linux-kernel - Re: [PATCH 1/3] drm/draw: add drm_draw_can_convert_from

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Message-ID: <2764907.vuYhMxLoTh@fedora.fritz.box>
Date: Mon, 06 Oct 2025 23:38:53 +0200
From: Francesco Valla <francesco@...la.it>
To: Jocelyn Falempe <jfalempe@...hat.com>,
 Javier Martinez Canillas <javierm@...hat.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>,
 Jani Nikula <jani.nikula@...ux.intel.com>
Cc: dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] drm/draw: add drm_draw_can_convert_from_xrgb8888

On Monday, 6 October 2025 at 08:48:51 Jani Nikula <jani.nikula@...ux.intel.com> wrote:
> On Sun, 05 Oct 2025, Francesco Valla <francesco@...la.it> wrote:
> > Add drm_draw_can_convert_from_xrgb8888() function that can be used to
> > determine if a XRGB8888 color can be converted to the specified format.
> >
> > Signed-off-by: Francesco Valla <francesco@...la.it>
> > ---
> >  drivers/gpu/drm/drm_draw.c          | 84 +++++++++++++++++++++++++++----------
> >  drivers/gpu/drm/drm_draw_internal.h |  2 +
> >  2 files changed, 63 insertions(+), 23 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/drm_draw.c b/drivers/gpu/drm/drm_draw.c
> > index 9dc0408fbbeadbe8282a2d6b210e0bfb0672967f..2641026a103d3b28cab9f5d378604b0604520fe4 100644
> > --- a/drivers/gpu/drm/drm_draw.c
> > +++ b/drivers/gpu/drm/drm_draw.c
> > @@ -15,45 +15,83 @@
> >  #include "drm_draw_internal.h"
> >  #include "drm_format_internal.h"
> >  
> > -/**
> > - * drm_draw_color_from_xrgb8888 - convert one pixel from xrgb8888 to the desired format
> > - * @color: input color, in xrgb8888 format
> > - * @format: output format
> > - *
> > - * Returns:
> > - * Color in the format specified, casted to u32.
> > - * Or 0 if the format is not supported.
> > - */
> > -u32 drm_draw_color_from_xrgb8888(u32 color, u32 format)
> > +static int __drm_draw_color_from_xrgb8888(u32 color, u32 format, u32 *out_color)
> 
> Is there any reason to change the return value of this function and
> return the result via out_color? It already returns 0 if the format is
> not supported. If there's a reason, it needs to be in the commit
> message.
> 

Is because 0 might be a valid color (e.g black for RGB888), as Jocelyn
correctly pointed out in another thread. I'll add this detail to the
commit message for the V2.

> >  {
> >  	switch (format) {
> >  	case DRM_FORMAT_RGB565:
> > -		return drm_pixel_xrgb8888_to_rgb565(color);
> > +		*out_color = drm_pixel_xrgb8888_to_rgb565(color);
> > +		break;
> >  	case DRM_FORMAT_RGBA5551:
> > -		return drm_pixel_xrgb8888_to_rgba5551(color);
> > +		*out_color = drm_pixel_xrgb8888_to_rgba5551(color);
> > +		break;
> >  	case DRM_FORMAT_XRGB1555:
> > -		return drm_pixel_xrgb8888_to_xrgb1555(color);
> > +		*out_color = drm_pixel_xrgb8888_to_xrgb1555(color);
> > +		break;
> >  	case DRM_FORMAT_ARGB1555:
> > -		return drm_pixel_xrgb8888_to_argb1555(color);
> > +		*out_color = drm_pixel_xrgb8888_to_argb1555(color);
> > +		break;
> >  	case DRM_FORMAT_RGB888:
> > +		fallthrough;
> 
> That's not necessary for back to back case labels. Please don't add it.
>

Noted.

