linux-kernel - Re: [PATCH] arm: exynos increase CONFIG_CMA_SIZE

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Date:   Tue, 28 Feb 2017 13:42:58 -0300
From:   Javier Martinez Canillas <javier@....samsung.com>
To:     Shuah Khan <shuahkh@....samsung.com>, linux@...linux.org.uk,
        kgene@...nel.org, krzk@...nel.org, arnd@...db.de,
        cw00.choi@...sung.com, rafael.j.wysocki@...el.com,
        robie@...tgohome.co.uk, b.zolnierkie@...sung.com,
        viresh.kumar@...aro.org, m.szyprowski@...sung.com,
        s.nawrocki@...sung.com, a.hajda@...sung.com, inki.dae@...sung.com,
        sw0312.kim@...sung.com
Cc:     shuah@...nel.org, linux-arm-kernel@...ts.infradead.org,
        linux-samsung-soc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm: exynos increase CONFIG_CMA_SIZE_MBYTES to 96

Hello Shuah,

The subject line isn't consistent with what's used for exynos_defconfig
changes, please use instead:

ARM: exynos_defconfig: Increase CONFIG_CMA_SIZE_MBYTES to 96

On 02/27/2017 09:23 PM, Shuah Khan wrote:
> Current CMA size of 64 Mbytes is right on the edge of being too small
> for some display managers.  With the proposed s5p_mfc patch series that
> pre-allocate buffers, when display manager starts, it fails to get GEM
> buffers.  Increasing the CMA size to 96 solves the problem.
>
> Change CONFIG_CMA_SIZE_MBYTES to 96 in exynos_defconfig to address the
> problem.
>

As you mention, the problem is when a driver pre-allocates a lot of CMA
memory. So instead of mentioning an in-flight patch series, I would make
the commit message more generic. Something along the following lines:

Current CMA size is 64 Mbytes, but this may not be enough if different
drivers need to allocate big memory chunks.

For example, the s5p-mfc driver may need to do a pre-allocation of N MiB
to decode a H.264 1080p video, and there won't be enough CMA memory left
for others drivers, like the exynos-drm driver that may need to allocate
GEM buffers for the display manager.

Increasing the CMA size to 96 MiB should be enough for most use cases.

> Signed-off-by: Shuah Khan <shuahkh@....samsung.com>
> Suggested-by: Marek Szyprowski <m.szyprowski@...sung.com>
> ---

Patch looks good to me though.

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

Best regards,
-- 
Javier Martinez Canillas
Open Source Group
Samsung Research America