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[00/30] spi: dw: Add full Baikal-T1 SPI Controllers support

Message ID 20200920112914.26501-1-Sergey.Semin@baikalelectronics.ru (mailing list archive)
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Series spi: dw: Add full Baikal-T1 SPI Controllers support | expand

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Serge Semin Sept. 20, 2020, 11:28 a.m. UTC
Originally I intended to merge a dedicated Baikal-T1 System Boot SPI
Controller driver into the kernel and leave the DW APB SSI driver
untouched. But after a long discussion (see the link at the bottom of the
letter) Mark and Andy persuaded me to integrate what we developed there
into the DW APB SSI core driver to be useful for another controllers,
which may have got the same peculiarities/problems as ours:
- No IRQ.
- No DMA.
- No GPIO CS, so a native CS is utilized.
- small Tx/Rx FIFO depth.
- Automatic CS assertion/de-assertion.
- Slow system bus.
All of them have been fixed in the framework of this patchset in some
extent at least for the SPI memory operations. As I expected it wasn't
that easy and the integration took that many patches as you can see from
the subject. Though some of them are mere cleanups or weakly related with
the subject fixes, but we just couldn't leave the code as is at some
places since we were working with the DW APB SSI driver anyway. Here is
what we did to fix the original DW APB SSI driver, to make it less messy.

First two patches are just cleanups to simplify the DW APB SSI device
initialization a bit. We suggest to discard the IRQ threshold macro as
unused and use a ternary operator to initialize the set_cs callback
instead of assigning-and-updating it.

Then we've discovered that the n_bytes field of the driver private data is
used by the DW APB SSI IRQ handler, which requires it to be initialized
before the SMP memory barrier and to be visible from another CPUs. Speaking
about the SMP memory barrier. Having one right after the shared resources
initialization is enough and there is no point in using the spin-lock to
protect the Tx/Rx buffer pointers. The protection functionality is
redundant there by the driver design. (Though I have a doubt whether the
SMP memory barrier is also required there because the normal IO-methods
like readl/writel implies a full memory barrier. So any memory operations
performed before them are supposed to be seen by devices and another CPUs.
See the patch log for details of my concern.)

Thirdly we've found out that there is some confusion in the IRQs
masking/unmasking/clearing in the SPI-transfer procedure. Multiple interrupts
are unmasked on the SPI-transfer initialization, but just TXEI is only
masked back on completion. Similarly IRQ status isn't cleared on the
controller reset, which actually makes the reset being not full and errors
prone in the controller probe procedure.

Another very important optimization is using the IO-relaxed accessors in
the dw_read_io_reg()/dw_write_io_reg() methods. Since the Tx/Rx FIFO data
registers are the most frequently accessible controller resource, using
relaxed accessors there will significantly improve the data read/write
performance. At least on Baikal-T1 SoC such modification opens up a way to
have the DW APB SSI controller working with higher SPI bus speeds, than
without it.

Fifthly we've made an effort to cleanup the code using the SPI-device
private data - chip_data. We suggest to remove the chip type from there
since it isn't used and isn't implemented right anyway. Then instead of
having a bus speed, clock divider, transfer mode preserved there, and
recalculating the CR0 fields of the SPI-device-specific phase, polarity
and frame format each time the SPI transfer is requested, we can save it
in the chip_data instance. By doing so we'll make that structure finally
used as it was supposed to by design (see the spi-fsl-dspi.c, spi-pl022.c,
spi-pxa2xx.c drivers for examples).

Sixthly instead of having the SPI-transfer specific CR0-update callback,
we suggest to implement the DW APB SSI controller capabilities approach.
By doing so we can now inject the vendor-specific peculiarities in
different parts of the DW APB SSI core driver (which is required to
implement both SPI-transfers and the SPI memory operations). This will
also make the code less confusing like defining a callback in the core
driver, setting it up in the glue layer, then calling it from the core
driver again. Seeing the small capabilities implementation embedded
in-situ is more readable than tracking the callbacks assignments. This
will concern the CS-override, Keembay master setup, DW SSI-specific CR0
registers layout capabilities.

