Re: [PATCH v3 8/8] drm/panfrost: Remove unnecessary hwaccess_lock spin_lock

From: Steven Price <steven.price@arm.com>
To: Rob Herring <robh@kernel.org>, dri-devel@lists.freedesktop.org
Cc: David Airlie <airlied@linux.ie>,
	Robin Murphy <robin.murphy@arm.com>,
	Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>,
	Tomeu Vizoso <tomeu.vizoso@collabora.com>
Subject: Re: [PATCH v3 8/8] drm/panfrost: Remove unnecessary hwaccess_lock spin_lock
Date: Wed, 28 Aug 2019 11:59:26 +0100	[thread overview]
Message-ID: <72a3950b-8daf-224c-2b0a-21cac72cc5c0@arm.com> (raw)
In-Reply-To: <20190826223317.28509-9-robh@kernel.org>

On 26/08/2019 23:33, Rob Herring wrote:
> With the introduction of the as_lock to serialize address space registers,
> the hwaccess_lock is only used within the job code and is not protecting
> anything. panfrost_job_hw_submit() only accesses registers for 1 job slot
> and it's already serialized by drm_sched.
> 
> Fixes: 7282f7645d06 ("drm/panfrost: Implement per FD address spaces")
> Cc: Tomeu Vizoso <tomeu.vizoso@collabora.com>
> Cc: Steven Price <steven.price@arm.com>
> Cc: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
> Cc: David Airlie <airlied@linux.ie>
> Cc: Daniel Vetter <daniel@ffwll.ch>
> Signed-off-by: Rob Herring <robh@kernel.org>

Reviewed-by: Steven Price <steven.price@arm.com>

Steve

> ---
> v3:
>  - New patch
> 
>  drivers/gpu/drm/panfrost/panfrost_device.c | 1 -
>  drivers/gpu/drm/panfrost/panfrost_device.h | 2 --
>  drivers/gpu/drm/panfrost/panfrost_job.c    | 4 ----
>  3 files changed, 7 deletions(-)
> 
> diff --git a/drivers/gpu/drm/panfrost/panfrost_device.c b/drivers/gpu/drm/panfrost/panfrost_device.c
> index 73805210834e..46b0b02e4289 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_device.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_device.c
> @@ -124,7 +124,6 @@ int panfrost_device_init(struct panfrost_device *pfdev)
>  	INIT_LIST_HEAD(&pfdev->scheduled_jobs);
>  	INIT_LIST_HEAD(&pfdev->as_lru_list);
> 
> -	spin_lock_init(&pfdev->hwaccess_lock);
>  	spin_lock_init(&pfdev->as_lock);
> 
>  	err = panfrost_clk_init(pfdev);
> diff --git a/drivers/gpu/drm/panfrost/panfrost_device.h b/drivers/gpu/drm/panfrost/panfrost_device.h
> index b7fa08ed3a23..9c39b9794811 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_device.h
> +++ b/drivers/gpu/drm/panfrost/panfrost_device.h
> @@ -63,8 +63,6 @@ struct panfrost_device {
>  	struct drm_device *ddev;
>  	struct platform_device *pdev;
> 
> -	spinlock_t hwaccess_lock;
> -
>  	void __iomem *iomem;
>  	struct clk *clock;
>  	struct clk *bus_clock;
> diff --git a/drivers/gpu/drm/panfrost/panfrost_job.c b/drivers/gpu/drm/panfrost/panfrost_job.c
> index 18bcc9bac6d2..a58551668d9a 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_job.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_job.c
> @@ -141,7 +141,6 @@ static void panfrost_job_write_affinity(struct panfrost_device *pfdev,
>  static void panfrost_job_hw_submit(struct panfrost_job *job, int js)
>  {
>  	struct panfrost_device *pfdev = job->pfdev;
> -	unsigned long flags;
>  	u32 cfg;
>  	u64 jc_head = job->jc;
>  	int ret;
> @@ -158,7 +157,6 @@ static void panfrost_job_hw_submit(struct panfrost_job *job, int js)
>  	cfg = panfrost_mmu_as_get(pfdev, &job->file_priv->mmu);
> 
>  	panfrost_devfreq_record_transition(pfdev, js);
> -	spin_lock_irqsave(&pfdev->hwaccess_lock, flags);
> 
>  	job_write(pfdev, JS_HEAD_NEXT_LO(js), jc_head & 0xFFFFFFFF);
>  	job_write(pfdev, JS_HEAD_NEXT_HI(js), jc_head >> 32);
> @@ -187,8 +185,6 @@ static void panfrost_job_hw_submit(struct panfrost_job *job, int js)
>  				job, js, jc_head);
> 
>  	job_write(pfdev, JS_COMMAND_NEXT(js), JS_COMMAND_START);
> -
> -	spin_unlock_irqrestore(&pfdev->hwaccess_lock, flags);
>  }
> 
>  static void panfrost_acquire_object_fences(struct drm_gem_object **bos,
> --
> 2.20.1
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