linux-kernel - Re: [PATCH] drm/msm: Add MSM_SUBMIT_BO_NO

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Message-ID: <Y7bHcRAvk6GgMi5F@phenom.ffwll.local>
Date:   Thu, 5 Jan 2023 13:49:53 +0100
From:   Daniel Vetter <daniel@...ll.ch>
To:     Rob Clark <robdclark@...il.com>
Cc:     dri-devel@...ts.freedesktop.org, freedreno@...ts.freedesktop.org,
        linux-arm-msm@...r.kernel.org, Chia-I Wu <olvaffe@...il.com>,
        Rob Clark <robdclark@...omium.org>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Sean Paul <sean@...rly.run>, David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drm/msm: Add MSM_SUBMIT_BO_NO_IMPLICIT

On Tue, Dec 06, 2022 at 11:21:23AM -0800, Rob Clark wrote:
> From: Rob Clark <robdclark@...omium.org>
> 
> In cases where implicit sync is used, it is still useful (for things
> like sub-allocation, etc) to allow userspace to opt-out of implicit
> sync on per-BO basis.
> 
> Signed-off-by: Rob Clark <robdclark@...omium.org>
> ---
>  drivers/gpu/drm/msm/msm_drv.c        |  3 ++-
>  drivers/gpu/drm/msm/msm_gem_submit.c | 11 +++++++++++
>  include/uapi/drm/msm_drm.h           |  4 +++-
>  3 files changed, 16 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/msm/msm_drv.c b/drivers/gpu/drm/msm/msm_drv.c
> index 017a512982a2..e0e1199a822f 100644
> --- a/drivers/gpu/drm/msm/msm_drv.c
> +++ b/drivers/gpu/drm/msm/msm_drv.c
> @@ -45,9 +45,10 @@
>   * - 1.7.0 - Add MSM_PARAM_SUSPENDS to access suspend count
>   * - 1.8.0 - Add MSM_BO_CACHED_COHERENT for supported GPUs (a6xx)
>   * - 1.9.0 - Add MSM_SUBMIT_FENCE_SN_IN
> + * - 1.10.0 - Add MSM_SUBMIT_BO_NO_IMPLICIT
>   */
>  #define MSM_VERSION_MAJOR	1
> -#define MSM_VERSION_MINOR	9
> +#define MSM_VERSION_MINOR	10
>  #define MSM_VERSION_PATCHLEVEL	0
>  
>  static const struct drm_mode_config_funcs mode_config_funcs = {
> diff --git a/drivers/gpu/drm/msm/msm_gem_submit.c b/drivers/gpu/drm/msm/msm_gem_submit.c
> index eb3536e3d66a..8bad07a04f85 100644
> --- a/drivers/gpu/drm/msm/msm_gem_submit.c
> +++ b/drivers/gpu/drm/msm/msm_gem_submit.c
> @@ -334,9 +334,20 @@ static int submit_fence_sync(struct msm_gem_submit *submit, bool no_implicit)
>  		if (ret)
>  			return ret;
>  
> +		/* If userspace has determined that explicit fencing is
> +		 * used, it can disable implicit sync on the entire
> +		 * submit:
> +		 */
>  		if (no_implicit)
>  			continue;
>  
> +		/* Otherwise userspace can ask for implicit sync to be
> +		 * disabled on specific buffers.  This is useful for internal
> +		 * usermode driver managed buffers, suballocation, etc.
> +		 */
> +		if (submit->bos[i].flags & MSM_SUBMIT_BO_NO_IMPLICIT)
> +			continue;
> +
>  		ret = drm_sched_job_add_implicit_dependencies(&submit->base,

Won't this break shrinkers and fun stuff like that? It's why we added the
new USAGE_OTHER fence slot at least, and also why I wonder whether we
shouldn't push this into the helper to make the right call. Every driver
kinda needs the same wheel.
-Daniel

>  							      obj,
>  							      write);
> diff --git a/include/uapi/drm/msm_drm.h b/include/uapi/drm/msm_drm.h
> index f54b48ef6a2d..329100016e7c 100644
> --- a/include/uapi/drm/msm_drm.h
> +++ b/include/uapi/drm/msm_drm.h
> @@ -222,10 +222,12 @@ struct drm_msm_gem_submit_cmd {
>  #define MSM_SUBMIT_BO_READ             0x0001
>  #define MSM_SUBMIT_BO_WRITE            0x0002
>  #define MSM_SUBMIT_BO_DUMP             0x0004
> +#define MSM_SUBMIT_BO_NO_IMPLICIT      0x0008
>  
>  #define MSM_SUBMIT_BO_FLAGS            (MSM_SUBMIT_BO_READ | \
>  					MSM_SUBMIT_BO_WRITE | \
> -					MSM_SUBMIT_BO_DUMP)
> +					MSM_SUBMIT_BO_DUMP | \
> +					MSM_SUBMIT_BO_NO_IMPLICIT)
>  
>  struct drm_msm_gem_submit_bo {
>  	__u32 flags;          /* in, mask of MSM_SUBMIT_BO_x */
> -- 
> 2.38.1
> 

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