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References: <20231027194537.408922-1-robdclark@gmail.com>
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From:   Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Date:   Sat, 28 Oct 2023 04:16:40 +0300
Message-ID: <CAA8EJpoOHqzQBESqjxCh4DHztJrsBQ5gKtkj++jYTAYEds9Ocg@mail.gmail.com>
Subject: Re: [PATCH] drm/msm/gem: Add metadata
To:     Rob Clark <robdclark@gmail.com>
Cc:     dri-devel@lists.freedesktop.org, freedreno@lists.freedesktop.org,
        linux-arm-msm@vger.kernel.org, Rob Clark <robdclark@chromium.org>,
        Abhinav Kumar <quic_abhinavk@quicinc.com>,
        Sean Paul <sean@poorly.run>,
        Marijn Suijten <marijn.suijten@somainline.org>,
        David Airlie <airlied@gmail.com>,
        Daniel Vetter <daniel@ffwll.ch>,
        open list <linux-kernel@vger.kernel.org>
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Precedence: bulk

On Fri, 27 Oct 2023 at 22:45, Rob Clark <robdclark@gmail.com> wrote:
>
> From: Rob Clark <robdclark@chromium.org>
>
> The EXT_external_objects extension is a bit awkward as it doesn't pass
> explicit modifiers, leaving the importer to guess with incomplete
> information.  In the case of vk (turnip) exporting and gl (freedreno)
> importing, the "OPTIMAL_TILING_EXT" layout depends on VkImageCreateInfo
> flags (among other things), which the importer does not know.  Which
> unfortunately leaves us with the need for a metadata back-channel.
>
> The contents of the metadata are defined by userspace.  The
> EXT_external_objects extension is only required to work between
> compatible versions of gl and vk drivers, as defined by device and
> driver UUIDs.
>
> Signed-off-by: Rob Clark <robdclark@chromium.org>
> ---
>  drivers/gpu/drm/msm/msm_drv.c | 59 +++++++++++++++++++++++++++++++++--
>  drivers/gpu/drm/msm/msm_gem.h |  4 +++
>  include/uapi/drm/msm_drm.h    |  2 ++
>  3 files changed, 63 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/msm/msm_drv.c b/drivers/gpu/drm/msm/msm_drv.c
> index b61ccea05327..8fe2677ea37a 100644
> --- a/drivers/gpu/drm/msm/msm_drv.c
> +++ b/drivers/gpu/drm/msm/msm_drv.c
> @@ -37,9 +37,10 @@
>   * - 1.9.0 - Add MSM_SUBMIT_FENCE_SN_IN
>   * - 1.10.0 - Add MSM_SUBMIT_BO_NO_IMPLICIT
>   * - 1.11.0 - Add wait boost (MSM_WAIT_FENCE_BOOST, MSM_PREP_BOOST)
> + * - 1.12.0 - Add MSM_INFO_SET_METADATA and MSM_INFO_GET_METADATA
>   */
>  #define MSM_VERSION_MAJOR      1
> -#define MSM_VERSION_MINOR      10
> +#define MSM_VERSION_MINOR      12
>  #define MSM_VERSION_PATCHLEVEL 0
>
>  static void msm_deinit_vram(struct drm_device *ddev);
> @@ -566,6 +567,8 @@ static int msm_ioctl_gem_info(struct drm_device *dev, void *data,
>                 break;
>         case MSM_INFO_SET_NAME:
>         case MSM_INFO_GET_NAME:
> +       case MSM_INFO_SET_METADATA:
> +       case MSM_INFO_GET_METADATA:
>                 break;
>         default:
>                 return -EINVAL;
> @@ -618,7 +621,7 @@ static int msm_ioctl_gem_info(struct drm_device *dev, void *data,
>                 break;
>         case MSM_INFO_GET_NAME:
>                 if (args->value && (args->len < strlen(msm_obj->name))) {
> -                       ret = -EINVAL;
> +                       ret = -ETOOSMALL;

