linux-kernel - Re: [PATCH 2/2] drm/msm/dp: Implement oob_hotplug

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Date:   Tue, 8 Feb 2022 08:40:35 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Bjorn Andersson <bjorn.andersson@...aro.org>
Cc:     Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>,
        Rob Clark <robdclark@...il.com>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>, Sean Paul <sean@...rly.run>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Stephen Boyd <swboyd@...omium.org>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        intel-gfx@...ts.freedesktop.org, linux-arm-msm@...r.kernel.org,
        freedreno@...ts.freedesktop.org, linux-usb@...r.kernel.org
Subject: Re: [PATCH 2/2] drm/msm/dp: Implement oob_hotplug_event()

On Mon, Feb 07, 2022 at 08:43:28PM -0800, Bjorn Andersson wrote:
> The Qualcomm DisplayPort driver contains traces of the necessary
> plumbing to hook up USB HPD, in the form of the dp_hpd module and the
> dp_usbpd_cb struct. Use this as basis for implementing the
> oob_hotplug_event() callback, by amending the dp_hpd module with the
> missing logic.
> 
> Overall the solution is similar to what's done downstream, but upstream
> all the code to disect the HPD notification lives on the calling side of
> drm_connector_oob_hotplug_event().
> 
> drm_connector_oob_hotplug_event() performs the lookup of the
> drm_connector based on fwnode, hence the need to assign the fwnode in
> dp_drm_connector_init().
> 
> Signed-off-by: Bjorn Andersson <bjorn.andersson@...aro.org>
> ---
>  drivers/gpu/drm/msm/dp/dp_display.c |  8 ++++++++
>  drivers/gpu/drm/msm/dp/dp_display.h |  2 ++
>  drivers/gpu/drm/msm/dp/dp_drm.c     | 10 ++++++++++
>  drivers/gpu/drm/msm/dp/dp_hpd.c     | 19 +++++++++++++++++++
>  drivers/gpu/drm/msm/dp/dp_hpd.h     |  4 ++++
>  5 files changed, 43 insertions(+)
> 
> diff --git a/drivers/gpu/drm/msm/dp/dp_display.c b/drivers/gpu/drm/msm/dp/dp_display.c
> index 7cc4d21f2091..124a2f794382 100644
> --- a/drivers/gpu/drm/msm/dp/dp_display.c
> +++ b/drivers/gpu/drm/msm/dp/dp_display.c
> @@ -414,6 +414,13 @@ static int dp_display_usbpd_configure_cb(struct device *dev)
>  	return dp_display_process_hpd_high(dp);
>  }
>  
> +void dp_display_oob_hotplug_event(struct msm_dp *dp_display, bool hpd_state)
> +{
> +	struct dp_display_private *dp = container_of(dp_display, struct dp_display_private, dp_display);
> +
> +	dp->usbpd->oob_event(dp->usbpd, hpd_state);
> +}
> +
>  static int dp_display_usbpd_disconnect_cb(struct device *dev)
>  {
>  	struct dp_display_private *dp = dev_get_dp_display_private(dev);
> @@ -1251,6 +1258,7 @@ static int dp_display_probe(struct platform_device *pdev)
>  	dp->pdev = pdev;
>  	dp->name = "drm_dp";
>  	dp->dp_display.connector_type = desc->connector_type;
> +	dp->dp_display.dev = &pdev->dev;

You did not properly reference count this pointer you just saved.  What
is to keep that pointer from going away without you knowing about it?

And you already have a pointer to pdev, why save another one here?

>  
>  	rc = dp_init_sub_modules(dp);
>  	if (rc) {
> diff --git a/drivers/gpu/drm/msm/dp/dp_display.h b/drivers/gpu/drm/msm/dp/dp_display.h
> index e3adcd578a90..1f856b3bca79 100644
> --- a/drivers/gpu/drm/msm/dp/dp_display.h
> +++ b/drivers/gpu/drm/msm/dp/dp_display.h
> @@ -11,6 +11,7 @@
>  #include "disp/msm_disp_snapshot.h"
>  
>  struct msm_dp {
> +	struct device *dev;
>  	struct drm_device *drm_dev;
>  	struct device *codec_dev;

So you now have pointers to 3 different devices here?  What does 'dev'
point to that the other ones do not?  This needs to be documented really
well here.

thanks,

greg k-h