linux-kernel - Re: [PATCH 05/10] drm/sun4i: Explicitly list and check formats supported by the frontend

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Message-ID: <20180329090321.3s3xaizybekqsbq5@flea>
Date:   Thu, 29 Mar 2018 11:03:21 +0200
From:   Maxime Ripard <maxime.ripard@...tlin.com>
To:     Paul Kocialkowski <paul.kocialkowski@...tlin.com>
Cc:     linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linux-arm-kernel@...ts.infradead.org,
        David Airlie <airlied@...ux.ie>, Chen-Yu Tsai <wens@...e.org>,
        Daniel Vetter <daniel.vetter@...el.com>,
        Gustavo Padovan <gustavo@...ovan.org>,
        Sean Paul <seanpaul@...omium.org>
Subject: Re: [PATCH 05/10] drm/sun4i: Explicitly list and check formats
 supported by the frontend

On Tue, Mar 27, 2018 at 10:24:17AM +0200, Paul Kocialkowski wrote:
> Hi,
> 
> On Fri, 2018-03-23 at 11:06 +0100, Maxime Ripard wrote:
> > On Wed, Mar 21, 2018 at 04:28:59PM +0100, Paul Kocialkowski wrote:
> > > In order to check whether the frontend supports a specific format,
> > > an
> > > explicit list and a related helper are introduced.
> > > 
> > > They are then used to determine whether the frontend can actually
> > > support
> > > the requested format when it was selected to be used.
> > > 
> > > Signed-off-by: Paul Kocialkowski <paul.kocialkowski@...tlin.com>
> > > ---
> > >  drivers/gpu/drm/sun4i/sun4i_backend.c  |  5 ++++
> > >  drivers/gpu/drm/sun4i/sun4i_frontend.c | 44
> > > ++++++++++++++++++++++++++++++++++
> > >  drivers/gpu/drm/sun4i/sun4i_frontend.h |  1 +
> > >  3 files changed, 50 insertions(+)
> > > 
> > > diff --git a/drivers/gpu/drm/sun4i/sun4i_backend.c
> > > b/drivers/gpu/drm/sun4i/sun4i_backend.c
> > > index 7703ba989743..1fad0714c70e 100644
> > > --- a/drivers/gpu/drm/sun4i/sun4i_backend.c
> > > +++ b/drivers/gpu/drm/sun4i/sun4i_backend.c
> > > @@ -532,6 +532,11 @@ static int sun4i_backend_atomic_check(struct
> > > sunxi_engine *engine,
> > >  		struct drm_format_name_buf format_name;
> > >  
> > >  		if (sun4i_backend_plane_uses_frontend(plane_state))
> > > {
> > > +			if (!sun4i_frontend_format_is_supported(fb-
> > > >format->format)) {
> > > +				DRM_DEBUG_DRIVER("Frontend plane
> > > check failed\n");
> > > +				return -EINVAL;
> > > +			}
> > > +
> > 
> > So you're checking if the frontend doesn't support it and if the
> > backend doesn't support it. Who supports it then? :)
> 
> That's the case case where the format is not supported by either of the
> hardware blocks. For instance, requesting ARGB with tiling will fail,
> although ARGB without tiling will work. It seems that modetest assumes
> that modifiers only apply to YUV (in which case there are no unsupported
> cases), but I think userspace might still request RGB+tiling
> combinations. I don't currently see a way to report to which format the
> tiling applies (thus we have to expect that it can come with any of the
> supported formats).

Then I guess this is a check that could be moved out of that
condition, or even as part of the generic side of atomic_check. That
looks not really specific to the driver itself.

> > Like I was saying, this should be moved to the previous patch, within
> > sun4i_backend_plane_uses_frontend.
> 
> If we get both tests (no backend support and frontend support) into one
> function, we cannot detect that the format is actually unsupported and
> return an error in the atomic check.

This is already covered by drm_atomic_plane_check:
https://elixir.bootlin.com/linux/v4.16-rc7/source/drivers/gpu/drm/drm_atomic.c#L884

So we'll only end up being called here if we have a format we support.

> > > +static const uint32_t sun4i_frontend_formats[] = {
> > > +	/* RGB */
> > > +	DRM_FORMAT_XRGB8888,
> > > +	DRM_FORMAT_BGRX8888,
> > > +	/* YUV444 */
> > > +	DRM_FORMAT_YUV444,
> > > +	DRM_FORMAT_YVU444,
> > > +	/* YUV422 */
> > > +	DRM_FORMAT_YUYV,
> > > +	DRM_FORMAT_YVYU,
> > > +	DRM_FORMAT_UYVY,
> > > +	DRM_FORMAT_VYUY,
> > > +	DRM_FORMAT_NV16,
> > > +	DRM_FORMAT_NV61,
> > > +	DRM_FORMAT_YUV422,
> > > +	DRM_FORMAT_YVU422,
> > > +	/* YUV420 */
> > > +	DRM_FORMAT_NV12,
> > > +	DRM_FORMAT_NV21,
> > > +	DRM_FORMAT_YUV420,
> > > +	DRM_FORMAT_YVU420,
> > > +	/* YUV411 */
> > > +	DRM_FORMAT_YUV411,
> > > +	DRM_FORMAT_YVU411,
> > > +};
> > 
> > I think this list should reflect what the driver currently supports,
> > not what the hardware supports.
> 
> This list is not indended to reflect what the driver supports, but only
> what the backend can support (to correctly select whether a
> format/modifier couple should go to the frontend or backend)!

I know, and it's not my point. The whole point is that you don't need
that full list in the first place to achieve what you want to achieve
with this patch.

Maxime

-- 
Maxime Ripard, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering
https://bootlin.com

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