > >>
> > > >> I tested the current patchset with the following drivers: atyfb, aty128fb,
> > > >> matroxfb, pm2fb, pm3fb, rivafb, s3fb, savagefb, sisfb, tdfxfb and tridentfb.
> > > >> With each, I was able to successfully start with fbcon enabled, run weston and
> > > >> X11. The drivers are available at [1]. For reference, the patchset includes
> > > >> the Matrox stub driver.
> > > >
> > > > So I really don't want to rain on the parade here, since if you think this
> > > > is useful when converting fbdev drivers I'll buy that, and I'm all for
> > > > getting more modern drivers into drm.
> > > >
> > > > But I have a bunch of concerns with the approach you're proposing here:
> > > >
> > > > - we've tried staging for drm driver refactoring, it hurts. Separate tree
> > > >   plus the quick pace in refactoring create lots of pains. And for small
> > > >   drivers refacotoring before it's not buying you anything above
> > > >   refactoring in your own personal tree. And for big drivers we're fairly
> > > >   lenient with merging drivers that aren't fully polished yet, if there's
> > > >   a team serious enough with cleaning up the mess. I think even merging
> > > >   partial drivers directly under drivers/gpu (but behind CONFIG_BROKEN) is
> > > >   better than staging.
> > >
> > > I mostly put this into staging, because it's the kind of code you'd
> > > expect there.
> > 
> > Yeah, except we tried, it's a real pain. Conclusion by everyone
> > involved is that staging doesn't work for the drm subsystem.
> > 
> > > > - we've had conversion helpers before (for the legacy kms -> atomic
> > > >   upgrade). They constantly broke, pretty much every release when someone
> > > >   wanted to use them they first had to fix them up again. I think having
> > > >   those helpers is good, but better to just have them in some branch
> > > >   somewhere where it's clear that they might not work anymore on latest
> > > >   upstream.
> > > >
> > > > - especially for some of these simple fbdev drivers I feel like just
> > > >   typing a new driver from scratch might be simpler.
> > > >
> > > > A few more concerns specifically for your mga example:
> > > >
> > > > - We already have a mga driver. Might be better to integrate support for
> > > >   older mgas into that than have a parallel driver.
> > >
> > > Two colleagues of mine, Takashi and Egbert, send a patch that added
> > > support for desktop G200s to mgag200. [1] But it was rejected because
> > > the devices are two old and not relevant any longer. If that opinion has
> > > changed in the meantime, I wouldn't mind adding support for desktop GPUs
> > > to the driver.
> > 
> > Hm that seems to have petered out inconclusive. I definitely think a
> > merged mga driver is better than 2 drm atomic kms drivers for roughly
> > the same hardware. I'm also assuming that at least for now no one
> > plans to resurrect the 3d acceleration support for these old chips.
> > But even then it's fairly easy to disable all that on the server
> > chips.
> > 
> > > > - Your helper is based on simple display pipe, and I think for these old
> > > >   mga chips (especially the dual pipe mga 450 and 550) simple display pipe
> > > >   helper is more a hindering detour than actual help. From a quick read
> > > >   through the code (especially all the custom ioctls) you definitely want
> > > >   separate TV-out connector to expose all the tv mode properties (instead
> > > >   of the custom ioctls).
> > >
> > > Around the G100, there's something like a change in generation. Before,
> > > devices had only a single output and less than 8 MiB of RAM. This works
> > > well with GEM SHMEM and simple KMS. Afterwards, devices have 8 MiB or
> > > more and multiple outputs. GEM VRAM and the full set of helpers fit this
> > > much better. Maybe having 2 drivers that share common code (or 3 with
> > > the Server Engine chipsets) makes most sense.
> > 
> > Yeah if that's the case maybe a mga100 and mga200g driver fits better.
> > Former based on simple display pipe.
> 
> The display hardware differences are quite minimal from 
> 1064SG to G200. G400 did add the second CRTC but essentially
> nothing else changed from G200 display. G450/G550 changed
> the PLLS around a bit just for the heck of it, and integrated 
> the TMDS transmitter and TV encoder. And then they did even
> more PLL madness with the different G200 server chip variants.
> 
> So IMO from display hw POV G100 vs. G200 split doesn't really
> make sense.

Ah, I did forget that G100 and earlier don't support the
cursor 16 color mode that G200+ have. So I guess there is a
little bit of a difference there.