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

[Dave Airlie <airlied@gmail.com>]

On Tue, 28 Jul 2020 at 04:51, James Jones <jajones@nvidia.com> wrote:
>
> On 7/23/20 9:06 PM, Ben Skeggs wrote:
> > On Sat, 18 Jul 2020 at 13:34, James Jones <jajones@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@c46c70dac84a4b3030cd05b380f9f410536690fc,
> >> gnome & KDE wayland desktops from Ubuntu 18.04,
> >> and sway 1.5
> >>
> >> Reported-by: Kirill A. Shutemov <kirill@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@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.

Dave.
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