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 <[email protected]> >> --- >> 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
>>
>
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Felix Imendörffer
signature.asc
Description: OpenPGP digital signature
_______________________________________________ dri-devel mailing list [email protected] https://lists.freedesktop.org/mailman/listinfo/dri-devel
