linux-kernel - Re: [PATCH 2/3] drm/panthor: Explicitly set the coherency mode

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Message-ID: <5673689c-28cd-4fc5-a627-4858ebe9face@arm.com>
Date: Fri, 25 Oct 2024 11:03:35 +0100
From: Steven Price <steven.price@....com>
To: Akash Goel <akash.goel@....com>, boris.brezillon@...labora.com,
 liviu.dudau@....com
Cc: dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
 mihail.atanassov@....com, ketil.johnsen@....com, florent.tomasin@....com,
 maarten.lankhorst@...ux.intel.com, mripard@...nel.org, tzimmermann@...e.de,
 airlied@...il.com, daniel@...ll.ch, nd@....com
Subject: Re: [PATCH 2/3] drm/panthor: Explicitly set the coherency mode

On 24/10/2024 15:54, Akash Goel wrote:
> This commit fixes the potential misalignment between the value of device
> tree property "dma-coherent" and default value of COHERENCY_ENABLE
> register.
> Panthor driver didn't explicitly program the COHERENCY_ENABLE register
> with the desired coherency mode. The default value of COHERENCY_ENABLE
> register is implementation defined, so it may not be always aligned with
> the "dma-coherent" property value.
> The commit also checks the COHERENCY_FEATURES register to confirm that
> the coherency protocol is actually supported or not.
> 
> Signed-off-by: Akash Goel <akash.goel@....com>

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

> ---
>  drivers/gpu/drm/panthor/panthor_device.c | 22 +++++++++++++++++++++-
>  drivers/gpu/drm/panthor/panthor_gpu.c    |  9 +++++++++
>  2 files changed, 30 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/panthor/panthor_device.c b/drivers/gpu/drm/panthor/panthor_device.c
> index 4082c8f2951d..984615f4ed27 100644
> --- a/drivers/gpu/drm/panthor/panthor_device.c
> +++ b/drivers/gpu/drm/panthor/panthor_device.c
> @@ -22,6 +22,24 @@
>  #include "panthor_regs.h"
>  #include "panthor_sched.h"
>  
> +static int panthor_gpu_coherency_init(struct panthor_device *ptdev)
> +{
> +	ptdev->coherent = device_get_dma_attr(ptdev->base.dev) == DEV_DMA_COHERENT;
> +
> +	if (!ptdev->coherent)
> +		return 0;
> +
> +	/* Check if the ACE-Lite coherency protocol is actually supported by the GPU.
> +	 * ACE protocol has never been supported for command stream frontend GPUs.
> +	 */
> +	if ((gpu_read(ptdev, GPU_COHERENCY_FEATURES) &
> +		      GPU_COHERENCY_PROT_BIT(ACE_LITE)))
> +		return 0;
> +
> +	drm_err(&ptdev->base, "Coherency not supported by the device");
> +	return -ENOTSUPP;
> +}
> +
>  static int panthor_clk_init(struct panthor_device *ptdev)
>  {
>  	ptdev->clks.core = devm_clk_get(ptdev->base.dev, NULL);
> @@ -156,7 +174,9 @@ int panthor_device_init(struct panthor_device *ptdev)
>  	struct page *p;
>  	int ret;
>  
> -	ptdev->coherent = device_get_dma_attr(ptdev->base.dev) == DEV_DMA_COHERENT;
> +	ret = panthor_gpu_coherency_init(ptdev);
> +	if (ret)
> +		return ret;
>  
>  	init_completion(&ptdev->unplug.done);
>  	ret = drmm_mutex_init(&ptdev->base, &ptdev->unplug.lock);
> diff --git a/drivers/gpu/drm/panthor/panthor_gpu.c b/drivers/gpu/drm/panthor/panthor_gpu.c
> index 5251d8764e7d..1e24f08a519a 100644
> --- a/drivers/gpu/drm/panthor/panthor_gpu.c
> +++ b/drivers/gpu/drm/panthor/panthor_gpu.c
> @@ -77,6 +77,12 @@ static const struct panthor_model gpu_models[] = {
>  	 GPU_IRQ_RESET_COMPLETED | \
>  	 GPU_IRQ_CLEAN_CACHES_COMPLETED)
>  
> +static void panthor_gpu_coherency_set(struct panthor_device *ptdev)
> +{
> +	gpu_write(ptdev, GPU_COHERENCY_PROTOCOL,
> +		ptdev->coherent ? GPU_COHERENCY_PROT_BIT(ACE_LITE) : GPU_COHERENCY_NONE);
> +}
> +
>  static void panthor_gpu_init_info(struct panthor_device *ptdev)
>  {
>  	const struct panthor_model *model;
> @@ -365,6 +371,9 @@ int panthor_gpu_l2_power_on(struct panthor_device *ptdev)
>  			      hweight64(ptdev->gpu_info.shader_present));
>  	}
>  
> +	/* Set the desired coherency mode before the power up of L2 */
> +	panthor_gpu_coherency_set(ptdev);
> +
>  	return panthor_gpu_power_on(ptdev, L2, 1, 20000);
>  }
>