linux-kernel - Re: [PATCH] drm: bridge: adv7511: get edid in hpd

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Message-ID: <20231016081749.GE23177@pendragon.ideasonboard.com>
Date:   Mon, 16 Oct 2023 11:17:49 +0300
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Alvin Šipraga <alvin@...s.dk>
Cc:     Andrzej Hajda <andrzej.hajda@...el.com>,
        Neil Armstrong <neil.armstrong@...aro.org>,
        Robert Foss <rfoss@...nel.org>,
        Jonas Karlman <jonas@...boo.se>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Alvin Šipraga <alsi@...g-olufsen.dk>,
        Hans Verkuil <hverkuil-cisco@...all.nl>
Subject: Re: [PATCH] drm: bridge: adv7511: get edid in hpd_work to update CEC
 phys address

Hi Alvin,

Thank you for the patch.

CC'ing Hans Verkuil, to review the CEC side.

On Sat, Oct 14, 2023 at 09:43:01PM +0200, Alvin Šipraga wrote:
> From: Alvin Šipraga <alsi@...g-olufsen.dk>
> 
> The adv7511 driver is solely responsible for setting the physical
> address of its CEC adapter. To do this, it must read the EDID. However,
> EDID is only read when either the drm_bridge_funcs :: get_edid or
> drm_connector_helper_funcs :: get_modes ops are called. Without loss of
> generality, it cannot be assumed that these ops are called when a sink
> gets attached. Therefore there exist scenarios in which the CEC physical
> address will be invalid (f.f.f.f), rendering the CEC adapter inoperable.
> 
> Address this problem by always fetching the EDID in the HPD work when we
> detect a connection. The CEC physical address is set in the process.
> 
> Signed-off-by: Alvin Šipraga <alsi@...g-olufsen.dk>
> ---
> Pardon the insertion of the ugly adv7511_get_edid() prototype, but I did
> not want to clobber git history by rearranging a bunch of functions. If
> this is the preferred approach I will happily re-spin the patch.

There's nothing wrong in rearranging functions, it is actually preferred
to adding forward declarations. You can submit a set of two patches, one
to reorder the functions, and then a second one to fix the problem. This
makes review easier by isolating the refactoring with no functional
change from the functional changes.

> ---
>  drivers/gpu/drm/bridge/adv7511/adv7511_drv.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c b/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c
> index 2611afd2c1c1..3d32c109963c 100644
> --- a/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c
> +++ b/drivers/gpu/drm/bridge/adv7511/adv7511_drv.c
> @@ -424,6 +424,9 @@ static bool adv7511_hpd(struct adv7511 *adv7511)
>  	return false;
>  }
>  
> +static struct edid *adv7511_get_edid(struct adv7511 *adv7511,
> +				     struct drm_connector *connector);
> +
>  static void adv7511_hpd_work(struct work_struct *work)
>  {
>  	struct adv7511 *adv7511 = container_of(work, struct adv7511, hpd_work);
> @@ -457,6 +460,9 @@ static void adv7511_hpd_work(struct work_struct *work)
>  		if (adv7511->connector.dev) {
>  			if (status == connector_status_disconnected)
>  				cec_phys_addr_invalidate(adv7511->cec_adap);
> +			else
> +				adv7511_get_edid(adv7511, &adv7511->connector);
> +
>  			drm_kms_helper_hotplug_event(adv7511->connector.dev);
>  		} else {
>  			drm_bridge_hpd_notify(&adv7511->bridge, status);
> 

-- 
Regards,

Laurent Pinchart