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

[James Jones <jajones@nvidia.com>]

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...

Thanks,
-James

>> +
>>          if (modifier == DRM_FORMAT_MOD_LINEAR) {
>>                  /* tile_mode will not be used in this case */
>>                  *tile_mode = 0;
>> @@ -227,6 +233,16 @@ nouveau_framebuffer_get_layout(struct drm_framebuffer *fb,
>>          }
>>   }
>>
>> +static const u64 legacy_modifiers[] = {
>> +       DRM_FORMAT_MOD_NVIDIA_16BX2_BLOCK(0),
>> +       DRM_FORMAT_MOD_NVIDIA_16BX2_BLOCK(1),
>> +       DRM_FORMAT_MOD_NVIDIA_16BX2_BLOCK(2),
>> +       DRM_FORMAT_MOD_NVIDIA_16BX2_BLOCK(3),
>> +       DRM_FORMAT_MOD_NVIDIA_16BX2_BLOCK(4),
>> +       DRM_FORMAT_MOD_NVIDIA_16BX2_BLOCK(5),
>> +       DRM_FORMAT_MOD_INVALID
>> +};
>> +
>>   static int
>>   nouveau_validate_decode_mod(struct nouveau_drm *drm,
>>                              uint64_t modifier,
>> @@ -247,8 +263,14 @@ nouveau_validate_decode_mod(struct nouveau_drm *drm,
>>               (disp->format_modifiers[mod] != modifier);
>>               mod++);
>>
>> -       if (disp->format_modifiers[mod] == DRM_FORMAT_MOD_INVALID)
>> -               return -EINVAL;
>> +       if (disp->format_modifiers[mod] == DRM_FORMAT_MOD_INVALID) {
>> +               for (mod = 0;
>> +                    (legacy_modifiers[mod] != DRM_FORMAT_MOD_INVALID) &&
>> +                    (legacy_modifiers[mod] != modifier);
>> +                    mod++);
>> +               if (legacy_modifiers[mod] == DRM_FORMAT_MOD_INVALID)
>> +                       return -EINVAL;
>> +       }
>>
>>          nouveau_decode_mod(drm, modifier, tile_mode, kind);
>>
>> --
>> 2.17.1
>>
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