Re: [PATCH v2 04/10] drm/simpledrm: Compute framebuffer stride if not set

[Daniel Vetter <daniel@ffwll.ch>]

On Wed, 27 Jul 2022 at 09:53, Thomas Zimmermann <tzimmermann@suse.de> wrote:
>
> Hi
>
> Am 25.07.22 um 17:13 schrieb Javier Martinez Canillas:
> > Hello Geert,
> >
> > On 7/21/22 16:46, Geert Uytterhoeven wrote:
> >> Hi Thomas,
> >>
> >> On Wed, Jul 20, 2022 at 4:27 PM Thomas Zimmermann <tzimmermann@suse.de> wrote:
> >>> Compute the framebuffer's scanline stride length if not given by
> >>> the simplefb data.
> >>>
> >>> Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
> >>
> >> Thanks for your patch!
> >>
> >>> --- a/drivers/gpu/drm/tiny/simpledrm.c
> >>> +++ b/drivers/gpu/drm/tiny/simpledrm.c
> >>> @@ -743,6 +743,9 @@ static struct simpledrm_device *simpledrm_device_create(struct drm_driver *drv,
> >>>                  drm_err(dev, "no simplefb configuration found\n");
> >>>                  return ERR_PTR(-ENODEV);
> >>>          }
> >>> +       if (!stride)
> >>> +               stride = format->cpp[0] * width;
> >>
> >> DIV_ROUND_UP(drm_format_info_bpp(format) * width, 8)
> >>
> >
> > I think you meant here:
> >
> > DIV_ROUND_UP(drm_format_info_bpp(format, 0) * width, 8) ?
>
> I guess, that's the right function. My original code is correct, but cpp
> is also deprecated.

You all mean drm_format_info_min_pitch().

I really don't want drivers to go grab any of the legacy format info
fields like bpp or depth. switch() statements on the fourcc code for
programming registers, or one of the real helper functions in
drm_fourcc.c (there might be some gaps), but not ever going through
legacy concepts. Anything else just leads to subtle bugs when new
formats get added and oops suddenly the assumptions don't hold.

Those should be strictly limited to legacy (i.e. not drm_fourcc aware)
interfaces. Heck I think even fbdev emulation should completely switch
over to drm_fourcc/drm_format_info, but alas that's a pile of work and
not much payoff.

I'm trying to volunteer Same to add a legacy_bpp tag to the above
helper and appropriately limit it, I think limiting to formats with
depth!=0 is probably the right thing. And then we should probably
remove a pile of the cargo-culted depth!=0 entries too.
-Daniel

>
> Best regards
> Thomas
>
> >
> > With that change,
> >
> > Acked-by: Javier Martinez Canillas <javierm@redhat.com>
> >
>
> --
> Thomas Zimmermann
> Graphics Driver Developer
> SUSE Software Solutions Germany GmbH
> Maxfeldstr. 5, 90409 Nürnberg, Germany
> (HRB 36809, AG Nürnberg)
> Geschäftsführer: Ivo Totev



-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch