diff mbox series

[v3,1/4] drm: Add drm_crtc_has_vblank()

Message ID 20200120122051.25178-2-tzimmermann@suse.de (mailing list archive)
State New, archived
Headers show
Series Use no_vblank property for drivers without VBLANK | expand

Commit Message

Thomas Zimmermann Jan. 20, 2020, 12:20 p.m. UTC
The new interface drm_crtc_has_vblank() return true if vblanking has
been initialized for a certain CRTC, or false otherwise. This function
will be useful for initializing CRTC state.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
---
 drivers/gpu/drm/drm_vblank.c | 21 +++++++++++++++++++++
 include/drm/drm_vblank.h     |  1 +
 2 files changed, 22 insertions(+)

Comments

Daniel Vetter Jan. 22, 2020, 8:31 a.m. UTC | #1
On Mon, Jan 20, 2020 at 01:20:48PM +0100, Thomas Zimmermann wrote:
> The new interface drm_crtc_has_vblank() return true if vblanking has
> been initialized for a certain CRTC, or false otherwise. This function
> will be useful for initializing CRTC state.
> 
> Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
> ---
>  drivers/gpu/drm/drm_vblank.c | 21 +++++++++++++++++++++
>  include/drm/drm_vblank.h     |  1 +
>  2 files changed, 22 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c
> index 1659b13b178c..c20102899411 100644
> --- a/drivers/gpu/drm/drm_vblank.c
> +++ b/drivers/gpu/drm/drm_vblank.c
> @@ -501,6 +501,27 @@ int drm_vblank_init(struct drm_device *dev, unsigned int num_crtcs)
>  }
>  EXPORT_SYMBOL(drm_vblank_init);
>  
> +/**
> + * drm_crtc_has_vblank - test if vblanking has been initialized for
> + *                       a CRTC
> + * @crtc: the CRTC
> + *
> + * Drivers may call this function to test if vblank support is
> + * initialized for a CRTC. For most hardware this means that vblanking
> + * can also be enabled on the CRTC.
> + *
> + * Returns:
> + * True if vblanking has been initialized for the given CRTC, false
> + * otherwise.
> + */
> +bool drm_crtc_has_vblank(const struct drm_crtc *crtc)

So making this specific to a CRTC sounds like a good idea. But it's not
the reality, drm_vblank.c assumes that either everything or nothing
supports vblanks.

The reason for dev->num_crtcs is historical baggage, it predates kms by a
few years. For kms drivers the only two valid values are either 0 or
dev->mode_config.num_crtcs. Yes that's an entire different can of worms
that's been irking me since forever (ideally drm_vblank_init would somehow
loose the num_crtcs argument for kms drivers, but some drivers call this
before they've done all the drm_crtc_init calls so it's complicated).

Hence drm_dev_has_vblank as I suggested. That would also allow you to
replace a bunch of if (dev->num_crtcs) checks in drm_vblank.c, which
should help quite a bit in code readability.

Cheers, Daniel

> +{
> +	struct drm_device *dev = crtc->dev;
> +
> +	return crtc->index < dev->num_crtcs;
> +}
> +EXPORT_SYMBOL(drm_crtc_has_vblank);
> +
>  /**
>   * drm_crtc_vblank_waitqueue - get vblank waitqueue for the CRTC
>   * @crtc: which CRTC's vblank waitqueue to retrieve
> diff --git a/include/drm/drm_vblank.h b/include/drm/drm_vblank.h
> index c16c44052b3d..531a6bc12b7e 100644
> --- a/include/drm/drm_vblank.h
> +++ b/include/drm/drm_vblank.h
> @@ -206,6 +206,7 @@ struct drm_vblank_crtc {
>  };
>  
>  int drm_vblank_init(struct drm_device *dev, unsigned int num_crtcs);
> +bool drm_crtc_has_vblank(const struct drm_crtc *crtc);
>  u64 drm_crtc_vblank_count(struct drm_crtc *crtc);
>  u64 drm_crtc_vblank_count_and_time(struct drm_crtc *crtc,
>  				   ktime_t *vblanktime);
> -- 
> 2.24.1
>
Thomas Zimmermann Jan. 22, 2020, 8:53 a.m. UTC | #2
Hi

