linux-kernel - Re: [PATCH 5/6] phy: qcom-qmp-combo: fix drm bridge registration

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Date: Mon, 19 Feb 2024 10:03:36 +0100
From: Neil Armstrong <neil.armstrong@...aro.org>
To: Johan Hovold <johan+linaro@...nel.org>,
 Bjorn Andersson <andersson@...nel.org>,
 Andrzej Hajda <andrzej.hajda@...el.com>, Robert Foss <rfoss@...nel.org>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>,
 David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>,
 Vinod Koul <vkoul@...nel.org>
Cc: Jonas Karlman <jonas@...boo.se>,
 Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
 Jernej Skrabec <jernej.skrabec@...il.com>,
 Konrad Dybcio <konrad.dybcio@...aro.org>,
 Kishon Vijay Abraham I <kishon@...nel.org>,
 Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
 Rob Clark <robdclark@...il.com>, Abhinav Kumar <quic_abhinavk@...cinc.com>,
 Kuogee Hsieh <quic_khsieh@...cinc.com>, freedreno@...ts.freedesktop.org,
 dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
 linux-arm-msm@...r.kernel.org, linux-phy@...ts.infradead.org,
 stable@...r.kernel.org, Bjorn Andersson <quic_bjorande@...cinc.com>
Subject: Re: [PATCH 5/6] phy: qcom-qmp-combo: fix drm bridge registration

On 17/02/2024 16:02, Johan Hovold wrote:
> Due to a long-standing issue in driver core, drivers may not probe defer
> after having registered child devices to avoid triggering a probe
> deferral loop (see fbc35b45f9f6 ("Add documentation on meaning of
> -EPROBE_DEFER")).
> 
> This could potentially also trigger a bug in the DRM bridge
> implementation which does not expect bridges to go away even if device
> links may avoid triggering this (when enabled).
> 
> Move registration of the DRM aux bridge to after looking up clocks and
> other resources.
> 
> Note that PHY creation can in theory also trigger a probe deferral when
> a 'phy' supply is used. This does not seem to affect the QMP PHY driver
> but the PHY subsystem should be reworked to address this (i.e. by
> separating initialisation and registration of the PHY).
> 
> Fixes: 35921910bbd0 ("phy: qcom: qmp-combo: switch to DRM_AUX_BRIDGE")
> Fixes: 1904c3f578dc ("phy: qcom-qmp-combo: Introduce drm_bridge")
> Cc: stable@...r.kernel.org      # 6.5
> Cc: Bjorn Andersson <quic_bjorande@...cinc.com>
> Cc: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
> Signed-off-by: Johan Hovold <johan+linaro@...nel.org>
> ---
>   drivers/phy/qualcomm/phy-qcom-qmp-combo.c | 8 ++++----
>   1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/phy/qualcomm/phy-qcom-qmp-combo.c b/drivers/phy/qualcomm/phy-qcom-qmp-combo.c
> index 1ad10110dd25..e19d6a084f10 100644
> --- a/drivers/phy/qualcomm/phy-qcom-qmp-combo.c
> +++ b/drivers/phy/qualcomm/phy-qcom-qmp-combo.c
> @@ -3566,10 +3566,6 @@ static int qmp_combo_probe(struct platform_device *pdev)
>   	if (ret)
>   		return ret;
>   
> -	ret = drm_aux_bridge_register(dev);
> -	if (ret)
> -		return ret;
> -
>   	/* Check for legacy binding with child nodes. */
>   	usb_np = of_get_child_by_name(dev->of_node, "usb3-phy");
>   	if (usb_np) {
> @@ -3589,6 +3585,10 @@ static int qmp_combo_probe(struct platform_device *pdev)
>   	if (ret)
>   		goto err_node_put;
>   
> +	ret = drm_aux_bridge_register(dev);
> +	if (ret)
> +		goto err_node_put;
> +
>   	pm_runtime_set_active(dev);
>   	ret = devm_pm_runtime_enable(dev);
>   	if (ret)

Reviewed-by: Neil Armstrong <neil.armstrong@...aro.org>