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

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Message-ID: <42b27020-a68e-4c43-800e-61977324be78@suse.de>
Date: Thu, 12 Sep 2024 11:18:45 +0200
From: Thomas Zimmermann <tzimmermann@...e.de>
To: Jani Nikula <jani.nikula@...ux.intel.com>,
 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

Hi

Am 12.09.24 um 10:48 schrieb Jani Nikula:
> 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 The problem is that the entire logic is outdated.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.

With drm_connector_helper_detect_from_ddc() there is already a helper 
for detection. It makes sense to use it. And if we continue to update 
the properties in detect (instead of get_modes), what is the correct 
connector_status on errors? Right now and with the patch applied, detect 
returns status_disconnected on errors. But this isn't correct if there 
actually is a display. By separating detect and get_modes cleanly, we 
can detect the display reliably, but also handle errors better than we 
currently do in gma500. Get_modes is already expected to update the EDID 
property, [1] for detect it's not so clear AFAICT. I think that from a 
design perspective, it makes sense to have a read-only function that 
only detects the physical state of the connector and a read-write 
function that updates the connector's properties. Best regards Thomas 
[1] 
https://elixir.bootlin.com/linux/v6.10.9/source/include/drm/drm_modeset_helper_vtables.h#L865 

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

-- 
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)