linux-kernel - Re: [PATCH v4 06/23] drm/connector: hdmi: Use YUV420 output format as an RGB fallback

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Message-ID: <7729efd6-fa88-4022-b8d8-b32fe49bf4aa@collabora.com>
Date: Thu, 15 May 2025 15:44:18 +0300
From: Cristian Ciocaltea <cristian.ciocaltea@...labora.com>
To: Maxime Ripard <mripard@...nel.org>
Cc: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Thomas Zimmermann <tzimmermann@...e.de>, David Airlie <airlied@...il.com>,
 Simona Vetter <simona@...ll.ch>,
 Dave Stevenson <dave.stevenson@...pberrypi.com>,
 Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>,
 Dmitry Baryshkov <lumag@...nel.org>, kernel@...labora.com,
 dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 06/23] drm/connector: hdmi: Use YUV420 output format as
 an RGB fallback

Hi Maxime,

On 5/13/25 4:35 PM, Maxime Ripard wrote:
> Hi,
> 
> On Fri, Apr 25, 2025 at 01:26:57PM +0300, Cristian Ciocaltea wrote:
>> Try to make use of YUV420 when computing the best output format and
>> RGB cannot be supported for any of the available color depths.
>>
>> Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@...labora.com>
>> ---
>>  drivers/gpu/drm/display/drm_hdmi_state_helper.c | 22 +++++++++++++++++-----
>>  1 file changed, 17 insertions(+), 5 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/display/drm_hdmi_state_helper.c b/drivers/gpu/drm/display/drm_hdmi_state_helper.c
>> index 9e0a468073acbb2477eff1abef1c09d63620afaa..1fba10b92a6baa49150b6ff1e96bf2c2739bf269 100644
>> --- a/drivers/gpu/drm/display/drm_hdmi_state_helper.c
>> +++ b/drivers/gpu/drm/display/drm_hdmi_state_helper.c
>> @@ -648,14 +648,26 @@ hdmi_compute_config(const struct drm_connector *connector,
>>  				       8, connector->max_bpc);
>>  	int ret;
>>  
>> -	/*
>> -	 * TODO: Add support for YCbCr420 output for HDMI 2.0 capable
>> -	 * devices, for modes that only support YCbCr420.
>> -	 */
>>  	ret = hdmi_compute_format_bpc(connector, conn_state, mode, max_bpc,
>>  				      HDMI_COLORSPACE_RGB);
>> +	if (!ret)
>> +		return 0;
> 
> Sorry, I missed it on the previous iteration, but this condition
> inversion compared to the rest of the function is throwing me off :)
> 
> I believe something like
> 
> If (ret) {
>    if (connector->ycbcr_420_allowed) {
>       hdmi_compute_format_bpc(..., HDMI_COLORSPACE_YUV420)
>    } else {
>      drm_dbg_kms("Can't use YUV420")
>    }
> }
> 
> Would be more natural

Yep, will do.

Please let me know if I can start preparing v5, as I'm not sure if you
managed to also check the test-related patches.

Thanks,
Cristian