linux-kernel - Re: [PATCH v2 1/1] drm/ttm: allocate dummy_read

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Date: Wed, 17 Jan 2024 09:39:42 +0100
From: Christian König <christian.koenig@....com>
To: Yangyu Chen <cyy@...self.name>, dri-devel@...ts.freedesktop.org
Cc: linux-kernel@...r.kernel.org, Huang Rui <ray.huang@....com>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>,
 David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>,
 Jiuyang Liu <liu@...yang.me>, Yichuan Gao <i@...is.me>,
 Icenowy Zheng <uwu@...nowy.me>
Subject: Re: [PATCH v2 1/1] drm/ttm: allocate dummy_read_page without DMA32 on
 fail

Am 16.01.24 um 19:50 schrieb Yangyu Chen:
> Some platforms may not have any memory in ZONE_DMA32 and use IOMMU to allow
> 32-bit-DMA-only device to work. Forcing GFP_DMA32 on dummy_read_page will
> fail on such platforms. Retry after fail will get this works on such
> platforms.
>
> Signed-off-by: Yangyu Chen <cyy@...self.name>

Reviewed and pushed to drm-misc-fixes. That patch should show up in the 
next rc and stable kernels next week or so.

Thanks,
Christian.


> ---
>   drivers/gpu/drm/ttm/ttm_device.c | 12 +++++++++---
>   1 file changed, 9 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/ttm/ttm_device.c b/drivers/gpu/drm/ttm/ttm_device.c
> index d48b39132b32..c9fa8561f71f 100644
> --- a/drivers/gpu/drm/ttm/ttm_device.c
> +++ b/drivers/gpu/drm/ttm/ttm_device.c
> @@ -95,11 +95,17 @@ static int ttm_global_init(void)
>   	ttm_pool_mgr_init(num_pages);
>   	ttm_tt_mgr_init(num_pages, num_dma32);
>   
> -	glob->dummy_read_page = alloc_page(__GFP_ZERO | GFP_DMA32);
> +	glob->dummy_read_page = alloc_page(__GFP_ZERO | GFP_DMA32 |
> +					   __GFP_NOWARN);
>   
> +	/* Retry without GFP_DMA32 for platforms DMA32 is not available */
>   	if (unlikely(glob->dummy_read_page == NULL)) {
> -		ret = -ENOMEM;
> -		goto out;
> +		glob->dummy_read_page = alloc_page(__GFP_ZERO);
> +		if (unlikely(glob->dummy_read_page == NULL)) {
> +			ret = -ENOMEM;
> +			goto out;
> +		}
> +		pr_warn("Using GFP_DMA32 fallback for dummy_read_page\n");
>   	}
>   
>   	INIT_LIST_HEAD(&glob->device_list);