linux-kernel - Re: [PATCH v5 4/6] drm/sprd: add Unisoc's drm display controller driver

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Date:   Mon, 17 May 2021 17:35:23 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Joerg Roedel <joro@...tes.org>, Kevin Tang <kevin3.tang@...il.com>
Cc:     Maxime Ripard <maxime@...no.tech>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Sean Paul <sean@...rly.run>, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Orson Zhai <orsonzhai@...il.com>,
        Chunyan Zhang <zhang.lyra@...il.com>,
        "Linux-Kernel@...r. Kernel. Org" <linux-kernel@...r.kernel.org>,
        ML dri-devel <dri-devel@...ts.freedesktop.org>,
        devicetree@...r.kernel.org
Subject: Re: [PATCH v5 4/6] drm/sprd: add Unisoc's drm display controller
 driver

On 2021-05-17 10:27, Joerg Roedel wrote:
> On Fri, Apr 30, 2021 at 08:20:10PM +0800, Kevin Tang wrote:
>> Cc  Robin & Joerg
> 
> This is just some GPU internal MMU being used here, it seems. It doesn't
> use the IOMMU core code, so no Ack needed from the IOMMU side.

Except the actual MMU being used is drivers/iommu/sprd_iommu.c - this is 
just the display driver poking directly at the interrupt registers of 
its associated IOMMU instance. I still think this is wrong, and that it 
should be treated as a shared interrupt, with the IOMMU driver handling 
its own registers and reporting to the client through the standard 
report_iommu_fault() API, especially since there are apparently more 
blocks using these IOMMU instances than just the display.

Robin.