Seventhly since there are going to be two types of the transfers
implemented in the DW APB SSI core driver, we need a common method to set
the controller configuration like, Tx/Rx-mode, bus speed, data frame size
and number of data frames to read in case of the memory operations. So we
just detached the corresponding code from the SPI-transfer-one method and
made it to be a part of the new dw_spi_update_config() function, which is
former update_cr0(). Note that the new method will be also useful for the
glue drivers, which due to the hardware design need to create their own
memory operations (for instance, for the dirmap-operations provided in the
Baikal-T System Boot SPI controller driver).

Eighthly it is the data IO procedure and IRQ-based SPI-transfer
implementation refactoring. The former one will look much simpler if the
buffers initial pointers and the buffers length data utilized instead of
the Tx/Rx buffers start and end pointers. The later one currently lacks of
valid execution at the final stage of the SPI-transfer. So if there is no
data left to send, but there is still data which needs to be received, the
Tx FIFO Empty IRQ will constantly happen until all of the requested
inbound data is received. So we suggest to fix that by taking the Rx FIFO
Empty IRQ into account.

Ninthly it's potentially errors prone to enable the DW APB SSI interrupts
before enabling the chip. It specifically concerns a case if for some
reason the DW APB SSI IRQs handler is executed before the controller is
enabled. That will cause a part of the outbound data loss. So we suggest
to reverse the order.

Tenthly in order to be able to pre-initialize the Tx FIFO with data and
only the start the SPI memory operations we need to have any CS
de-activated. We'll fulfil that requirement by explicitly clearing the CS
on the SPI transfer completion and at the explicit controller reset.

Then seeing all the currently available and potentially being created
types of the SPI transfers need to perform the DW APB SSI controller
status register check and the errors handler procedure, we've created a
common method for all of them.

Eleventhly if before we've mostly had a series of fixups, cleanups and
refactorings, here we've finally come to the new functionality
implementation. It concerns the poll-based transfer (as Baikal-T1 System
Boot SPI controller lacks a dedicated IRQ lane connected) and the SPI
memory operations implementation. If the former feature is pretty much
straightforward (see the patch log for details), the later one is a bit
tricky. It's based on the EEPROM-read (write-then-read) and the Tx-only
modes of the DW APB SSI controller, which as performing the automatic data
read and write let's us to implement the faster IO procedure than using
the Tx-Rx-mode-based approach. Having the memory-operations implemented
that way is the best thing we can currently do to provide the errors-less
SPI transfers to SPI devices with native CS attached.

Note the approach utilized here to develop the SPI memory operations can
be also used to create the "automatic CS toggle problem"-free(ish) SPI
transfers (combine SPI-message transfers into two buffers, disable
interrupts, push-pull the combined data). But we don't provide a solution
in the framework of this patchset. It is a matter of a dedicated one,
which we currently don't intend to spend our time on.

Finally at the closure of the this patchset you'll find patches, which
provide the Baikal-T1-specific DW APB SSI controllers support. The SoC has
got three SPI controllers. Two of them are pretty much normal DW APB SSI
interfaces: with IRQ, DMA, FIFOs of 64 words depth, 4x CSs. But the third
one as being a part of the Baikal-T1 System Boot Controller has got a very
limited resources: no IRQ, no DMA, only a single native chip-select and
Tx/Rx FIFOs with just 8 words depth available. In order to provide a
transparent initial boot code execution the System Boot SPI Controller is
also utilized by an vendor-specific IP-block, which exposes an SPI flash
memory direct mapping interface. Please see the corresponding patch for
details.

