On Tue, 5 Oct 2021 17:16:31 -0300 Igor Matheus Andrade Torrente igormtorrente@gmail.com wrote:

XRGB to ARGB behavior

During the development, I decided to always fill the alpha channel of the output pixel whenever the conversion from a format without an alpha channel to ARGB16161616 is necessary. Therefore, I ignore the value received from the XRGB and overwrite the value with 0xFFFF.

My question is, is this behavior acceptable?

Hi,

that is the expected behaviour. X channel values must never affect anything on screen, hence they must never affect other channels' values. You are free to completely ignore X channel values, and if your output buffer has X channel, then you are free to write (or not write, unless for security reasons) whatever into it.

Thanks, pq

[1] https://lists.freedesktop.org/archives/igt-dev/2021-October/036125.html

Igor Matheus Andrade Torrente (6): drm: vkms: Replace the deprecated drm_mode_config_init drm: vkms: Alloc the compose frame using vzalloc drm: vkms: Replace hardcoded value of `vkms_composer.map` to DRM_FORMAT_MAX_PLANES drm: vkms: Add fb information to `vkms_writeback_job` drm: vkms: Prepare `vkms_wb_encoder_atomic_check` to accept multiple formats drm: vkms: Refactor the plane composer to accept new formats

drivers/gpu/drm/vkms/vkms_composer.c | 275 ++++++++++++++------------ drivers/gpu/drm/vkms/vkms_drv.c | 5 +- drivers/gpu/drm/vkms/vkms_drv.h | 12 +- drivers/gpu/drm/vkms/vkms_formats.h | 125 ++++++++++++ drivers/gpu/drm/vkms/vkms_writeback.c | 27 ++- 5 files changed, 304 insertions(+), 140 deletions(-) create mode 100644 drivers/gpu/drm/vkms/vkms_formats.h