Re: [PATCH v6 09/10] drm/vc4: hdmi: stop rereading EDID in get_modes()

[Maxime Ripard <mripard@xxxxxxxxxx>]

Hi,

On Fri, Dec 06, 2024 at 12:16:03PM +0200, Dmitry Baryshkov wrote:
> The vc4_hdmi_connector_detect_ctx() via vc4_hdmi_handle_hotplug()
> already reads EDID and propagates it to the drm_connector. Stop
> rereading EDID as a part of the .get_modes() callback and just update
> the list of modes. This matches the behaviour of the i915 driver.
> 
> Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxx>
> ---
>  drivers/gpu/drm/vc4/vc4_hdmi.c | 21 ---------------------
>  1 file changed, 21 deletions(-)
> 
> diff --git a/drivers/gpu/drm/vc4/vc4_hdmi.c b/drivers/gpu/drm/vc4/vc4_hdmi.c
> index e5ab42f72f618b90f956482db6c9c8074c1e3bf1..3364ef90968dad3074800f02926300ffceb75c69 100644
> --- a/drivers/gpu/drm/vc4/vc4_hdmi.c
> +++ b/drivers/gpu/drm/vc4/vc4_hdmi.c
> @@ -470,31 +470,10 @@ static int vc4_hdmi_connector_detect_ctx(struct drm_connector *connector,
>  
>  static int vc4_hdmi_connector_get_modes(struct drm_connector *connector)
>  {
> -	struct vc4_hdmi *vc4_hdmi = connector_to_vc4_hdmi(connector);
>  	struct vc4_dev *vc4 = to_vc4_dev(connector->dev);
> -	const struct drm_edid *drm_edid;
>  	int ret = 0;
>  
> -	/*
> -	 * NOTE: This function should really take vc4_hdmi->mutex, but doing so
> -	 * results in reentrancy issues since cec_s_phys_addr() might call
> -	 * .adap_enable, which leads to that funtion being called with our mutex
> -	 * held.
> -	 *
> -	 * Concurrency isn't an issue at the moment since we don't share
> -	 * any state with any of the other frameworks so we can ignore
> -	 * the lock for now.
> -	 */
> -
> -	drm_edid = drm_edid_read_ddc(connector, vc4_hdmi->ddc);
> -	drm_edid_connector_update(connector, drm_edid);
> -	cec_s_phys_addr(vc4_hdmi->cec_adap,
> -			connector->display_info.source_physical_address, false);
> -	if (!drm_edid)
> -		return 0;
> -
>  	ret = drm_edid_connector_add_modes(connector);
> -	drm_edid_free(drm_edid);

I don't think that works though, for mostly two reasons:

 1) We're not sure we'll even have an hotplug interrupt if the system
    boots with the connector plugged in for example.

 2) afaik, the get_modes ioctl directly calls get_modes too.

Maxime

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