Link: https://lore.kernel.org/linux-spi/20200508093621.31619-1-Sergey.Semin@baikalelectronics.ru/

[1] "LINUX KERNEL MEMORY BARRIERS", Documentation/memory-barriers.txt,
    Section "KERNEL I/O BARRIER EFFECTS"

Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
Cc: Alexey Malahov <Alexey.Malahov@baikalelectronics.ru>
Cc: Ramil Zaripov <Ramil.Zaripov@baikalelectronics.ru>
Cc: Pavel Parkhomenko <Pavel.Parkhomenko@baikalelectronics.ru>
Cc: Andy Shevchenko <andy.shevchenko@gmail.com>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Lars Povlsen <lars.povlsen@microchip.com>
Cc: wuxu.wu <wuxu.wu@huawei.com>
Cc: Feng Tang <feng.tang@intel.com>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: linux-spi@vger.kernel.org
Cc: devicetree@vger.kernel.org
Cc: linux-kernel@vger.kernel.org

Serge Semin (30):
  spi: dw: Discard IRQ threshold macro
  spi: dw: Use ternary op to init set_cs callback
  spi: dw: Initialize n_bytes before the memory barrier
  Revert: spi: spi-dw: Add lock protect dw_spi rx/tx to prevent
    concurrent calls
  spi: dw: Clear IRQ status on DW SPI controller reset
  spi: dw: Disable all IRQs when controller is unused
  spi: dw: Use relaxed IO-methods to access FIFOs
  spi: dw: Discard DW SSI chip type storages
  spi: dw: Convert CS-override to DW SPI capabilities
  spi: dw: Add KeemBay Master capability
  spi: dw: Add DWC SSI capability
  spi: dw: Detach SPI device specific CR0 config method
  spi: dw: Update SPI bus speed in a config function
  spi: dw: Simplify the SPI bus speed config procedure
  spi: dw: Update Rx sample delay in the config function
  spi: dw: Add DW SPI controller config structure
  spi: dw: Refactor data IO procedure
  spi: dw: Refactor IRQ-based SPI transfer procedure
  spi: dw: Perform IRQ setup in a dedicated function
  spi: dw: Unmask IRQs after enabling the chip
  spi: dw: Discard chip enabling on DMA setup error
  spi: dw: De-assert chip-select on reset
  spi: dw: Explicitly de-assert CS on SPI transfer completion
  spi: dw: Move num-of retries parameter to the header file
  spi: dw: Add generic DW SSI status-check method
  spi: dw: Add memory operations support
  spi: dw: Introduce max mem-ops SPI bus frequency setting
  spi: dw: Add poll-based SPI transfers support
  dt-bindings: spi: dw: Add Baikal-T1 SPI Controllers
  spi: dw: Add Baikal-T1 SPI Controller glue driver

 .../bindings/spi/snps,dw-apb-ssi.yaml         |  33 +-
 drivers/spi/Kconfig                           |  29 +
 drivers/spi/Makefile                          |   1 +
 drivers/spi/spi-dw-bt1.c                      | 339 +++++++++
 drivers/spi/spi-dw-core.c                     | 642 ++++++++++++++----
 drivers/spi/spi-dw-dma.c                      |  16 +-
 drivers/spi/spi-dw-mmio.c                     |  36 +-
 drivers/spi/spi-dw.h                          |  85 ++-
 8 files changed, 960 insertions(+), 221 deletions(-)
 create mode 100644 drivers/spi/spi-dw-bt1.c

Comments

Mark Brown Sept. 29, 2020, 2:43 p.m. UTC | #1
On Sun, Sep 20, 2020 at 02:28:44PM +0300, Serge Semin wrote:

> First two patches are just cleanups to simplify the DW APB SSI device
> initialization a bit. We suggest to discard the IRQ threshold macro as
> unused and use a ternary operator to initialize the set_cs callback
> instead of assigning-and-updating it.