Am 22.01.20 um 09:31 schrieb Daniel Vetter:
> On Mon, Jan 20, 2020 at 01:20:48PM +0100, Thomas Zimmermann wrote:
>> The new interface drm_crtc_has_vblank() return true if vblanking has
>> been initialized for a certain CRTC, or false otherwise. This function
>> will be useful for initializing CRTC state.
>>
>> Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
>> ---
>>  drivers/gpu/drm/drm_vblank.c | 21 +++++++++++++++++++++
>>  include/drm/drm_vblank.h     |  1 +
>>  2 files changed, 22 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c
>> index 1659b13b178c..c20102899411 100644
>> --- a/drivers/gpu/drm/drm_vblank.c
>> +++ b/drivers/gpu/drm/drm_vblank.c
>> @@ -501,6 +501,27 @@ int drm_vblank_init(struct drm_device *dev, unsigned int num_crtcs)
>>  }
>>  EXPORT_SYMBOL(drm_vblank_init);
>>  
>> +/**
>> + * drm_crtc_has_vblank - test if vblanking has been initialized for
>> + *                       a CRTC
>> + * @crtc: the CRTC
>> + *
>> + * Drivers may call this function to test if vblank support is
>> + * initialized for a CRTC. For most hardware this means that vblanking
>> + * can also be enabled on the CRTC.
>> + *
>> + * Returns:
>> + * True if vblanking has been initialized for the given CRTC, false
>> + * otherwise.
>> + */
>> +bool drm_crtc_has_vblank(const struct drm_crtc *crtc)
> 
> So making this specific to a CRTC sounds like a good idea. But it's not
> the reality, drm_vblank.c assumes that either everything or nothing
> supports vblanks.
> 
> The reason for dev->num_crtcs is historical baggage, it predates kms by a
> few years. For kms drivers the only two valid values are either 0 or
> dev->mode_config.num_crtcs. Yes that's an entire different can of worms
> that's been irking me since forever (ideally drm_vblank_init would somehow
> loose the num_crtcs argument for kms drivers, but some drivers call this
> before they've done all the drm_crtc_init calls so it's complicated).

Maybe as a first step, drm_vblank_init() could use
dev->mode_config.num_crtcs if the supplied number of CRTCs is zero.

> 
> Hence drm_dev_has_vblank as I suggested. That would also allow you to
> replace a bunch of if (dev->num_crtcs) checks in drm_vblank.c, which
> should help quite a bit in code readability.

OK, but I still don't understand why this interface is better overall.
We don't loose anything by passing in the crtc instead of the device
structure. And if there's ever a per-crtc vblank initialization, we'd
have the interface in place already. The tests with "if
(dev->num_crtcs)" could probably be removed in most places in any case.

We should also consider forking the vblank code for non-KMS drivers.
While working in this, I found the support for legacy drivers is getting
in the way at times. With such a fork, legacy drivers could continue
using struct drm_vblank_crtc, while modern drivers could maybe store
vblank state directly in struct drm_crtc.

Anyway, all this is for another patch. Unless you change your mind, I'll
replace drm_crtc_has_vblank() with drm_dev_has_vblank() for the
patchset's next iteration.

