linux-kernel - Re: [PATCH RESEND v2 15/32] drm/vkms: Introduce configfs for plane color range

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Message-ID: <5eeedbf9-7ca0-4e5b-9db0-616866af4ac8@bootlin.com>
Date: Fri, 19 Dec 2025 17:55:19 +0100
From: Louis Chauvet <louis.chauvet@...tlin.com>
To: Luca Ceresoli <luca.ceresoli@...tlin.com>,
 Haneen Mohammed <hamohammed.sa@...il.com>, Simona Vetter <simona@...ll.ch>,
 Melissa Wen <melissa.srw@...il.com>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>,
 David Airlie <airlied@...il.com>, jose.exposito89@...il.com,
 Jonathan Corbet <corbet@....net>
Cc: victoria@...tem76.com, sebastian.wick@...hat.com,
 thomas.petazzoni@...tlin.com, dri-devel@...ts.freedesktop.org,
 linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org
Subject: Re: [PATCH RESEND v2 15/32] drm/vkms: Introduce configfs for plane
 color range



On 12/18/25 19:00, Luca Ceresoli wrote:
> On Wed Oct 29, 2025 at 3:36 PM CET, Louis Chauvet wrote:
>> To allows the userspace to test many hardware configuration, introduce a
>> new interface to configure the available color ranges per planes. VKMS
>> supports multiple color ranges, so the userspace can choose any
>> combination.
>>
>> The supported color ranges are configured by writing a color range bitmask
>> to the file `supported_color_ranges` and the default color range is
>> chosen by writing a color encoding bitmask to `default_color_range`.
>>
>> Signed-off-by: Louis Chauvet <louis.chauvet@...tlin.com>
> 
>> diff --git a/drivers/gpu/drm/vkms/vkms_configfs.c b/drivers/gpu/drm/vkms/vkms_configfs.c
>> index ee2e8d141f9e..3f658dd41272 100644
>> --- a/drivers/gpu/drm/vkms/vkms_configfs.c
>> +++ b/drivers/gpu/drm/vkms/vkms_configfs.c
>> @@ -439,6 +439,91 @@ static ssize_t plane_default_rotation_store(struct config_item *item,
>>   	return count;
>>   }
>>
>> +static ssize_t plane_supported_color_ranges_show(struct config_item *item, char *page)
>> +{
>> +	struct vkms_configfs_plane *plane;
>> +	unsigned int supported_color_range;
>                       supported_color_ranges
> 
>> +
>> +	plane = plane_item_to_vkms_configfs_plane(item);
> 
> As for previous patches, set this on declaration for consistency (same below).
> 
>> +static ssize_t plane_supported_color_ranges_store(struct config_item *item,
>> +						  const char *page, size_t count)
>> +{
>> +	struct vkms_configfs_plane *plane = plane_item_to_vkms_configfs_plane(item);
>> +	int ret, val = 0;
>> +
>> +	ret = kstrtouint(page, 10, &val);
>> +	if (ret)
>> +		return ret;
>> +
>> +	/* Should be a supported value */
>> +	if (val & ~(BIT(DRM_COLOR_YCBCR_LIMITED_RANGE) |
>> +		    BIT(DRM_COLOR_YCBCR_FULL_RANGE)))
>> +		return -EINVAL;
>> +	/* Should at least provide one color range */
>> +	if ((val & (BIT(DRM_COLOR_YCBCR_LIMITED_RANGE) |
>> +		    BIT(DRM_COLOR_YCBCR_FULL_RANGE))) == 0)
>> +		return -EINVAL;
>> +
>> +	scoped_guard(mutex, &plane->dev->lock) {
>> +		/* Ensures that the default rotation is included in supported rotation */
> 
> Oh no, that comment again! :-)
> 
>> +static ssize_t plane_default_color_range_store(struct config_item *item,
>> +					       const char *page, size_t count)
>> +{
>> +	struct vkms_configfs_plane *plane = plane_item_to_vkms_configfs_plane(item);
>> +	int ret, val = 0;
>> +
>> +	ret = kstrtouint(page, 10, &val);
>> +	if (ret)
>> +		return ret;
>> +
>> +	/* Should be a supported value */
>> +	if (val & ~(BIT(DRM_COLOR_YCBCR_LIMITED_RANGE) |
>> +		    BIT(DRM_COLOR_YCBCR_FULL_RANGE)))
>> +		return -EINVAL;
>> +	/* Should at least provide one color range */
>> +	if ((val & (BIT(DRM_COLOR_YCBCR_LIMITED_RANGE) |
>> +		    BIT(DRM_COLOR_YCBCR_FULL_RANGE))) == 0)
>> +		return -EINVAL;
> 
> As in patch 12, replace this with is_power_of_2() to check that exactly one
> bit is set.

And as the previous patch, this code is simply wrong...
I shoud check if val is one of DRM_COLOR_YCBCR_LIMITED_RANGE / 
DRM_COLOR_YCBCR_FULL_RANGE

Thanks

> Luca
> 
> --
> Luca Ceresoli, Bootlin
> Embedded Linux and Kernel engineering
> https://bootlin.com