Re: [PATCH] drm/panthor: Don't use virt_to_pfn()

From: Robin Murphy <robin.murphy@arm.com>
To: Steven Price <steven.price@arm.com>,
	Boris Brezillon <boris.brezillon@collabora.com>,
	Liviu Dudau <liviu.dudau@arm.com>
Cc: dri-devel@lists.freedesktop.org
Subject: Re: [PATCH] drm/panthor: Don't use virt_to_pfn()
Date: Mon, 18 Mar 2024 15:11:42 +0000	[thread overview]
Message-ID: <5566e7e4-7c35-4939-9676-a739c96b8aa5@arm.com> (raw)
In-Reply-To: <20240318145119.368582-1-steven.price@arm.com>

On 18/03/2024 2:51 pm, Steven Price wrote:
> virt_to_pfn() isn't available on x86 (except to xen) so breaks
> COMPILE_TEST builds. Avoid its use completely by instead storing the
> struct page pointer allocated in panthor_device_init() and using
> page_to_pfn() instead.
> 
> Signed-off-by: Steven Price <steven.price@arm.com>
> ---
>   drivers/gpu/drm/panthor/panthor_device.c | 10 ++++++----
>   drivers/gpu/drm/panthor/panthor_device.h |  2 +-
>   2 files changed, 7 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/gpu/drm/panthor/panthor_device.c b/drivers/gpu/drm/panthor/panthor_device.c
> index 69deb8e17778..3c30da03fa48 100644
> --- a/drivers/gpu/drm/panthor/panthor_device.c
> +++ b/drivers/gpu/drm/panthor/panthor_device.c
> @@ -154,6 +154,7 @@ int panthor_device_init(struct panthor_device *ptdev)
>   {
>   	struct resource *res;
>   	struct page *p;
> +	u32 *dummy_page_virt;
>   	int ret;
>   
>   	ptdev->coherent = device_get_dma_attr(ptdev->base.dev) == DEV_DMA_COHERENT;
> @@ -172,9 +173,10 @@ int panthor_device_init(struct panthor_device *ptdev)
>   	if (!p)
>   		return -ENOMEM;
>   
> -	ptdev->pm.dummy_latest_flush = page_address(p);
> +	ptdev->pm.dummy_latest_flush = p;
> +	dummy_page_virt = page_address(p);
>   	ret = drmm_add_action_or_reset(&ptdev->base, panthor_device_free_page,
> -				       ptdev->pm.dummy_latest_flush);
> +				       dummy_page_virt);

Nit: I was about to say I'd be inclined to switch the callback to 
__free_page() instead, but then I realise there's no real need to be 
reinventing that in the first place:

	dummy_page_virt = (void *)devm_get_free_pages(ptdev->base.dev,
					GFP_KERNEL | GFP_ZERO, 0);
	if (!dummy_page_virt)
		return -ENOMEM;

	ptdev->pm.dummy_latest_flush = virt_to_page(dummy_page_virt);

Cheers,
Robin.

>   	if (ret)
>   		return ret;
>   
> @@ -184,7 +186,7 @@ int panthor_device_init(struct panthor_device *ptdev)
>   	 * happens while the dummy page is mapped. Zero cannot be used because
>   	 * that means 'always flush'.
>   	 */
> -	*ptdev->pm.dummy_latest_flush = 1;
> +	*dummy_page_virt = 1;
>   
>   	INIT_WORK(&ptdev->reset.work, panthor_device_reset_work);
>   	ptdev->reset.wq = alloc_ordered_workqueue("panthor-reset-wq", 0);
> @@ -353,7 +355,7 @@ static vm_fault_t panthor_mmio_vm_fault(struct vm_fault *vmf)
>   		if (active)
>   			pfn = __phys_to_pfn(ptdev->phys_addr + CSF_GPU_LATEST_FLUSH_ID);
>   		else
> -			pfn = virt_to_pfn(ptdev->pm.dummy_latest_flush);
> +			pfn = page_to_pfn(ptdev->pm.dummy_latest_flush);
>   		break;
>   
>   	default:
> diff --git a/drivers/gpu/drm/panthor/panthor_device.h b/drivers/gpu/drm/panthor/panthor_device.h
> index 51c9d61b6796..c84c27dcc92c 100644
> --- a/drivers/gpu/drm/panthor/panthor_device.h
> +++ b/drivers/gpu/drm/panthor/panthor_device.h
> @@ -160,7 +160,7 @@ struct panthor_device {
>   		 * Used to replace the real LATEST_FLUSH page when the GPU
>   		 * is suspended.
>   		 */
> -		u32 *dummy_latest_flush;
> +		struct page *dummy_latest_flush;
>   	} pm;
>   };
>   