> Then we've discovered that the n_bytes field of the driver private data is
> used by the DW APB SSI IRQ handler, which requires it to be initialized

This is a *huge* patch series which is a bit unweildy to review
(especially given the other 10+ patch series you sent at the same time),
once you start getting over 10 patches it's time to pay attention to
series length and the fact that you're outlining a bunch of tangentially
related areas which could have been split out easily enough.  It is much
better to send smaller sets of patches at once, or if you're sending a
lot then to split them into smaller serieses.  This will tend to make
the review more approachable which will in turn tend to make things go
faster, people are much more likely to put off going through a huge
series.
Mark Brown Sept. 29, 2020, 4:23 p.m. UTC | #2
On Sun, 20 Sep 2020 14:28:44 +0300, Serge Semin wrote:
> Originally I intended to merge a dedicated Baikal-T1 System Boot SPI
> Controller driver into the kernel and leave the DW APB SSI driver
> untouched. But after a long discussion (see the link at the bottom of the
> letter) Mark and Andy persuaded me to integrate what we developed there
> into the DW APB SSI core driver to be useful for another controllers,
> which may have got the same peculiarities/problems as ours:
> - No IRQ.
> - No DMA.
> - No GPIO CS, so a native CS is utilized.
> - small Tx/Rx FIFO depth.
> - Automatic CS assertion/de-assertion.
> - Slow system bus.
> All of them have been fixed in the framework of this patchset in some
> extent at least for the SPI memory operations. As I expected it wasn't
> that easy and the integration took that many patches as you can see from
> the subject. Though some of them are mere cleanups or weakly related with
> the subject fixes, but we just couldn't leave the code as is at some
> places since we were working with the DW APB SSI driver anyway. Here is
> what we did to fix the original DW APB SSI driver, to make it less messy.
> 
> [...]

Applied to

   https://git.kernel.org/pub/scm/linux/kernel/git/broonie/spi.git for-next

Thanks!

[1/9] spi: dw: Discard IRQ threshold macro
      commit: 07918df724f2fed02327e3cbfe58a5d5568b2cc2
[2/9] spi: dw: Initialize n_bytes before the memory barrier
      commit: 8225c1c9a073c323f68833d136fcf94fbc75a275
[3/9] spi: spi-dw: Remove extraneous locking
      commit: 0b6bfad4cee4a3d5c49e01fa00284db4b676360e
[4/9] spi: dw: Clear IRQ status on DW SPI controller reset
      commit: a128f6ecd56a32e559889145003425b0c7d406e3
[5/9] spi: dw: Disable all IRQs when controller is unused
      commit: a1d5aa6f7f97b15e8fd917169239088823471741
[6/9] spi: dw: Use relaxed IO-methods to access FIFOs
      commit: 7e31cea7d1e0f4b683dc45c21530cd3ee82559b4
[7/9] spi: dw: Discard DW SSI chip type storages
      commit: 675e7c9d71cedee3988b554c47971be77e72d2db
[8/9] spi: dw: Convert CS-override to DW SPI capabilities
      commit: cc760f3143f53ea8387cd76cffc43bdc89db9df4
[9/9] spi: dw: Add KeemBay Master capability
      commit: ffb7ca54c95b4c76ad8a9aa1b2b16d61df2a7139

All being well this means that it will be integrated into the linux-next
tree (usually sometime in the next 24 hours) and sent to Linus during
the next merge window (or sooner if it is a bug fix), however if
problems are discovered then the patch may be dropped or reverted.

You may get further e-mails resulting from automated or manual testing
and review of the tree, please engage with people reporting problems and
send followup patches addressing any issues that are reported if needed.

If any updates are required or you are submitting further changes they
should be sent as incremental updates against current git, existing
patches will not be replaced.

Please add any relevant lists and maintainers to the CCs when replying
to this mail.

Thanks,
Mark
Serge Semin Sept. 29, 2020, 10:43 p.m. UTC | #3
Hi Mark

On Tue, Sep 29, 2020 at 03:43:51PM +0100, Mark Brown wrote:
> On Sun, Sep 20, 2020 at 02:28:44PM +0300, Serge Semin wrote:
> 
> > First two patches are just cleanups to simplify the DW APB SSI device
> > initialization a bit. We suggest to discard the IRQ threshold macro as
> > unused and use a ternary operator to initialize the set_cs callback
> > instead of assigning-and-updating it.
> 
> > Then we've discovered that the n_bytes field of the driver private data is
> > used by the DW APB SSI IRQ handler, which requires it to be initialized
> 

> This is a *huge* patch series which is a bit unweildy to review
> (especially given the other 10+ patch series you sent at the same time),

Yeah, sorry about the bulky series. If most of the changes have been more
complicated than that, less inter-dependent and less directed to having the code
prepared for the main alterations I would have definitely split them up in
different series. But the biggest part of the patchset is just a preparation
before adding the mem-ops, poll-based transfers and Baikal-T1 SPI support. So
having them submitted without the main part of the patchset would be just weird.

