linux-kernel - Re: [PATCH v4 09/11] drm/msm/A6XX: Add a flag to allow preemption to submitqueue

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Message-ID: <20240920165427.wikjsywhbcb2kz7h@hu-akhilpo-hyd.qualcomm.com>
Date: Fri, 20 Sep 2024 22:24:27 +0530
From: Akhil P Oommen <quic_akhilpo@...cinc.com>
To: Antonino Maniscalco <antomani103@...il.com>
CC: Rob Clark <robdclark@...il.com>, Sean Paul <sean@...rly.run>,
        "Konrad
 Dybcio" <konrad.dybcio@...aro.org>,
        Abhinav Kumar
	<quic_abhinavk@...cinc.com>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Marijn Suijten <marijn.suijten@...ainline.org>,
        David Airlie
	<airlied@...il.com>, "Daniel Vetter" <daniel@...ll.ch>,
        Maarten Lankhorst
	<maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Jonathan Corbet <corbet@....net>, <linux-arm-msm@...r.kernel.org>,
        <dri-devel@...ts.freedesktop.org>, <freedreno@...ts.freedesktop.org>,
        <linux-kernel@...r.kernel.org>, <linux-doc@...r.kernel.org>,
        Neil Armstrong <neil.armstrong@...aro.org>
Subject: Re: [PATCH v4 09/11] drm/msm/A6XX: Add a flag to allow preemption to
 submitqueue_create

On Tue, Sep 17, 2024 at 01:14:19PM +0200, Antonino Maniscalco wrote:
> Some userspace changes are necessary so add a flag for userspace to
> advertise support for preemption when creating the submitqueue.
> 
> When this flag is not set preemption will not be allowed in the middle
> of the submitted IBs therefore mantaining compatibility with older
> userspace.
> 
> The flag is rejected if preemption is not supported on the target, this
> allows userspace to know whether preemption is supported.

Just curious, what is the motivation behind informing userspace about
preemption support?

-Akhil

> 
> Signed-off-by: Antonino Maniscalco <antomani103@...il.com>
> Tested-by: Neil Armstrong <neil.armstrong@...aro.org> # on SM8650-QRD
> ---
>  drivers/gpu/drm/msm/adreno/a6xx_gpu.c | 12 ++++++++----
>  drivers/gpu/drm/msm/msm_submitqueue.c |  3 +++
>  include/uapi/drm/msm_drm.h            |  5 ++++-
>  3 files changed, 15 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/gpu/drm/msm/adreno/a6xx_gpu.c b/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
> index 736f475d696f..edbcb6d229ba 100644
> --- a/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
> +++ b/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
> @@ -430,8 +430,10 @@ static void a7xx_submit(struct msm_gpu *gpu, struct msm_gem_submit *submit)
>  	OUT_PKT7(ring, CP_SET_MARKER, 1);
>  	OUT_RING(ring, 0x101); /* IFPC disable */
>  
> -	OUT_PKT7(ring, CP_SET_MARKER, 1);
> -	OUT_RING(ring, 0x00d); /* IB1LIST start */
> +	if (submit->queue->flags & MSM_SUBMITQUEUE_ALLOW_PREEMPT) {
> +		OUT_PKT7(ring, CP_SET_MARKER, 1);
> +		OUT_RING(ring, 0x00d); /* IB1LIST start */
> +	}
>  
>  	/* Submit the commands */
>  	for (i = 0; i < submit->nr_cmds; i++) {
> @@ -462,8 +464,10 @@ static void a7xx_submit(struct msm_gpu *gpu, struct msm_gem_submit *submit)
>  			update_shadow_rptr(gpu, ring);
>  	}
>  
> -	OUT_PKT7(ring, CP_SET_MARKER, 1);
> -	OUT_RING(ring, 0x00e); /* IB1LIST end */
> +	if (submit->queue->flags & MSM_SUBMITQUEUE_ALLOW_PREEMPT) {
> +		OUT_PKT7(ring, CP_SET_MARKER, 1);
> +		OUT_RING(ring, 0x00e); /* IB1LIST end */
> +	}
>  
>  	get_stats_counter(ring, REG_A7XX_RBBM_PERFCTR_CP(0),
>  		rbmemptr_stats(ring, index, cpcycles_end));
> diff --git a/drivers/gpu/drm/msm/msm_submitqueue.c b/drivers/gpu/drm/msm/msm_submitqueue.c
> index 0e803125a325..9b3ffca3f3b4 100644
> --- a/drivers/gpu/drm/msm/msm_submitqueue.c
> +++ b/drivers/gpu/drm/msm/msm_submitqueue.c
> @@ -170,6 +170,9 @@ int msm_submitqueue_create(struct drm_device *drm, struct msm_file_private *ctx,
>  	if (!priv->gpu)
>  		return -ENODEV;
>  
> +	if (flags & MSM_SUBMITQUEUE_ALLOW_PREEMPT && priv->gpu->nr_rings == 1)
> +		return -EINVAL;
> +
>  	ret = msm_gpu_convert_priority(priv->gpu, prio, &ring_nr, &sched_prio);
>  	if (ret)
>  		return ret;
> diff --git a/include/uapi/drm/msm_drm.h b/include/uapi/drm/msm_drm.h
> index 3fca72f73861..f37858db34e6 100644
> --- a/include/uapi/drm/msm_drm.h
> +++ b/include/uapi/drm/msm_drm.h
> @@ -345,7 +345,10 @@ struct drm_msm_gem_madvise {
>   * backwards compatibility as a "default" submitqueue
>   */
>  
> -#define MSM_SUBMITQUEUE_FLAGS (0)
> +#define MSM_SUBMITQUEUE_ALLOW_PREEMPT	0x00000001
> +#define MSM_SUBMITQUEUE_FLAGS		    ( \
> +		MSM_SUBMITQUEUE_ALLOW_PREEMPT | \
> +		0)
>  
>  /*
>   * The submitqueue priority should be between 0 and MSM_PARAM_PRIORITIES-1,
> 
> -- 
> 2.46.0
>