linux-kernel - Re: [PATCH] exynos-drm: Fix display manager failing to start without IOMMU problem

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Date:	Thu, 11 Aug 2016 07:59:57 +0900
From:	Inki Dae <inki.dae@...sung.com>
To:	Shuah Khan <shuahkh@....samsung.com>, jy0922.shim@...sung.com,
	sw0312.kim@...sung.com, kyungmin.park@...sung.com,
	airlied@...ux.ie, kgene@...nel.org, k.kozlowski@...sung.com
Cc:	dri-devel@...ts.freedesktop.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-samsung-soc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] exynos-drm: Fix display manager failing to start without
 IOMMU problem

Hi Shuah,

2016년 08월 11일 02:30에 Shuah Khan 이(가) 쓴 글:
> Fix exynos_drm_gem_create_ioctl() attempts to allocate non-contiguous GEM
> memory without IOMMU. In this case, there is no point in attempting to

DRM gem can be used for Non-DRM drivers such as GPU, V4L2 based Multimedia device and other DMA devices.
Even though IOMMU support is disabled, other framework based DMA drivers can use IOMMU - i.e., GPU driver -
and they can use non-contiguous GEM buffer through UMM. (DMABUF) 

So GEM allocation type is not dependent on IOMMU.

Thanks,
Inki Dae

> allocate non-contiguous memory, only to return error during the next step
> from exynos_drm_framebuffer_init() which leads to display manager failing
> to start.
> 
> Check if non-contiguous GEM memory is requested without IOMMU. If so,
> allocate contiguous GEM memory to help display manager start.
> 
> Signed-off-by: Shuah Khan <shuahkh@....samsung.com>
> ---
>  drivers/gpu/drm/exynos/exynos_drm_gem.c | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
> 
> diff --git a/drivers/gpu/drm/exynos/exynos_drm_gem.c b/drivers/gpu/drm/exynos/exynos_drm_gem.c
> index 4c4cb0e..4719116 100644
> --- a/drivers/gpu/drm/exynos/exynos_drm_gem.c
> +++ b/drivers/gpu/drm/exynos/exynos_drm_gem.c
> @@ -266,6 +266,20 @@ int exynos_drm_gem_create_ioctl(struct drm_device *dev, void *data,
>  	struct exynos_drm_gem *exynos_gem;
>  	int ret;
>  
> +	/*
> +	 * Check if non-contiguous GEM memory is requested without IOMMU.
> +	 * If so, allocate contiguous GEM memory.
> +	 *
> +	 * There is no point in attempting to allocate non-contiguous memory,
> +	 * only to return error from exynos_drm_framebuffer_init() which leads
> +	 * to display manager failing to start.
> +	*/
> +	if (!is_drm_iommu_supported(dev) &&
> +	    (args->flags & EXYNOS_BO_NONCONTIG)) {
> +		args->flags &= ~EXYNOS_BO_NONCONTIG;
> +		args->flags |= EXYNOS_BO_CONTIG;
> +	}
> +
>  	exynos_gem = exynos_drm_gem_create(dev, args->flags, args->size);
>  	if (IS_ERR(exynos_gem))
>  		return PTR_ERR(exynos_gem);
>