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

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Message-ID: <CAA8EJppCxfrBcctaR2jOrwPuO8ZFQw9vmi-0CH_sSWBm3ts7JQ@mail.gmail.com>
Date: Sat, 4 May 2024 17:23:20 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: "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>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: 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 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

-- 
With best wishes
Dmitry