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

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Date:	Wed, 10 Aug 2016 13:41:55 -0400
From:	Javier Martinez Canillas <javier@...hile0.org>
To:	Shuah Khan <shuahkh@....samsung.com>
Cc:	InKi Dae <inki.dae@...sung.com>,
	Joonyoung Shim <jy0922.shim@...sung.com>,
	Seung-Woo Kim <sw0312.kim@...sung.com>,
	Kyungmin Park <kyungmin.park@...sung.com>,
	David Airlie <airlied@...ux.ie>, Kukjin Kim <kgene@...nel.org>,
	Krzysztof Kozłowski <k.kozlowski@...sung.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-samsung-soc@...r.kernel.org" 
	<linux-samsung-soc@...r.kernel.org>,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] exynos-drm: Fix display manager failing to start without
 IOMMU problem

Hello Shuah,

On Wed, Aug 10, 2016 at 1:30 PM, Shuah Khan <shuahkh@....samsung.com> wrote:
> 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
> 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;
> +       }
> +

I'm not a DRM expert so I don't know if this is the correct way to
handle this. But the approach sounds sensible to me.

Reviewed-by: Javier Martinez Canillas <javier@....samsung.com>

Best regards,
Javier