On 2024-12-16 22:29, Marek Olšák wrote: > On Mon, Dec 16, 2024 at 4:27 AM Michel Dänzer <michel.daenzer@xxxxxxxxxxx <mailto:michel.daenzer@xxxxxxxxxxx>> wrote: > > On 2024-12-15 21:53, Marek Olšák wrote: > > The comment explains the problem with DRM_FORMAT_MOD_LINEAR. > > > > Signed-off-by: Marek Olšák <marek.olsak@xxxxxxx <mailto:marek.olsak@xxxxxxx> <mailto:marek.olsak@xxxxxxx <mailto:marek.olsak@xxxxxxx>>> > > > > diff --git a/include/uapi/drm/drm_fourcc.h b/include/uapi/drm/drm_fourcc.h > > index 78abd819fd62e..8ec4163429014 100644 > > --- a/include/uapi/drm/drm_fourcc.h > > +++ b/include/uapi/drm/drm_fourcc.h > > @@ -484,9 +484,27 @@ extern "C" { > > * modifier (e.g. not setting DRM_MODE_FB_MODIFIERS in the DRM_ADDFB2 ioctl), > > * which tells the driver to also take driver-internal information into account > > * and so might actually result in a tiled framebuffer. > > + * > > + * WARNING: > > + * There are drivers out there that expose DRM_FORMAT_MOD_LINEAR, but only > > + * support a certain pitch alignment and can't import images with this modifier > > + * if the pitch alignment isn't exactly the one supported. They can however > > + * allocate images with this modifier and other drivers can import them only > > + * if they support the same pitch alignment. Thus, DRM_FORMAT_MOD_LINEAR is > > + * fundamentically incompatible across devices and is the only modifier that > > + * has a chance of not working. The PITCH_ALIGN modifiers should be used > > + * instead. > > */ > > #define DRM_FORMAT_MOD_LINEAR fourcc_mod_code(NONE, 0) > > > > +/* Linear layout modifiers with an explicit pitch alignment in bytes. > > + * Exposing this modifier requires that the pitch alignment is exactly > > + * the number in the definition. > > + */ > > +#define DRM_FORMAT_MOD_LINEAR_PITCH_ALIGN_64B fourcc_mod_code(NONE, 1) > > It's not clear what you mean by "requires that the pitch alignment is exactly the number in the definition", since a pitch which is aligned to 256 bytes is also aligned to 128 & 64 bytes. Do you mean the pitch must be exactly the width rounded up to the next / smallest possible multiple of the specified number of bytes? > > > The pitch must be width*Bpp aligned to the number of bytes in the definition. The comment above the modifier define should spell that out unambiguously. -- Earthling Michel Dänzer \ GNOME / Xwayland / Mesa developer https://redhat.com \ Libre software enthusiast