> >  	case DRM_FORMAT_XRGB8888:
> > -		return color;
> > +		*out_color = color;
> > +		break;
> >  	case DRM_FORMAT_ARGB8888:
> > -		return drm_pixel_xrgb8888_to_argb8888(color);
> > +		*out_color = drm_pixel_xrgb8888_to_argb8888(color);
> > +		break;
> >  	case DRM_FORMAT_XBGR8888:
> > -		return drm_pixel_xrgb8888_to_xbgr8888(color);
> > +		*out_color = drm_pixel_xrgb8888_to_xbgr8888(color);
> > +		break;
> >  	case DRM_FORMAT_ABGR8888:
> > -		return drm_pixel_xrgb8888_to_abgr8888(color);
> > +		*out_color = drm_pixel_xrgb8888_to_abgr8888(color);
> > +		break;
> >  	case DRM_FORMAT_XRGB2101010:
> > -		return drm_pixel_xrgb8888_to_xrgb2101010(color);
> > +		*out_color = drm_pixel_xrgb8888_to_xrgb2101010(color);
> > +		break;
> >  	case DRM_FORMAT_ARGB2101010:
> > -		return drm_pixel_xrgb8888_to_argb2101010(color);
> > +		*out_color = drm_pixel_xrgb8888_to_argb2101010(color);
> > +		break;
> >  	case DRM_FORMAT_ABGR2101010:
> > -		return drm_pixel_xrgb8888_to_abgr2101010(color);
> > +		*out_color = drm_pixel_xrgb8888_to_abgr2101010(color);
> > +		break;
> >  	default:
> > -		WARN_ONCE(1, "Can't convert to %p4cc\n", &format);
> > -		return 0;
> > +		return -1;
> 
> Please don't use -1 as a generic error code. -1 is -EPERM.
> 

Whops, you're right. I'll return -ENOTSUPP.

> >  	}
> > +
> > +	return 0;
> > +}
> > +
> > +/**
> > + * drm_draw_can_convert_from_xrgb8888 - check if xrgb8888 can be converted to the desired format
> > + * @format: format
> > + *
> > + * Returns:
> > + * True if XRGB8888 can be converted to the specified format, false otherwise.
> > + */
> > +bool drm_draw_can_convert_from_xrgb8888(u32 format)
> > +{
> > +	u32 out_color;
> > +
> > +	return __drm_draw_color_from_xrgb8888(0, format, &out_color) == 0;
> > +}
> > +EXPORT_SYMBOL(drm_draw_can_convert_from_xrgb8888);
> > +
> > +/**
> > + * drm_draw_color_from_xrgb8888 - convert one pixel from xrgb8888 to the desired format
> > + * @color: input color, in xrgb8888 format
> > + * @format: output format
> > + *
> > + * Returns:
> > + * Color in the format specified, casted to u32.
> > + * Or 0 if the format is not supported.
> > + */
> > +u32 drm_draw_color_from_xrgb8888(u32 color, u32 format)
> > +{
> > +	u32 out_color = 0;
> > +
> > +	if (__drm_draw_color_from_xrgb8888(color, format, &out_color))
> > +		WARN_ONCE(1, "Can't convert to %p4cc\n", &format);
> > +
> > +	return out_color;
> >  }
> >  EXPORT_SYMBOL(drm_draw_color_from_xrgb8888);
> >  
> > diff --git a/drivers/gpu/drm/drm_draw_internal.h b/drivers/gpu/drm/drm_draw_internal.h
> > index f121ee7339dc11537f677c833f0ee94fe0e799cd..2ab4cb341df94fc4173dd6f5e7a512bdcfa5e55c 100644
> > --- a/drivers/gpu/drm/drm_draw_internal.h
> > +++ b/drivers/gpu/drm/drm_draw_internal.h
> > @@ -24,6 +24,8 @@ static inline const u8 *drm_draw_get_char_bitmap(const struct font_desc *font,
> >  	return font->data + (c * font->height) * font_pitch;
> >  }
> >  
> > +bool drm_draw_can_convert_from_xrgb8888(u32 format);
> > +
> >  u32 drm_draw_color_from_xrgb8888(u32 color, u32 format);
> >  
> >  void drm_draw_blit16(struct iosys_map *dmap, unsigned int dpitch,
> 
> 

Thank you.

Best regards,

--

Francesco