linux-kernel - Re: [PATCH v3] phy/qcom-qmp-combo: propagate correct return value at phy_power

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Date: Wed, 3 Apr 2024 13:04:41 -0700
From: Stephen Boyd <swboyd@...omium.org>
To: Abhinav Kumar <quic_abhinavk@...cinc.com>, Kuogee Hsieh <quic_khsieh@...cinc.com>, 
	abel.vesa@...aro.org, agross@...nel.org, airlied@...il.com, 
	andersson@...nel.org, daniel@...ll.ch, dianders@...omium.org, 
	dmitry.baryshkov@...aro.org, dri-devel@...ts.freedesktop.org, 
	robdclark@...il.com, sean@...rly.run, vkoul@...nel.org
Cc: quic_jesszhan@...cinc.com, quic_sbillaka@...cinc.com, 
	marijn.suijten@...ainline.org, freedreno@...ts.freedesktop.org, 
	linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] phy/qcom-qmp-combo: propagate correct return value at phy_power_on()

Quoting Abhinav Kumar (2024-04-03 12:58:50)
>
>
> On 4/3/2024 12:51 PM, Stephen Boyd wrote:
> > Quoting Kuogee Hsieh (2024-03-29 12:50:35)
> >> Currently qmp_combo_dp_power_on() always return 0 in regardless of
> >> return value of cfg->configure_dp_phy(). This patch propagate
> >> return value of cfg->configure_dp_phy() all the way back to caller.
> >
> > Is this found via code inspection or because the phy is failing to power
> > on sometimes? I ask because I'm looking at a DP bug on Trogdor with
> > chromeos' v6.6 based kernel and wondering if this is related.
> >
>
> No, we actually hit an issue. This issue was originally reported as a
> link training issue while bringing up DP on x1e80100.
>
> While debugging that we noticed that we should not have even proceeded
> to link training because the PLL was not getting locked and it was
> failing silently since there are no other error prints (and hence the
> second part of the patch to improve the error logs), and we do not
> return any error code from this driver, we could not catch the PLL
> unlocked issue.

Did link training succeed in that case and the screen was black? Also,
did you figure out why the PLL failed to lock? I sometimes see reports
now with an "Unexpected interrupt:" message from the DP driver and the
interrupt is the PLL unlocked one (DP_INTR_PLL_UNLOCKED).

>
> > Also, is the call to phy_power_on() going to be checked in
> > the DP driver?
> >
> >   $ git grep -n phy_power_on -- drivers/gpu/drm/msm/dp/
> >   drivers/gpu/drm/msm/dp/dp_ctrl.c:1453:  phy_power_on(phy);
>
> Yes, this is a good point. We should also post the patch to add the
> error checking in DP driver to fail if phy_power_on fails.

Sounds great, thanks.