[PATCH v9 05/17] drm/vkms: Add dummy pixel_read/pixel_write callbacks to avoid NULL pointers

[Louis Chauvet <louis.chauvet@bootlin.com>]

Introduce two callbacks which does nothing. They are used in replacement
of NULL and it avoid kernel OOPS if this NULL is called.

If those callback are used, it means that there is a mismatch between
what formats are announced by atomic_check and what is realy supported by
atomic_update.

Acked-by: Pekka Paalanen <pekka.paalanen@collabora.com>
Signed-off-by: Louis Chauvet <louis.chauvet@bootlin.com>
---
 drivers/gpu/drm/vkms/vkms_formats.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/vkms/vkms_formats.c b/drivers/gpu/drm/vkms/vkms_formats.c
index 5ebc691656bc..ecbe79f8dfdc 100644
--- a/drivers/gpu/drm/vkms/vkms_formats.c
+++ b/drivers/gpu/drm/vkms/vkms_formats.c
@@ -135,6 +135,7 @@ static void RGB565_to_argb_u16(u8 *in_pixel, struct pixel_argb_u16 *out_pixel)
 	out_pixel->b = drm_fixp2int_round(drm_fixp_mul(fp_b, fp_rb_ratio));
 }
 
+
 /**
  * vkms_compose_row - compose a single row of a plane
  * @stage_buffer: output line with the composed pixels
@@ -260,8 +261,10 @@ void vkms_writeback_row(struct vkms_writeback_job *wb,
 
 /**
  * get_pixel_conversion_function() - Retrieve the correct read_pixel function for a specific
- * format. The returned pointer is NULL for unsupported pixel formats. The caller must ensure that
- * the pointer is valid before using it in a vkms_plane_state.
+ * format.
+ *
+ * If the format is not supported by VKMS a warning is emitted and a dummy "always read magenta"
+ * function is returned.
  *
  * @format: DRM_FORMAT_* value for which to obtain a conversion function (see [drm_fourcc.h])
  */
@@ -293,8 +296,8 @@ pixel_read_t get_pixel_read_function(u32 format)
 
 /**
  * get_pixel_write_function() - Retrieve the correct write_pixel function for a specific format.
- * The returned pointer is NULL for unsupported pixel formats. The caller must ensure that the
- * pointer is valid before using it in a vkms_writeback_job.
+ * If the format is not supported by VKMS a warning is emitted and a dummy "don't do anything"
+ * function is returned.
  *
  * @format: DRM_FORMAT_* value for which to obtain a conversion function (see [drm_fourcc.h])
  */

-- 
2.44.2