linux-kernel - [PATCH v2 0/3] drm/draw: add check API to avoid spurious WARN

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Message-Id: <20251014-drm_draw_conv_check-v2-0-05bef3eb06fb@valla.it>
Date: Tue, 14 Oct 2025 22:08:11 +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>
Cc: dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org, 
 Francesco Valla <francesco@...la.it>
Subject: [PATCH v2 0/3] drm/draw: add check API to avoid spurious WARN

When using the DRM draw support, the only way to check if a color can be
converted from XRGB8888 to a target format is currently to attempt an
actual conversion using drm_draw_color_from_xrgb8888(). This function
however will print a WARN the first time a conversion cannot be
performed, leading to two potential issues:

 - a WARN is emitted without a real reason if the caller is only
   attempting a conversion to check if a format can be supported (which
   is the case for two of the current user of this API);
 - a failing call following the first one is not emitting a WARN, but a
   "valid" color value (0x00000000) is returned nevertheless.

The first issue was observed while using drm_log on a Beagleplay, which
lists AR12 as the first format for its HDMI modesets.

The target of this patch set is to improve this situation; the first
patch introduces a new API devoted only to check if a conversion from
XRGB8888 to the specified format can be performed, while the other two
substitute drm_draw_color_from_xrgb8888() with this new API in the
current users (drm_panic and drm_log) where relevant.

Signed-off-by: Francesco Valla <francesco@...la.it>
---
Changes in v2:
- Moved to dedicated switch cases in separate functions instead of
  single one inside common function.
- Fix copy-paste error in commit message.

Link to v1: https://lore.kernel.org/r/20251005-drm_draw_conv_check-v1-0-9c814d9362f6@valla.it

---
Francesco Valla (3):
      drm/draw: add drm_draw_can_convert_from_xrgb8888
      drm/log: avoid WARN when searching for usable format
      drm/panic: avoid WARN when checking format support

 drivers/gpu/drm/clients/drm_log.c   |  2 +-
 drivers/gpu/drm/drm_draw.c          | 29 +++++++++++++++++++++++++++++
 drivers/gpu/drm/drm_draw_internal.h |  2 ++
 drivers/gpu/drm/drm_panic.c         |  2 +-
 4 files changed, 33 insertions(+), 2 deletions(-)
---
base-commit: 3a8660878839faadb4f1a6dd72c3179c1df56787
change-id: 20251003-drm_draw_conv_check-9cc3050ebd57

Best regards,
-- 
Francesco Valla <francesco@...la.it>