Best regards
Thomas

> 
> Cheers, Daniel
> 
>> +{
>> +	struct drm_device *dev = crtc->dev;
>> +
>> +	return crtc->index < dev->num_crtcs;
>> +}
>> +EXPORT_SYMBOL(drm_crtc_has_vblank);
>> +
>>  /**
>>   * drm_crtc_vblank_waitqueue - get vblank waitqueue for the CRTC
>>   * @crtc: which CRTC's vblank waitqueue to retrieve
>> diff --git a/include/drm/drm_vblank.h b/include/drm/drm_vblank.h
>> index c16c44052b3d..531a6bc12b7e 100644
>> --- a/include/drm/drm_vblank.h
>> +++ b/include/drm/drm_vblank.h
>> @@ -206,6 +206,7 @@ struct drm_vblank_crtc {
>>  };
>>  
>>  int drm_vblank_init(struct drm_device *dev, unsigned int num_crtcs);
>> +bool drm_crtc_has_vblank(const struct drm_crtc *crtc);
>>  u64 drm_crtc_vblank_count(struct drm_crtc *crtc);
>>  u64 drm_crtc_vblank_count_and_time(struct drm_crtc *crtc,
>>  				   ktime_t *vblanktime);
>> -- 
>> 2.24.1
>>
>
Daniel Vetter Jan. 22, 2020, 9:04 a.m. UTC | #3
On Wed, Jan 22, 2020 at 09:53:42AM +0100, Thomas Zimmermann wrote:
> Hi
> 
> Am 22.01.20 um 09:31 schrieb Daniel Vetter:
> > On Mon, Jan 20, 2020 at 01:20:48PM +0100, Thomas Zimmermann wrote:
> >> The new interface drm_crtc_has_vblank() return true if vblanking has
> >> been initialized for a certain CRTC, or false otherwise. This function
> >> will be useful for initializing CRTC state.
> >>
> >> Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
> >> ---
> >>  drivers/gpu/drm/drm_vblank.c | 21 +++++++++++++++++++++
> >>  include/drm/drm_vblank.h     |  1 +
> >>  2 files changed, 22 insertions(+)
> >>
> >> diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c
> >> index 1659b13b178c..c20102899411 100644
> >> --- a/drivers/gpu/drm/drm_vblank.c
> >> +++ b/drivers/gpu/drm/drm_vblank.c
> >> @@ -501,6 +501,27 @@ int drm_vblank_init(struct drm_device *dev, unsigned int num_crtcs)
> >>  }
> >>  EXPORT_SYMBOL(drm_vblank_init);
> >>  
> >> +/**
> >> + * drm_crtc_has_vblank - test if vblanking has been initialized for
> >> + *                       a CRTC
> >> + * @crtc: the CRTC
> >> + *
> >> + * Drivers may call this function to test if vblank support is
> >> + * initialized for a CRTC. For most hardware this means that vblanking
> >> + * can also be enabled on the CRTC.
> >> + *
> >> + * Returns:
> >> + * True if vblanking has been initialized for the given CRTC, false
> >> + * otherwise.
> >> + */
> >> +bool drm_crtc_has_vblank(const struct drm_crtc *crtc)
> > 
> > So making this specific to a CRTC sounds like a good idea. But it's not
> > the reality, drm_vblank.c assumes that either everything or nothing
> > supports vblanks.
> > 
> > The reason for dev->num_crtcs is historical baggage, it predates kms by a
> > few years. For kms drivers the only two valid values are either 0 or
> > dev->mode_config.num_crtcs. Yes that's an entire different can of worms
> > that's been irking me since forever (ideally drm_vblank_init would somehow
> > loose the num_crtcs argument for kms drivers, but some drivers call this
> > before they've done all the drm_crtc_init calls so it's complicated).
> 
> Maybe as a first step, drm_vblank_init() could use
> dev->mode_config.num_crtcs if the supplied number of CRTCs is zero.
> 
> > 
> > Hence drm_dev_has_vblank as I suggested. That would also allow you to
> > replace a bunch of if (dev->num_crtcs) checks in drm_vblank.c, which
> > should help quite a bit in code readability.
> 
> OK, but I still don't understand why this interface is better overall.
> We don't loose anything by passing in the crtc instead of the device
> structure. And if there's ever a per-crtc vblank initialization, we'd
> have the interface in place already. The tests with "if
> (dev->num_crtcs)" could probably be removed in most places in any case.

You can't use it in drm_vblank.c code, because we only have the
drm_device, not the drm_crtc (in most places at least). Your other patch
series to deprecate the drm_device callbacks for vblanks is a huge step
into the direction to fix that, but still more work needed: We'd
essentially need to copypaste drm_vblank.c into drm_crtc_vblank.c for kms
drivers, and in that copy switch from (dev, pipe) to crtc everywhere. Plus
then move the drm_vblank structure into struct drm_crtc.

