linux-kernel - Re: [PATCH v2] drm/gma500: replace drm_detect_hdmi_monitor() with drm_display_info.is

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Message-ID: <87ldzxi71s.fsf@intel.com>
Date: Thu, 12 Sep 2024 11:56:47 +0300
From: Jani Nikula <jani.nikula@...ux.intel.com>
To: Thomas Zimmermann <tzimmermann@...e.de>, Tejas Vipin
 <tejasvipin76@...il.com>, Laurent.pinchart@...asonboard.com,
 patrik.r.jakobsson@...il.com, maarten.lankhorst@...ux.intel.com,
 mripard@...nel.org, airlied@...il.com, daniel@...ll.ch
Cc: dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] drm/gma500: replace drm_detect_hdmi_monitor() with
 drm_display_info.is_hdmi

On Thu, 12 Sep 2024, Jani Nikula <jani.nikula@...ux.intel.com> wrote:
> On Thu, 12 Sep 2024, Thomas Zimmermann <tzimmermann@...e.de> wrote:
>> Hi
>>
>> Am 11.09.24 um 20:06 schrieb Tejas Vipin:
>>> Replace drm_detect_hdmi_monitor() with drm_display_info.is_hdmi since
>>> monitor HDMI information is available after EDID is parsed. Additionally
>>> rewrite the code the code to have fewer indentation levels.
>>
>> The problem is that the entire logic is outdated. The content 
>> of cdv_hdmi_detect() should go into cdv_hdmi_get_modes(), the detect_ctx 
>> callback should be set to drm_connector_helper_detect_from_ddc() and 
>> cdv_hdmi_detect() should be deleted. The result is that ->detect_ctx 
>> will detect the presence of a display and ->get_modes will update EDID 
>> and other properties.
>
> I guess I didn't get the memo on this one.
>
> What's the problem with reading the EDID at detect? The subsequent
> drm_edid_connector_add_modes() called from .get_modes() does not need to
> read the EDID again.

Moreover, in this case .detect() only detects digital displays as
reported by EDID. If you postpone that to .get_modes(), the probe helper
will still report connected, and invent non-EDID fallback modes. The
behaviour changes.

> I think it should be fine to do incremental refactors like the patch at
> hand (modulo some issues I mention below).

Another issue in the patch is that it should also change .get_modes() to
not read the EDID again, but just call drm_edid_connector_add_modes().

BR,
Jani.

>
> BR,
> Jani.
>
>
>>
>> Do you have  a device for testing such a change?
>>
>> Best regards
>> Thomas
>>
>>>
>>> Signed-off-by: Tejas Vipin <tejasvipin76@...il.com>
>>> ---
>>> Changes in v2:
>>>      - Use drm_edid instead of edid
>>>
>>> Link to v1: https://lore.kernel.org/all/20240910051856.700210-1-tejasvipin76@gmail.com/
>>> ---
>>>   drivers/gpu/drm/gma500/cdv_intel_hdmi.c | 24 +++++++++++++-----------
>>>   1 file changed, 13 insertions(+), 11 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/gma500/cdv_intel_hdmi.c b/drivers/gpu/drm/gma500/cdv_intel_hdmi.c
>>> index 2d95e0471291..701f8bbd5f2b 100644
>>> --- a/drivers/gpu/drm/gma500/cdv_intel_hdmi.c
>>> +++ b/drivers/gpu/drm/gma500/cdv_intel_hdmi.c
>>> @@ -128,23 +128,25 @@ static enum drm_connector_status cdv_hdmi_detect(
>>>   {
>>>   	struct gma_encoder *gma_encoder = gma_attached_encoder(connector);
>>>   	struct mid_intel_hdmi_priv *hdmi_priv = gma_encoder->dev_priv;
>>> -	struct edid *edid = NULL;
>>> +	const struct drm_edid *drm_edid;
>>> +	int ret;
>>>   	enum drm_connector_status status = connector_status_disconnected;
>>>   
>>> -	edid = drm_get_edid(connector, connector->ddc);
>>> +	drm_edid = drm_edid_read_ddc(connector, connector->ddc);
>
> Just drm_edid_read() is enough when you're using connector->ddc.
>
>>> +	ret = drm_edid_connector_update(connector, drm_edid);
>>>   
>>>   	hdmi_priv->has_hdmi_sink = false;
>>>   	hdmi_priv->has_hdmi_audio = false;
>>> -	if (edid) {
>>> -		if (edid->input & DRM_EDID_INPUT_DIGITAL) {
>>> -			status = connector_status_connected;
>>> -			hdmi_priv->has_hdmi_sink =
>>> -						drm_detect_hdmi_monitor(edid);
>>> -			hdmi_priv->has_hdmi_audio =
>>> -						drm_detect_monitor_audio(edid);
>>> -		}
>>> -		kfree(edid);
>>> +	if (ret)
>
> This error path leaks the EDID.
>
>>> +		return status;
>>> +
>>> +	if (drm_edid_is_digital(drm_edid)) {
>>> +		status = connector_status_connected;
>>> +		hdmi_priv->has_hdmi_sink = connector->display_info.is_hdmi;
>>> +		hdmi_priv->has_hdmi_audio = connector->display_info.has_audio;
>>>   	}
>>> +	drm_edid_free(drm_edid);
>>> +
>>>   	return status;
>>>   }
>>>   

-- 
Jani Nikula, Intel