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 17:15:45 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: Dmitry Baryshkov <dmitry.baryshkov@...aro.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, 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?

thanks,

greg k-h