Re: [PATCH] drm/doc: document that PRIME import/export is always supported

[Thomas Zimmermann <tzimmermann@suse.de>]

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Hi

Am 12.07.23 um 20:32 schrieb Simon Ser:
> Since commit 6b85aa68d9d5 ("drm: Enable PRIME import/export for all
> drivers"), import/export is always supported. Document this so that
> user-space knows what to expect.
> 
> Signed-off-by: Simon Ser <contact@emersion.fr>
> Cc: Thomas Zimmermann <tzimmermann@suse.de>
> Cc: Alex Deucher <alexander.deucher@amd.com>
> Cc: Jeffrey Hugo <quic_jhugo@quicinc.com>
> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> ---
>   include/uapi/drm/drm.h | 7 +++++++
>   1 file changed, 7 insertions(+)
> 
> diff --git a/include/uapi/drm/drm.h b/include/uapi/drm/drm.h
> index a87bbbbca2d4..56c194df527e 100644
> --- a/include/uapi/drm/drm.h
> +++ b/include/uapi/drm/drm.h
> @@ -673,6 +673,9 @@ struct drm_gem_open {
>    * Bitfield of supported PRIME sharing capabilities. See &DRM_PRIME_CAP_IMPORT
>    * and &DRM_PRIME_CAP_EXPORT.
>    *
> + * Starting from kernel version 6.6, both &DRM_PRIME_CAP_IMPORT and
> + * &DRM_PRIME_CAP_EXPORT are always advertised.
> + *

When people port these changes into their trees the version becomes 
meaningless. There are so many "enterprise kernels" that combine whole 
subsystems from different upstream releases.

That makes me wonder if such documentation makes sense. We want to avoid 
a situation where userspace does

if (v6.6)
   do()
else if (test_flags())
   do()

Best regards
Thomas

>    * PRIME buffers are exposed as dma-buf file descriptors. See
>    * Documentation/gpu/drm-mm.rst, section "PRIME Buffer Sharing".
>    */
> @@ -682,6 +685,8 @@ struct drm_gem_open {
>    *
>    * If this bit is set in &DRM_CAP_PRIME, the driver supports importing PRIME
>    * buffers via the &DRM_IOCTL_PRIME_FD_TO_HANDLE ioctl.
> + *
> + * Starting from kernel version 6.6, this bit is always set in &DRM_CAP_PRIME.
>    */
>   #define  DRM_PRIME_CAP_IMPORT		0x1
>   /**
> @@ -689,6 +694,8 @@ struct drm_gem_open {
>    *
>    * If this bit is set in &DRM_CAP_PRIME, the driver supports exporting PRIME
>    * buffers via the &DRM_IOCTL_PRIME_HANDLE_TO_FD ioctl.
> + *
> + * Starting from kernel version 6.6, this bit is always set in &DRM_CAP_PRIME.
>    */
>   #define  DRM_PRIME_CAP_EXPORT		0x2
>   /**

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)

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