linux-kernel - Re: [PATCH] drm: add DRM_PRIME_CAP

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Date:   Tue, 16 Apr 2019 09:19:35 +0200
From:   Daniel Vetter <daniel@...ll.ch>
To:     Gerd Hoffmann <kraxel@...hat.com>
Cc:     dri-devel@...ts.freedesktop.org, Dave Airlie <airlied@...hat.com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <maxime.ripard@...tlin.com>,
        Sean Paul <sean@...rly.run>, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drm: add DRM_PRIME_CAP_LOCAL

On Wed, Apr 10, 2019 at 09:47:12AM +0200, Gerd Hoffmann wrote:
> Some drivers (for example qxl) support neither import nor export of
> dma-bufs.  But you can still use dma-bufs to pass buffer references
> from one process to another; drm_gem_prime_import() will figure the
> dma-buf came from the same driver and just takes a reference in that
> case instead of doing a full export/import.
> 
> Right now there is no way for userspace to figure it can do this.  Add
> the new prime capability DRM_PRIME_CAP_LOCAL to indicate that.  Set the
> bit for every driver which has the DRIVER_PRIME feature bit set.

It can just try? Any driver that supports dma-buf (even if only for
self-import) should set DRIVER_PRIME. It's perfectly fine to reject any
other sharing.
-Daniel

> 
> Cc: Dave Airlie <airlied@...hat.com>
> Signed-off-by: Gerd Hoffmann <kraxel@...hat.com>
> ---
>  include/uapi/drm/drm.h      | 1 +
>  drivers/gpu/drm/drm_ioctl.c | 2 ++
>  2 files changed, 3 insertions(+)
> 
> diff --git a/include/uapi/drm/drm.h b/include/uapi/drm/drm.h
> index 236b01a1fabf..b6157d48dc1a 100644
> --- a/include/uapi/drm/drm.h
> +++ b/include/uapi/drm/drm.h
> @@ -632,6 +632,7 @@ struct drm_gem_open {
>  #define DRM_CAP_PRIME			0x5
>  #define  DRM_PRIME_CAP_IMPORT		0x1
>  #define  DRM_PRIME_CAP_EXPORT		0x2
> +#define  DRM_PRIME_CAP_LOCAL		0x4
>  #define DRM_CAP_TIMESTAMP_MONOTONIC	0x6
>  #define DRM_CAP_ASYNC_PAGE_FLIP		0x7
>  /*
> diff --git a/drivers/gpu/drm/drm_ioctl.c b/drivers/gpu/drm/drm_ioctl.c
> index d337f161909c..00599758783b 100644
> --- a/drivers/gpu/drm/drm_ioctl.c
> +++ b/drivers/gpu/drm/drm_ioctl.c
> @@ -241,6 +241,8 @@ static int drm_getcap(struct drm_device *dev, void *data, struct drm_file *file_
>  	case DRM_CAP_PRIME:
>  		req->value |= dev->driver->prime_fd_to_handle ? DRM_PRIME_CAP_IMPORT : 0;
>  		req->value |= dev->driver->prime_handle_to_fd ? DRM_PRIME_CAP_EXPORT : 0;
> +		req->value |= (dev->driver->driver_features & DRIVER_PRIME)
> +			? DRM_PRIME_CAP_LOCAL : 0;
>  		return 0;
>  	case DRM_CAP_SYNCOBJ:
>  		req->value = drm_core_check_feature(dev, DRIVER_SYNCOBJ);
> -- 
> 2.18.1
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch