linux-kernel - Re: [PATCH v4 4/8] drm/vkms: Add support for RGB565 formats

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Message-ID: <e6c6b09d-7b52-4e89-9fd5-1f60916dd3cf@bootlin.com>
Date: Fri, 13 Jun 2025 19:38:54 +0200
From: Louis Chauvet <louis.chauvet@...tlin.com>
To: Maíra Canal <mcanal@...lia.com>,
 Melissa Wen <melissa.srw@...il.com>, Maíra Canal
 <mairacanal@...eup.net>, Haneen Mohammed <hamohammed.sa@...il.com>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>,
 David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
 Rodrigo Siqueira <siqueira@...lia.com>,
 Simona Vetter <simona.vetter@...ll.ch>
Cc: dri-devel@...ts.freedesktop.org, arthurgrillo@...eup.net,
 linux-kernel@...r.kernel.org, jeremie.dautheribes@...tlin.com,
 miquel.raynal@...tlin.com, thomas.petazzoni@...tlin.com,
 seanpaul@...gle.com, nicolejadeyee@...gle.com
Subject: Re: [PATCH v4 4/8] drm/vkms: Add support for RGB565 formats



Le 11/06/2025 à 22:02, Maíra Canal a écrit :
> Hi Louis,
> 
> On 5/30/25 11:05, Louis Chauvet wrote:
>> The format RGB565 was already supported. Add the support for:
>> - BGR565
>>
>> Signed-off-by: Louis Chauvet <louis.chauvet@...tlin.com>
>> ---
>>    drivers/gpu/drm/vkms/vkms_formats.c | 23 +++++++++++++++++++++++
>>    drivers/gpu/drm/vkms/vkms_plane.c   |  1 +
>>    2 files changed, 24 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/vkms/vkms_formats.c b/drivers/gpu/drm/vkms/vkms_formats.c
>> index 95771bff5202..2c5cc8d3a14c 100644
>> --- a/drivers/gpu/drm/vkms/vkms_formats.c
>> +++ b/drivers/gpu/drm/vkms/vkms_formats.c
>> @@ -259,6 +259,26 @@ static struct pixel_argb_u16 argb_u16_from_grayu16(u16 gray)
>>    	return argb_u16_from_u16161616(0xFFFF, gray, gray, gray);
>>    }
>>    
>> +static struct pixel_argb_u16 argb_u16_from_BGR565(const __le16 *pixel)
>> +{
>> +	struct pixel_argb_u16 out_pixel;
>> +
>> +	s64 fp_rb_ratio = drm_fixp_div(drm_int2fixp(65535), drm_int2fixp(31));
>> +	s64 fp_g_ratio = drm_fixp_div(drm_int2fixp(65535), drm_int2fixp(63));
>> +
>> +	u16 rgb_565 = le16_to_cpu(*pixel);
>> +	s64 fp_b = drm_int2fixp((rgb_565 >> 11) & 0x1f);
>> +	s64 fp_g = drm_int2fixp((rgb_565 >> 5) & 0x3f);
>> +	s64 fp_r = drm_int2fixp(rgb_565 & 0x1f);
>> +
>> +	out_pixel.a = (u16)0xffff;
>> +	out_pixel.b = drm_fixp2int_round(drm_fixp_mul(fp_b, fp_rb_ratio));
>> +	out_pixel.g = drm_fixp2int_round(drm_fixp_mul(fp_g, fp_g_ratio));
>> +	out_pixel.r = drm_fixp2int_round(drm_fixp_mul(fp_r, fp_rb_ratio));
>> +
>> +	return out_pixel;
>> +}
> 
> Instead of writing `argb_u16_from_BGR565()` from scratch, I wonder if
> we could just call `argb_u16_from_RGB565()` and swap `out_pixel.b` with
> `out_pixel.r` . For me, it looks like a cleaner approach.

Thanks for the suggestion, I was looking to avoid code repetition, but I 
did not think about this kind of "post-processing".

I will do for the next revision.

> Well, even without this suggestion,
> 
> Reviewed-by: Maíra Canal <mcanal@...lia.com>
> 
> Best Regards,
> - Maíra
> 
>> +
>>    VISIBLE_IF_KUNIT struct pixel_argb_u16 argb_u16_from_yuv888(u8 y, u8 channel_1, u8 channel_2,
>>    							    const struct conversion_matrix *matrix)
>>    {
>> @@ -447,6 +467,7 @@ READ_LINE_le16161616(XRGB16161616_read_line, px, cpu_to_le16(0xFFFF), px[2], px[
>>    READ_LINE_le16161616(XBGR16161616_read_line, px, cpu_to_le16(0xFFFF), px[0], px[1], px[2])
>>    
>>    READ_LINE(RGB565_read_line, px, __le16, argb_u16_from_RGB565, px)
>> +READ_LINE(BGR565_read_line, px, __le16, argb_u16_from_BGR565, px)
>>    
>>    READ_LINE(R8_read_line, px, u8, argb_u16_from_gray8, *px)
>>    
>> @@ -675,6 +696,8 @@ pixel_read_line_t get_pixel_read_line_function(u32 format)
>>    		return &XBGR16161616_read_line;
>>    	case DRM_FORMAT_RGB565:
>>    		return &RGB565_read_line;
>> +	case DRM_FORMAT_BGR565:
>> +		return &BGR565_read_line;
>>    	case DRM_FORMAT_NV12:
>>    	case DRM_FORMAT_NV16:
>>    	case DRM_FORMAT_NV24:
>> diff --git a/drivers/gpu/drm/vkms/vkms_plane.c b/drivers/gpu/drm/vkms/vkms_plane.c
>> index 505847ec8508..d3783a8f84c2 100644
>> --- a/drivers/gpu/drm/vkms/vkms_plane.c
>> +++ b/drivers/gpu/drm/vkms/vkms_plane.c
>> @@ -26,6 +26,7 @@ static const u32 vkms_formats[] = {
>>    	DRM_FORMAT_ARGB16161616,
>>    	DRM_FORMAT_ABGR16161616,
>>    	DRM_FORMAT_RGB565,
>> +	DRM_FORMAT_BGR565,
>>    	DRM_FORMAT_NV12,
>>    	DRM_FORMAT_NV16,
>>    	DRM_FORMAT_NV24,
>>
> 

-- 
Louis Chauvet, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com