linux-kernel - Re: [PATCH] ARM: exynos_defconfig

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Date:   Thu, 14 Dec 2017 19:00:42 +0100
From:   Krzysztof Kozlowski <krzk@...nel.org>
To:     Marek Szyprowski <m.szyprowski@...sung.com>
Cc:     Shuah Khan <shuahkh@....samsung.com>, linux@...linux.org.uk,
        kgene@...nel.org, linux.amoon@...il.com, arnd@...db.de,
        javier@...hile0.org, robie@...tgohome.co.uk, shuah@...nel.org,
        viresh.kumar@...aro.org, linux-arm-kernel@...ts.infradead.org,
        linux-samsung-soc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ARM: exynos_defconfig - enable CONFIG_EXYNOS_IOMMU

On Wed, Dec 13, 2017 at 10:42:33AM +0100, Marek Szyprowski wrote:
> Hi Shuah,
> 
> On 2017-12-12 22:31, Shuah Khan wrote:
> > EXYNOS_IOMMU is disabled in exynos_defconfig since it is known to cause
> > boot failures on Exynos Chrome-books. The recommendation is for IOMMU to
> > be enabled manually on systems as needed.
> > 
> > A recent exynos_drm change added a warning message when EXYNOS_IOMMU is
> > disabled. It is necessary to enable it to avoid the warning messages.
> > A few initial tests have shown that enabling EXYNOS_IOMMU might be safe
> > on Exynos Chrome-books.
> > 
> > Enable CONFIG_EXYNOS_IOMMU in exynos_defconfig.
> > 
> > Signed-off-by: Shuah Khan <shuahkh@....samsung.com>
> 
> Due to some other changes in the order of operations during boot process,
> power domains are initialized very early and because of the temporary
> lack of devices (which are not yet added to the system), are turned off.
> 
> This practically stops FIMD for scanning framebuffer very early during
> boot, before IOMMU gets initialized and "solves" the issue, which was
> the reason to disable Exynos IOMMU by default.
> 
> Like I've already said, I've checked Exynos Snow Chromebook boots fine
> with IOMMU support enabled, both with v4.15-rc3 and linux-next.
> 
> Acked-by: Marek Szyprowski <m.szyprowski@...sung.com>
> Tested-by: Marek Szyprowski <m.szyprowski@...sung.com>

Thanks, applied with rephrased and extended message using Marek's
explanation.

Best regards,
Krzysztof