linux-kernel - Re: [PATCH v17 2/4] drm/msm/dpu: Defer SSPP allocation until CRTC check

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Message-ID: <c56e4ylgwcqni23btaxegdbfg3tbkyp2vtjtboeb3kbvcfk27u@vrlh276djtfr>
Date: Thu, 22 Jan 2026 12:22:14 +0200
From: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
To: Jun Nie <jun.nie@...aro.org>
Cc: Abhinav Kumar <abhinav.kumar@...ux.dev>,
        Dmitry Baryshkov <lumag@...nel.org>, Sean Paul <sean@...rly.run>,
        Marijn Suijten <marijn.suijten@...ainline.org>,
        David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
        Rob Clark <robin.clark@....qualcomm.com>,
        Neil Armstrong <neil.armstrong@...aro.org>,
        linux-arm-msm@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        freedreno@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v17 2/4] drm/msm/dpu: Defer SSPP allocation until CRTC
 check

On Thu, Jan 22, 2026 at 02:03:25PM +0800, Jun Nie wrote:
> Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com> 于2026年1月21日周三 17:30写道：
> >
> > On Wed, Jan 21, 2026 at 04:01:51PM +0800, Jun Nie wrote:
> > > Currently, plane splitting and SSPP allocation occur during the plane
> > > check phase. Defer these operations until dpu_assign_plane_resources()
> > > is called from the CRTC side to ensure the topology information from
> > > the CRTC check is available.
> >
> > Why is it important? What is broken otherwise?
> 
> I see. Thanks! Will add below lines in next version.
> 
> By default, the plane check occurs before the CRTC check.
> Without topology information from the CRTC, plane splitting
> cannot be properly executed. Consequently, the SSPP
> engine starts without a valid memory address, which triggers
> an IOMMU warning.

What is plane splitting? Write commit message for somebody who doesn't
exactly know what is going on.


-- 
With best wishes
Dmitry