The other 10+ patches were sent months ago. I've just resent them with minor
alterations to get more attention.) Anyway since they concern an absolutely
different functionality (DW APB SSI DMA driver) of course I've delivered them in
the framework of the different patchset.

> once you start getting over 10 patches it's time to pay attention to
> series length and the fact that you're outlining a bunch of tangentially
> related areas which could have been split out easily enough.  It is much
> better to send smaller sets of patches at once, or if you're sending a
> lot then to split them into smaller serieses.  This will tend to make
> the review more approachable which will in turn tend to make things go
> faster, people are much more likely to put off going through a huge
> series.

I see you have already merged in the first nine patches. So would you like me
to split the rest of them up into two series or it would be ok to resend (if
required) them as one series seeing it's not that bulky anymore?

-Sergey
Mark Brown Sept. 30, 2020, 11:04 a.m. UTC | #4
On Wed, Sep 30, 2020 at 01:43:03AM +0300, Serge Semin wrote:
> On Tue, Sep 29, 2020 at 03:43:51PM +0100, Mark Brown wrote:

> > This is a *huge* patch series which is a bit unweildy to review
> > (especially given the other 10+ patch series you sent at the same time),

> Yeah, sorry about the bulky series. If most of the changes have been more
> complicated than that, less inter-dependent and less directed to having the code
> prepared for the main alterations I would have definitely split them up in
> different series. But the biggest part of the patchset is just a preparation
> before adding the mem-ops, poll-based transfers and Baikal-T1 SPI support. So
> having them submitted without the main part of the patchset would be just weird.

One option with things like this is to just not send everything at once
- even when split into multiple series it's a huge bulk of patches in an
inbox.  Unless the patches are obviously from their subjects repetitive
people probably aren't getting far enough in to look at the actual
patches or even their sizes before deciding it looks like a lot of work
and putting things off for later.

> I see you have already merged in the first nine patches. So would you like me
> to split the rest of them up into two series or it would be ok to resend (if
> required) them as one series seeing it's not that bulky anymore?

Not all of the first 9, IIRC I skipped one I had comments on.  If they
can be split that would probably be helpful, if there are dependencies
then it's not going to buy too much.
Serge Semin Sept. 30, 2020, 1:11 p.m. UTC | #5
On Wed, Sep 30, 2020 at 12:04:04PM +0100, Mark Brown wrote:
> On Wed, Sep 30, 2020 at 01:43:03AM +0300, Serge Semin wrote:
> > On Tue, Sep 29, 2020 at 03:43:51PM +0100, Mark Brown wrote:
> 
> > > This is a *huge* patch series which is a bit unweildy to review
> > > (especially given the other 10+ patch series you sent at the same time),
> 
> > Yeah, sorry about the bulky series. If most of the changes have been more
> > complicated than that, less inter-dependent and less directed to having the code
> > prepared for the main alterations I would have definitely split them up in
> > different series. But the biggest part of the patchset is just a preparation
> > before adding the mem-ops, poll-based transfers and Baikal-T1 SPI support. So
> > having them submitted without the main part of the patchset would be just weird.
> 
> One option with things like this is to just not send everything at once
> - even when split into multiple series it's a huge bulk of patches in an
> inbox.  Unless the patches are obviously from their subjects repetitive
> people probably aren't getting far enough in to look at the actual
> patches or even their sizes before deciding it looks like a lot of work
> and putting things off for later.
> 
> > I see you have already merged in the first nine patches. So would you like me
> > to split the rest of them up into two series or it would be ok to resend (if
> > required) them as one series seeing it's not that bulky anymore?
> 

> Not all of the first 9, IIRC I skipped one I had comments on.

