linux-kernel - Re: [PATCH 2/3] ARM: qcom_defconfig: enable MSM IOMMU for display

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Date:   Mon, 27 Nov 2017 09:48:43 -0500
From:   Rob Clark <robdclark@...il.com>
To:     Jonathan Neuschäfer <j.neuschaefer@....net>
Cc:     Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        Andy Gross <andy.gross@...aro.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/3] ARM: qcom_defconfig: enable MSM IOMMU for display

On Mon, Nov 27, 2017 at 9:34 AM, Jonathan Neuschäfer
<j.neuschaefer@....net> wrote:
> Hi,
>
> On Mon, Nov 27, 2017 at 11:44:57AM +0000, srinivas.kandagatla@...aro.org wrote:
>> From: Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
>>
>> MSM IOMMU is required for apq8064 display, so enable it by default.
>
> What exactly do you mean by "display"? Which ip block requires IOMMU
> support?
>

display block in apq8064 is mdp4 (drivers/gpu/drm/msm/mdp/mdp4)..
technically it can use iommu in bypass mode w/ physically contiguous
memory, but no one wants to do that, if they don't have to.  The gpu
does have a hard requirement on iommu.

BR,
-R