Wrt removing the check: In a pile of cases it changes the return value,
which matters both for vblank usage in helper code and the ioctl itself.
From a quick look most of the checks that don't matter are already wrapped
in a WARN.

> We should also consider forking the vblank code for non-KMS drivers.
> While working in this, I found the support for legacy drivers is getting
> in the way at times. With such a fork, legacy drivers could continue
> using struct drm_vblank_crtc, while modern drivers could maybe store
> vblank state directly in struct drm_crtc.

Hm if you want to do all that then the drm_crtc_has_vblank makes sense.
But only after we've done the full split. So maybe make the public
function drm_crtc_has_vblank, which calls the internal-only
drm_has_vblank, and use that internally in drm_vblank.c?

btw I still think a sub-struct for vblank stuff in drm_crtc makes sense,
and drm_vblank_crtc seems to mostly fit the bill.

That way we're at least not adding the the conversion pain of switching
the vblank code over to drm_crtc fully.

Thoughts?
-Daniel

> Anyway, all this is for another patch. Unless you change your mind, I'll
> replace drm_crtc_has_vblank() with drm_dev_has_vblank() for the
> patchset's next iteration.
> 
> Best regards
> Thomas
> 
> > 
> > Cheers, Daniel
> > 
> >> +{
> >> +	struct drm_device *dev = crtc->dev;
> >> +
> >> +	return crtc->index < dev->num_crtcs;
> >> +}
> >> +EXPORT_SYMBOL(drm_crtc_has_vblank);
> >> +
> >>  /**
> >>   * drm_crtc_vblank_waitqueue - get vblank waitqueue for the CRTC
> >>   * @crtc: which CRTC's vblank waitqueue to retrieve
> >> diff --git a/include/drm/drm_vblank.h b/include/drm/drm_vblank.h
> >> index c16c44052b3d..531a6bc12b7e 100644
> >> --- a/include/drm/drm_vblank.h
> >> +++ b/include/drm/drm_vblank.h
> >> @@ -206,6 +206,7 @@ struct drm_vblank_crtc {
> >>  };
> >>  
> >>  int drm_vblank_init(struct drm_device *dev, unsigned int num_crtcs);
> >> +bool drm_crtc_has_vblank(const struct drm_crtc *crtc);
> >>  u64 drm_crtc_vblank_count(struct drm_crtc *crtc);
> >>  u64 drm_crtc_vblank_count_and_time(struct drm_crtc *crtc,
> >>  				   ktime_t *vblanktime);
> >> -- 
> >> 2.24.1
> >>
> > 
> 
> -- 
> Thomas Zimmermann
> Graphics Driver Developer
> SUSE Software Solutions Germany GmbH
> Maxfeldstr. 5, 90409 Nürnberg, Germany
> (HRB 36809, AG Nürnberg)
> Geschäftsführer: Felix Imendörffer
>
Thomas Zimmermann Jan. 22, 2020, 9:42 a.m. UTC | #4
Hi