This is unrelated and it also slightly changes user interface, so it
IMO should come as a separate commit/

>                         break;
>                 }
>                 args->len = strlen(msm_obj->name);
> @@ -627,6 +630,58 @@ static int msm_ioctl_gem_info(struct drm_device *dev, void *data,
>                                          msm_obj->name, args->len))
>                                 ret = -EFAULT;
>                 }
> +               break;
> +       case MSM_INFO_SET_METADATA:
> +               /* Impose a moderate upper bound on metadata size: */
> +               if (args->len > 128) {
> +                       ret = -EOVERFLOW;
> +                       break;
> +               }
> +
> +               ret = msm_gem_lock_interruptible(obj);
> +               if (ret)
> +                       break;
> +
> +               msm_obj->metadata =
> +                       krealloc(msm_obj->metadata, args->len, GFP_KERNEL);
> +               msm_obj->metadata_size = args->len;
> +
> +               if (copy_from_user(msm_obj->metadata, u64_to_user_ptr(args->value),
> +                                  args->len)) {
> +                       msm_obj->metadata_size = 0;
> +                       ret = -EFAULT;
> +               }
> +
> +               msm_gem_unlock(obj);
> +
> +               break;
> +       case MSM_INFO_GET_METADATA:
> +               if (!args->value) {
> +                       /*
> +                        * Querying the size is inherently racey, but
> +                        * EXT_external_objects expects the app to confirm
> +                        * via device and driver UUIDs that the exporter and
> +                        * importer versions match.  All we can do from the
> +                        * kernel side is check the length under obj lock
> +                        * when userspace tries to retrieve the metadata
> +                        */
> +                       args->len = msm_obj->metadata_size;
> +                       break;
> +               }
> +
> +               ret = msm_gem_lock_interruptible(obj);
> +               if (ret)
> +                       break;
> +
> +               if (args->len < msm_obj->metadata_size) {
> +                       ret = -ETOOSMALL;
> +               } else if (copy_to_user(u64_to_user_ptr(args->value),
> +                                       msm_obj->metadata, args->len)) {
> +                       ret = -EFAULT;
> +               }

Doesn't checkpwatch warn here about extra curly brackets?

> +
> +               msm_gem_unlock(obj);
> +
>                 break;
>         }
>
> diff --git a/drivers/gpu/drm/msm/msm_gem.h b/drivers/gpu/drm/msm/msm_gem.h
> index 7f34263048a3..8d414b072c29 100644
> --- a/drivers/gpu/drm/msm/msm_gem.h
> +++ b/drivers/gpu/drm/msm/msm_gem.h
> @@ -109,6 +109,10 @@ struct msm_gem_object {
>
>         char name[32]; /* Identifier to print for the debugfs files */
>
> +       /* userspace metadata backchannel */
> +       void *metadata;
> +       u32 metadata_size;
> +
>         /**
>          * pin_count: Number of times the pages are pinned
>          *
> diff --git a/include/uapi/drm/msm_drm.h b/include/uapi/drm/msm_drm.h
> index 6c34272a13fd..6f2a7ad04aa4 100644
> --- a/include/uapi/drm/msm_drm.h
> +++ b/include/uapi/drm/msm_drm.h
> @@ -139,6 +139,8 @@ struct drm_msm_gem_new {
>  #define MSM_INFO_GET_NAME      0x03   /* get debug name, returned by pointer */
>  #define MSM_INFO_SET_IOVA      0x04   /* set the iova, passed by value */
>  #define MSM_INFO_GET_FLAGS     0x05   /* get the MSM_BO_x flags */
> +#define MSM_INFO_SET_METADATA  0x06   /* set userspace metadata */
> +#define MSM_INFO_GET_METADATA  0x07   /* get userspace metadata */
>
>  struct drm_msm_gem_info {
>         __u32 handle;         /* in */
> --
> 2.41.0
>


-- 
With best wishes
Dmitry