linux-kernel - Re: [PATCH v4] usb: typec: qcom-pmic-typec: split HPD bridge alloc and registration

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Date: Sat, 4 May 2024 19:54:37 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: "Bryan O'Donoghue" <bryan.odonoghue@...aro.org>, 
	Heikki Krogerus <heikki.krogerus@...ux.intel.com>, Bjorn Andersson <andersson@...nel.org>, 
	Konrad Dybcio <konrad.dybcio@...aro.org>, Johan Hovold <johan+linaro@...nel.org>, 
	linux-arm-msm@...r.kernel.org, linux-usb@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Caleb Connolly <caleb.connolly@...aro.org>
Subject: Re: [PATCH v4] usb: typec: qcom-pmic-typec: split HPD bridge alloc
 and registration

On Sat, 4 May 2024 at 19:22, Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
>
> On Sat, May 04, 2024 at 05:15:45PM +0200, Greg Kroah-Hartman wrote:
> > On Sat, May 04, 2024 at 05:23:20PM +0300, Dmitry Baryshkov wrote:
> > > On Wed, 24 Apr 2024 at 05:16, Dmitry Baryshkov
> > > <dmitry.baryshkov@...aro.org> wrote:
> > > >
> > > > If a probe function returns -EPROBE_DEFER after creating another device
> > > > there is a change of ending up in a probe deferral loop, (see commit
> > > > fbc35b45f9f6 ("Add documentation on meaning of -EPROBE_DEFER"). In case
> > > > of the qcom-pmic-typec driver the tcpm_register_port() function looks up
> > > > external resources (USB role switch and inherently via called
> > > > typec_register_port() USB-C muxes, switches and retimers).
> > > >
> > > > In order to prevent such probe-defer loops caused by qcom-pmic-typec
> > > > driver, use the API added by Johan Hovold and move HPD bridge
> > > > registration to the end of the probe function.
> > > >
> > > > The devm_drm_dp_hpd_bridge_add() is called at the end of the probe
> > > > function after all TCPM start functions. This is done as a way to
> > > > overcome a different problem, the DRM subsystem can not properly cope
> > > > with the DRM bridges being destroyed once the bridge is attached. Having
> > > > this function call at the end of the probe function prevents possible
> > > > DRM bridge device creation followed by destruction in case one of the
> > > > TCPM start functions returns an error.
> > > >
> > > > Reported-by: Caleb Connolly <caleb.connolly@...aro.org>
> > > > Acked-by: Bryan O'Donoghue <bryan.odonoghue@...aro.org>
> > > > Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
> > > > ---
> > > > Dependency: https://lore.kernel.org/lkml/20240418145730.4605-2-johan+linaro@kernel.org/
> > > > ---
> > > > Changes in v4:
> > > > - Rebased on top of Johan's patches
> > > > - Link to v3: https://lore.kernel.org/r/20240416-qc-pmic-typec-hpd-split-v3-1-fd071e3191a1@linaro.org
> > > >
> > > > Changes in v3:
> > > > - Updated commit message to explain my decisions (Johan).
> > > > - Link to v2: https://lore.kernel.org/r/20240408-qc-pmic-typec-hpd-split-v2-1-1704f5321b73@linaro.org
> > > >
> > > > Changes in v2:
> > > > - Fix commit message (Bryan)
> > > > - Link to v1: https://lore.kernel.org/r/20240405-qc-pmic-typec-hpd-split-v1-1-363daafb3c36@linaro.org
> > > > ---
> > > >  drivers/usb/typec/tcpm/qcom/qcom_pmic_typec.c | 10 ++++++++--
> > > >  1 file changed, 8 insertions(+), 2 deletions(-)
> > >
> > > A stupid gracious ping. It would be nice to fix the issue in 6.10
> >
> > Is this a regression?  If so, what commit does it fix?  Or has it always
> > just not worked?
>
> Oh wait, I need Johan's patches applied first, I was waiting for that to
> happen, so I'll take this next week when that gets into Linus's tree,
> sorry for the delay.

No problem, as long as it has a chance to land at 6.10.
Thank you!


-- 
With best wishes
Dmitry