Am 22.01.20 um 10:04 schrieb Daniel Vetter:
> On Wed, Jan 22, 2020 at 09:53:42AM +0100, Thomas Zimmermann wrote:
>> Hi
>>
>> Am 22.01.20 um 09:31 schrieb Daniel Vetter:
>>> On Mon, Jan 20, 2020 at 01:20:48PM +0100, Thomas Zimmermann wrote:
>>>> The new interface drm_crtc_has_vblank() return true if vblanking has
>>>> been initialized for a certain CRTC, or false otherwise. This function
>>>> will be useful for initializing CRTC state.
>>>>
>>>> Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
>>>> ---
>>>>  drivers/gpu/drm/drm_vblank.c | 21 +++++++++++++++++++++
>>>>  include/drm/drm_vblank.h     |  1 +
>>>>  2 files changed, 22 insertions(+)
>>>>
>>>> diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c
>>>> index 1659b13b178c..c20102899411 100644
>>>> --- a/drivers/gpu/drm/drm_vblank.c
>>>> +++ b/drivers/gpu/drm/drm_vblank.c
>>>> @@ -501,6 +501,27 @@ int drm_vblank_init(struct drm_device *dev, unsigned int num_crtcs)
>>>>  }
>>>>  EXPORT_SYMBOL(drm_vblank_init);
>>>>  
>>>> +/**
>>>> + * drm_crtc_has_vblank - test if vblanking has been initialized for
>>>> + *                       a CRTC
>>>> + * @crtc: the CRTC
>>>> + *
>>>> + * Drivers may call this function to test if vblank support is
>>>> + * initialized for a CRTC. For most hardware this means that vblanking
>>>> + * can also be enabled on the CRTC.
>>>> + *
>>>> + * Returns:
>>>> + * True if vblanking has been initialized for the given CRTC, false
>>>> + * otherwise.
>>>> + */
>>>> +bool drm_crtc_has_vblank(const struct drm_crtc *crtc)
>>>
>>> So making this specific to a CRTC sounds like a good idea. But it's not
>>> the reality, drm_vblank.c assumes that either everything or nothing
>>> supports vblanks.
>>>
>>> The reason for dev->num_crtcs is historical baggage, it predates kms by a
>>> few years. For kms drivers the only two valid values are either 0 or
>>> dev->mode_config.num_crtcs. Yes that's an entire different can of worms
>>> that's been irking me since forever (ideally drm_vblank_init would somehow
>>> loose the num_crtcs argument for kms drivers, but some drivers call this
>>> before they've done all the drm_crtc_init calls so it's complicated).
>>
>> Maybe as a first step, drm_vblank_init() could use
>> dev->mode_config.num_crtcs if the supplied number of CRTCs is zero.
>>
>>>
>>> Hence drm_dev_has_vblank as I suggested. That would also allow you to
>>> replace a bunch of if (dev->num_crtcs) checks in drm_vblank.c, which
>>> should help quite a bit in code readability.
>>
>> OK, but I still don't understand why this interface is better overall.
>> We don't loose anything by passing in the crtc instead of the device
>> structure. And if there's ever a per-crtc vblank initialization, we'd
>> have the interface in place already. The tests with "if
>> (dev->num_crtcs)" could probably be removed in most places in any case.
> 
> You can't use it in drm_vblank.c code, because we only have the
> drm_device, not the drm_crtc (in most places at least). Your other patch
> series to deprecate the drm_device callbacks for vblanks is a huge step
> into the direction to fix that, but still more work needed: We'd
> essentially need to copypaste drm_vblank.c into drm_crtc_vblank.c for kms
> drivers, and in that copy switch from (dev, pipe) to crtc everywhere. Plus
> then move the drm_vblank structure into struct drm_crtc.
> 
> Wrt removing the check: In a pile of cases it changes the return value,
> which matters both for vblank usage in helper code and the ioctl itself.
> From a quick look most of the checks that don't matter are already wrapped
> in a WARN.
> 
>> We should also consider forking the vblank code for non-KMS drivers.
>> While working in this, I found the support for legacy drivers is getting
>> in the way at times. With such a fork, legacy drivers could continue
>> using struct drm_vblank_crtc, while modern drivers could maybe store
>> vblank state directly in struct drm_crtc.
> 
> Hm if you want to do all that then the drm_crtc_has_vblank makes sense.
> But only after we've done the full split. So maybe make the public
> function drm_crtc_has_vblank, which calls the internal-only
> drm_has_vblank, and use that internally in drm_vblank.c?
> 
> btw I still think a sub-struct for vblank stuff in drm_crtc makes sense,
> and drm_vblank_crtc seems to mostly fit the bill.
> 
> That way we're at least not adding the the conversion pain of switching
> the vblank code over to drm_crtc fully.
> 
> Thoughts?

That all sounds good. Using struct drm_vblank_crtc with legacy and
modern vblank functions, might allow us to continue to share some of the
implementation.

Wrt the current interface, drm_dev_has_vblank() is only called in a
single place, so switching to drm_crtc_has_vblank() later would not be hard.

