linux-kernel - Re: [PATCH] drm/rockchip: Check iommu itself instead of it's parent for device_is

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Message-ID: <66fb4977-4e6f-f7ed-0dac-18710ebd782a@arm.com>
Date:   Mon, 28 Jun 2021 10:54:21 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Andy Yan <andy.yan@...k-chips.com>, hjc@...k-chips.com,
        heiko@...ech.de, dri-devel@...ts.freedesktop.org,
        linux-rockchip@...ts.infradead.org
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/rockchip: Check iommu itself instead of it's parent
 for device_is_available

On 2021-06-27 09:47, Andy Yan wrote:
> When iommu itself is disabled in dts, we should
> fallback to non-iommu buffer, check iommu parent
> is meanless here.
> 
> Signed-off-by: Andy Yan <andy.yan@...k-chips.com>
> ---
> 
>   drivers/gpu/drm/rockchip/rockchip_drm_drv.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_drv.c b/drivers/gpu/drm/rockchip/rockchip_drm_drv.c
> index 212bd87c0c4a..0d20c8cc1ffa 100644
> --- a/drivers/gpu/drm/rockchip/rockchip_drm_drv.c
> +++ b/drivers/gpu/drm/rockchip/rockchip_drm_drv.c
> @@ -366,7 +366,7 @@ static int rockchip_drm_platform_of_probe(struct device *dev)
>   		}
>   
>   		iommu = of_parse_phandle(port->parent, "iommus", 0);
> -		if (!iommu || !of_device_is_available(iommu->parent)) {
> +		if (!iommu || !of_device_is_available(iommu)) {

Just wondering, could you use device_iommu_mapped() to avoid poking at 
the DT at all here, or is it that you need to check remote graph 
endpoints whose struct device may not be ready yet?

Robin.

>   			DRM_DEV_DEBUG(dev,
>   				      "no iommu attached for %pOF, using non-iommu buffers\n",
>   				      port->parent);
>