Yes, you skipped one and I've already given you my response on your comment
about it: [PATCH 02/30] spi: dw: Use ternary op to init set_cs callback
So have I responded to your comment on another patch:
[PATCH 11/30] spi: dw: Add DWC SSI capability .

I will need a response from you about them to go further with this patchset.

> If they
> can be split that would probably be helpful, if there are dependencies
> then it's not going to buy too much.

Well, all later patches depend on the changes introduced in the previous ones in
one way or another. So in any case that will be an incremental series of patchsets
otherwise they most likely won't get applied cleanly on the driver source code.
For now we have got 21 patch left to review:
I) First two ones you've given your comments on and are mostly related to the
patches you have already merged in.
1. 688c17cad5c2 spi: dw: Use ternary op to init set_cs callback
2. 17d0b3abc03d spi: dw: Add DWC SSI capability

II) Refactor the DW APB SSI controller config procedure.
3. 6a436c824961 spi: dw: Detach SPI device specific CR0 config method
4. 47614d60e44c spi: dw: Update SPI bus speed in a config function
5. df64a4961801 spi: dw: Simplify the SPI bus speed config procedure
6. 1a583b130bab spi: dw: Update Rx sample delay in the config function
7. 9f205a8939a2 spi: dw: Add DW SPI controller config structure

III) Refactor IRQ-based SPI transfer procedure.
8. d4fa973a3f7c spi: dw: Refactor data IO procedure
9. d998b98e3d93 spi: dw: Refactor IRQ-based SPI transfer procedure
10. 7fc419af6e67 spi: dw: Perform IRQ setup in a dedicated function
11. d3dfd997379a spi: dw: Unmask IRQs after enabling the chip
12. 6ecf589320f3 spi: dw: Discard chip enabling on DMA setup error

IV) Final preparation before adding the memory operations.
13. 84a03fad452c spi: dw: De-assert chip-select on reset
14. dd0212eb5738 spi: dw: Explicitly de-assert CS on SPI transfer completion
15. d1eea0f556cf spi: dw: Move num-of retries parameter to the header file
16. 3e70e5a6c1d9 spi: dw: Add generic DW SSI status-check method

v) Introduce memory and poll-based operations.
17. 52d733f30464 spi: dw: Add memory operations support
18. c2f45eb3d662 spi: dw: Introduce max mem-ops SPI bus frequency setting
19. ccf08869b6bd spi: dw: Add poll-based SPI transfers support

vI) Add Baikal-T1 glue-driver
20. a536c408f7aa dt-bindings: spi: dw: Add Baikal-T1 SPI Controllers
21. 791e68755ead spi: dw: Add Baikal-T1 SPI Controller glue driver

If you want I can resend the series split up as I described above. Alternatively
I can collect I) - III) into a one patchset and IV) - VI) into another one.
So to speak I'll do in whatever scenario you prefer. Just tell me which one is
more suitable for you to review.

In anyway we need to settle the issues regarding the first two patches. Please give
me your answers on the comments I've left there in response to your comments.)

-Sergey
Mark Brown Sept. 30, 2020, 2:43 p.m. UTC | #6
On Wed, Sep 30, 2020 at 04:11:15PM +0300, Serge Semin wrote:
> On Wed, Sep 30, 2020 at 12:04:04PM +0100, Mark Brown wrote:

> > Not all of the first 9, IIRC I skipped one I had comments on.

> Yes, you skipped one and I've already given you my response on your comment
> about it: [PATCH 02/30] spi: dw: Use ternary op to init set_cs callback
> So have I responded to your comment on another patch:
> [PATCH 11/30] spi: dw: Add DWC SSI capability .

> I will need a response from you about them to go further with this patchset.

I'm not sure I saw any concrete questions with those?