[Nouveau] [PATCH v2] drm/nouveau: Accept 'legacy' format modifiers

[Ben Skeggs]

On Wed, 29 Jul 2020 at 12:48, Dave Airlie <airlied at gmail.com> wrote:
>
> On Tue, 28 Jul 2020 at 04:51, James Jones <jajones at nvidia.com> wrote:
> >
> > On 7/23/20 9:06 PM, Ben Skeggs wrote:
> > > On Sat, 18 Jul 2020 at 13:34, James Jones <jajones at nvidia.com> wrote:
> > >>
> > >> Accept the DRM_FORMAT_MOD_NVIDIA_16BX2_BLOCK()
> > >> family of modifiers to handle broken userspace
> > >> Xorg modesetting and Mesa drivers. Existing Mesa
> > >> drivers are still aware of only these older
> > >> format modifiers which do not differentiate
> > >> between different variations of the block linear
> > >> layout. When the format modifier support flag was
> > >> flipped in the nouveau kernel driver, the X.org
> > >> modesetting driver began attempting to use its
> > >> format modifier-enabled framebuffer path. Because
> > >> the set of format modifiers advertised by the
> > >> kernel prior to this change do not intersect with
> > >> the set of format modifiers advertised by Mesa,
> > >> allocating GBM buffers using format modifiers
> > >> fails and the modesetting driver falls back to
> > >> non-modifier allocation. However, it still later
> > >> queries the modifier of the GBM buffer when
> > >> creating its DRM-KMS framebuffer object, receives
> > >> the old-format modifier from Mesa, and attempts
> > >> to create a framebuffer with it. Since the kernel
> > >> is still not aware of these formats, this fails.
> > >>
> > >> Userspace should not be attempting to query format
> > >> modifiers of GBM buffers allocated with a non-
> > >> format-modifier-aware allocation path, but to
> > >> avoid breaking existing userspace behavior, this
> > >> change accepts the old-style format modifiers when
> > >> creating framebuffers and applying them to planes
> > >> by translating them to the equivalent new-style
> > >> modifier. To accomplish this, some layout
> > >> parameters must be assumed to match properties of
> > >> the device targeted by the relevant ioctls. To
> > >> avoid perpetuating misuse of the old-style
> > >> modifiers, this change does not advertise support
> > >> for them. Doing so would imply compatibility
> > >> between devices with incompatible memory layouts.
> > >>
> > >> Tested with Xorg 1.20 modesetting driver,
> > >> weston at c46c70dac84a4b3030cd05b380f9f410536690fc,
> > >> gnome & KDE wayland desktops from Ubuntu 18.04,
> > >> and sway 1.5
> > >>
> > >> Reported-by: Kirill A. Shutemov <kirill at shutemov.name>
> > >> Fixes: fa4f4c213f5f ("drm/nouveau/kms: Support NVIDIA format modifiers")
> > >> Link: https://lkml.org/lkml/2020/6/30/1251
> > >> Signed-off-by: James Jones <jajones at nvidia.com>
> > >> ---
> > >>   drivers/gpu/drm/nouveau/nouveau_display.c | 26 +++++++++++++++++++++--
> > >>   1 file changed, 24 insertions(+), 2 deletions(-)
> > >>
> > >> diff --git a/drivers/gpu/drm/nouveau/nouveau_display.c b/drivers/gpu/drm/nouveau/nouveau_display.c
> > >> index 496c4621cc78..31543086254b 100644
> > >> --- a/drivers/gpu/drm/nouveau/nouveau_display.c
> > >> +++ b/drivers/gpu/drm/nouveau/nouveau_display.c
> > >> @@ -191,8 +191,14 @@ nouveau_decode_mod(struct nouveau_drm *drm,
> > >>                     uint32_t *tile_mode,
> > >>                     uint8_t *kind)
> > >>   {
> > >> +       struct nouveau_display *disp = nouveau_display(drm->dev);
> > >>          BUG_ON(!tile_mode || !kind);
> > >>
> > >> +       if ((modifier & (0xffull << 12)) == 0ull) {
> > >> +               /* Legacy modifier.  Translate to this device's 'kind.' */
> > >> +               modifier |= disp->format_modifiers[0] & (0xffull << 12);
> > >> +       }
> > > I believe this should be moved into the != MOD_LINEAR case.
> >
> > Yes, of course, thanks.  I need to re-evaluate my testing yet again to
> > make sure I hit that case too.  Preparing a v3...
>
> Going to need something here in the next day, two max.
>
> Linus may wait for another week, but it's not guaranteed.
I tested a whole bunch of GPUs before sending nouveau's -next tree,
and with the change I suggested to this patch + the other stuff I sent
through -fixes already, things seemed to be in OK shape.

Ben.
>
> Dave.