linux-kernel - Re: [V2][PATCH] drm: xlnx: zynqmp: release reset to DP controller before accessing DP registers

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Date:   Fri, 6 Aug 2021 13:43:37 +0300
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Michal Simek <monstr@...str.eu>
Cc:     Quanyang Wang <quanyang.wang@...driver.com>,
        Hyun Kwon <hyun.kwon@...inx.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        dri-devel@...ts.freedesktop.org,
        linux-arm <linux-arm-kernel@...ts.infradead.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [V2][PATCH] drm: xlnx: zynqmp: release reset to DP controller
 before accessing DP registers

Hi Michale,

On Fri, Aug 06, 2021 at 12:37:07PM +0200, Michal Simek wrote:
> st 24. 3. 2021 v 4:15 odesílatel Laurent Pinchart napsal:
> > On Tue, Mar 23, 2021 at 10:55:01AM +0800, quanyang.wang@...driver.com wrote:
> > > From: Quanyang Wang <quanyang.wang@...driver.com>
> > >
> > > When insmod zynqmp-dpsub.ko after rmmod it, system will hang with the
> > > error log as below:
> > >
> > > root@...inx-zynqmp:~# insmod zynqmp-dpsub.ko
> > > [   88.391289] [drm] Initialized zynqmp-dpsub 1.0.0 20130509 for fd4a0000.display on minor 0
> > > [   88.529906] Console: switching to colour frame buffer device 128x48
> > > [   88.549402] zynqmp-dpsub fd4a0000.display: [drm] fb0: zynqmp-dpsubdrm frame buffer device
> > > [   88.571624] zynqmp-dpsub fd4a0000.display: ZynqMP DisplayPort Subsystem driver probed
> > > root@...inx-zynqmp:~# rmmod zynqmp_dpsub
> > > [   94.023404] Console: switching to colour dummy device 80x25
> > > root@...inx-zynqmp:~# insmod zynqmp-dpsub.ko
> > >       <hang here>
> > >
> > > This is because that in zynqmp_dp_probe it tries to access some DP
> > > registers while the DP controller is still in the reset state. When
> > > running "rmmod zynqmp_dpsub", zynqmp_dp_reset(dp, true) in
> > > zynqmp_dp_phy_exit is called to force the DP controller into the reset
> > > state. Then insmod will call zynqmp_dp_probe to program the DP registers,
> > > but at this moment the DP controller hasn't been brought out of the reset
> > > state yet since the function zynqmp_dp_reset(dp, false) is called later and
> > > this will result the system hang.
> > >
> > > Releasing the reset to DP controller before any read/write operation to it
> > > will fix this issue. And for symmetry, move zynqmp_dp_reset() call from
> > > zynqmp_dp_phy_exit() to zynqmp_dp_remove().
> > >
> > > Signed-off-by: Quanyang Wang <quanyang.wang@...driver.com>
> >
> > Reviewed-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>
> 
> Can someone pick this patch?

I have it in my tree with a set of other changes, I intend to send a
pull request today.

-- 
Regards,

Laurent Pinchart