From: Emil Velikov <emil.l.velikov@gmail.com>
To: Daniel Vetter <daniel@ffwll.ch>, Inki Dae <inki.dae@samsung.com>
Cc: Pekka Paalanen <pekka.paalanen@collabora.com>,
David Airlie <airlied@linux.ie>,
Daniel Vetter <daniel.vetter@ffwll.ch>,
Intel Graphics Development <intel-gfx@lists.freedesktop.org>,
DRI Development <dri-devel@lists.freedesktop.org>,
Maxime Ripard <maxime@cerno.tech>,
Thomas Zimmermann <tzimmermann@suse.de>,
Daniel Vetter <daniel.vetter@intel.com>
Subject: Re: [PATCH 8/8] drm/modifiers: Enforce consistency between the cap an IN_FORMATS
Date: Tue, 4 May 2021 15:10:57 +0100 [thread overview]
Message-ID: <CACvgo50frye2h5L78YKnHm8TaE9xM=fn-7fNNtHbSwiv+GnYVA@mail.gmail.com> (raw)
In-Reply-To: <YIgB76WmQijHCJeV@phenom.ffwll.local>
Hi Daniel,
Thanks for the extra clarification.
On Tue, 27 Apr 2021 at 13:22, Daniel Vetter <daniel@ffwll.ch> wrote:
>
> On Tue, Apr 27, 2021 at 12:32:19PM +0100, Emil Velikov wrote:
> > Hi Daniel,
> >
> > On Tue, 27 Apr 2021 at 10:20, Daniel Vetter <daniel.vetter@ffwll.ch> wrote:
> >
> > > @@ -360,6 +373,9 @@ static int __drm_universal_plane_init(struct drm_device *dev,
> > > * drm_universal_plane_init() to let the DRM managed resource infrastructure
> > > * take care of cleanup and deallocation.
> > > *
> > > + * Drivers supporting modifiers must set @format_modifiers on all their planes,
> > > + * even those that only support DRM_FORMAT_MOD_LINEAR.
> > > + *
> > The comment says "must", yet we have an "if (format_modifiers)" in the codebase.
> > Shouldn't we add a WARN_ON() + return -EINVAL (or similar) so people
> > can see and fix their drivers?
>
> This is a must only for drivers supporting modifiers, not all drivers.
> Hence the check in the if. I did add WARN_ON for the combos that get stuff
> wrong though (like only supply one side of the modifier info, not both).
>
Hmm you're spot on - the arm/malidp patch threw me off for a minute.
> > As a follow-up one could even go a step further, by erroring out when
> > the driver hasn't provided valid modifier(s) and even removing
> > config::allow_fb_modifiers all together.
>
> Well that currently only exists to avoid walking the plane list (which we
> need to do for validation that all planes are the same). It's quite tricky
> code for tiny benefit, so I don't think it's worth it trying to remove
> allow_fb_modifiers completely.
>
Pardon if I'm saying something painfully silly - it's been a while
since I've looked closely at KMS.
From some grepping around, removing ::allow_fb_modifiers would be OK
although it's a secondary goal. It feels like the bigger win will be
simpler modifier handling in DRM.
In particular, one could always "inject" the linear modifier within
drm_universal_plane_init() and always expose DRM_CAP_ADDFB2_MODIFIERS.
Some drivers mxsfb, mgag200, stm and likely others already advertise
the CAP, even though they seemingly lack any modifiers.
The linear/invalid cargo-cult to drm_universal_plane_init() seems
strong and this series adds even more.
Another plus of always exposing the CAP, is that one could mandate (or
nuke) optional .format_mod_supported that you/Ville discussed
earlier[1].
Currently things are weird, since it's required to create IN_FORMAT
blob, yet drivers lack it while simultaneously exposing the CAP to
userspace.
One such example is exynos... Although recently it recently dropped
`allow_fb_modifiers = true` and there are no modifiers passed to
drm_universal_plane_init(), so the CAP is no longer supported.
Inki you might want to check, if that broke your userspace.
Tl:Dr: There _might_ be value in simplifying the modifier handling
_after_ these fixes land.
[1] https://lore.kernel.org/dri-devel/CAKMK7uGNP5us8KFffnPwq7g4b0-B2q-m7deqz_rPHtCrh_qUTw@mail.gmail.com/
> > Although for stable - this series + WARN_ON (no return since it might
> > break buggy drivers) sounds good.
> >
> > > @@ -909,6 +909,8 @@ struct drm_mode_config {
> > > * @allow_fb_modifiers:
> > > *
> > > * Whether the driver supports fb modifiers in the ADDFB2.1 ioctl call.
> > > + * Note that drivers should not set this directly, it is automatically
> > > + * set in drm_universal_plane_init().
> > > *
> > > * IMPORTANT:
> > > *
> > The new note and the existing IMPORTANT are in a weird mix.
> > Quoting the latter since it doesn't show in the diff.
> >
> > If this is set the driver must fill out the full implicit modifier
> > information in their &drm_mode_config_funcs.fb_create hook for legacy
> > userspace which does not set modifiers. Otherwise the GETFB2 ioctl is
> > broken for modifier aware userspace.
> >
> > In particular:
> > As the new note says "don't set it" and the existing note one says "if
> > it's set". Yet no drivers do "if (config->allow_fb_modifiers)".
> >
> > Sadly, nothing comes to mind atm wrt alternative wording.
>
> Yeah it's a bit disappointing.
>
> > With the WARN_ON() added or s/must/should/ in the documentation, the series is:
>
> With my clarification, can you please recheck whether as-is it's not
> correct?
>
Indeed - with the series as-is my RB stands.
Thanks
-Emil
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next prev parent reply other threads:[~2021-05-04 14:11 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-27 9:20 [PATCH 1/8] drm/arm: Don't set allow_fb_modifiers explicitly Daniel Vetter
2021-04-27 9:20 ` [PATCH 2/8] drm/arm/malidp: Always list modifiers Daniel Vetter
2021-04-27 15:41 ` Liviu Dudau
2021-04-27 9:20 ` [PATCH 3/8] drm/i915: Don't set allow_fb_modifiers explicitly Daniel Vetter
2021-04-27 9:20 ` [PATCH 4/8] drm/msm/dpu1: " Daniel Vetter
2021-04-27 9:20 ` [PATCH 5/8] drm/msm/mdp4: Fix modifier support enabling Daniel Vetter
2021-04-27 9:20 ` [PATCH 6/8] drm/nouveau: Don't set allow_fb_modifiers explicitly Daniel Vetter
2021-04-27 9:20 ` [PATCH 7/8] drm/stm: " Daniel Vetter
2021-04-29 19:35 ` Philippe CORNU - foss
2021-04-27 9:20 ` [PATCH 8/8] drm/modifiers: Enforce consistency between the cap an IN_FORMATS Daniel Vetter
2021-04-27 9:30 ` Simon Ser
2021-04-27 11:32 ` Emil Velikov
2021-04-27 12:22 ` Daniel Vetter
2021-05-04 14:10 ` Emil Velikov [this message]
2021-05-04 14:58 ` Simon Ser
2021-05-04 15:48 ` Emil Velikov
2021-05-04 13:38 ` Pekka Paalanen
2021-05-05 19:24 ` Daniel Vetter
2021-05-06 9:55 ` Daniel Vetter
2021-04-27 15:25 ` [PATCH 1/8] drm/arm: Don't set allow_fb_modifiers explicitly Liviu Dudau
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