Best regards
Thomas

> -Daniel
> 
>> Anyway, all this is for another patch. Unless you change your mind, I'll
>> replace drm_crtc_has_vblank() with drm_dev_has_vblank() for the
>> patchset's next iteration.
>>
>> Best regards
>> Thomas
>>
>>>
>>> Cheers, Daniel
>>>
>>>> +{
>>>> +	struct drm_device *dev = crtc->dev;
>>>> +
>>>> +	return crtc->index < dev->num_crtcs;
>>>> +}
>>>> +EXPORT_SYMBOL(drm_crtc_has_vblank);
>>>> +
>>>>  /**
>>>>   * drm_crtc_vblank_waitqueue - get vblank waitqueue for the CRTC
>>>>   * @crtc: which CRTC's vblank waitqueue to retrieve
>>>> diff --git a/include/drm/drm_vblank.h b/include/drm/drm_vblank.h
>>>> index c16c44052b3d..531a6bc12b7e 100644
>>>> --- a/include/drm/drm_vblank.h
>>>> +++ b/include/drm/drm_vblank.h
>>>> @@ -206,6 +206,7 @@ struct drm_vblank_crtc {
>>>>  };
>>>>  
>>>>  int drm_vblank_init(struct drm_device *dev, unsigned int num_crtcs);
>>>> +bool drm_crtc_has_vblank(const struct drm_crtc *crtc);
>>>>  u64 drm_crtc_vblank_count(struct drm_crtc *crtc);
>>>>  u64 drm_crtc_vblank_count_and_time(struct drm_crtc *crtc,
>>>>  				   ktime_t *vblanktime);
>>>> -- 
>>>> 2.24.1
>>>>
>>>
>>
>> -- 
>> Thomas Zimmermann
>> Graphics Driver Developer
>> SUSE Software Solutions Germany GmbH
>> Maxfeldstr. 5, 90409 Nürnberg, Germany
>> (HRB 36809, AG Nürnberg)
>> Geschäftsführer: Felix Imendörffer
>>
> 
> 
> 
>
diff mbox series

Patch

diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c
index 1659b13b178c..c20102899411 100644
--- a/drivers/gpu/drm/drm_vblank.c
+++ b/drivers/gpu/drm/drm_vblank.c
@@ -501,6 +501,27 @@  int drm_vblank_init(struct drm_device *dev, unsigned int num_crtcs)
 }
 EXPORT_SYMBOL(drm_vblank_init);
 
+/**
+ * drm_crtc_has_vblank - test if vblanking has been initialized for
+ *                       a CRTC
+ * @crtc: the CRTC
+ *
+ * Drivers may call this function to test if vblank support is
+ * initialized for a CRTC. For most hardware this means that vblanking
+ * can also be enabled on the CRTC.
+ *
+ * Returns:
+ * True if vblanking has been initialized for the given CRTC, false
+ * otherwise.
+ */
+bool drm_crtc_has_vblank(const struct drm_crtc *crtc)
+{
+	struct drm_device *dev = crtc->dev;
+
+	return crtc->index < dev->num_crtcs;
+}
+EXPORT_SYMBOL(drm_crtc_has_vblank);
+
 /**
  * drm_crtc_vblank_waitqueue - get vblank waitqueue for the CRTC
  * @crtc: which CRTC's vblank waitqueue to retrieve
diff --git a/include/drm/drm_vblank.h b/include/drm/drm_vblank.h
index c16c44052b3d..531a6bc12b7e 100644
--- a/include/drm/drm_vblank.h
+++ b/include/drm/drm_vblank.h
@@ -206,6 +206,7 @@  struct drm_vblank_crtc {
 };
 
 int drm_vblank_init(struct drm_device *dev, unsigned int num_crtcs);
+bool drm_crtc_has_vblank(const struct drm_crtc *crtc);
 u64 drm_crtc_vblank_count(struct drm_crtc *crtc);
 u64 drm_crtc_vblank_count_and_time(struct drm_crtc *crtc,
 				   ktime_t *vblanktime);