Re: [PATCH 2/4] drm/hibmc: Fix list of formats on the primary plane

[Yongbang Shi <shiyongbang@huawei.com>]

> Remove all formats from the primary plane that are unsupported for
> various reasons.
> 
> * Formats with alpha channel: planes should not announce alpha channels
> unless they support transparency. There's no transparency support in
> the primary plane's implementation.
> 
> * Formats with BGR order. The common format is in RGB channel order.
> There's no BGR support in the primary plane's implementation.
> 
> * RGB888: atomic_update programs the format from cpp[0] * 8 / 16. For
> RGB888's cpp value of 3 this returns 1.5; rounded to 1. Programming
> the value of 1 to HIBMC_CRT_DISP_CTL_FORMAT sets up RGB565. Hence, the
> output is distorted. This can be tested by booting with video=1024x768-24.
> 

I tested this method and was able to reproduce the issue. Thank you for
pointing it out.


> Removing all unsupported formats leaves XRGB8888 and RGB565. Both of
> which are supported and work correctly.
> 

You're right, I checked the DataSheet and confirmed that it only
supports RGB565 and XRGB8888.

Also, I looked at the commit history, and this format was already
present in the first version of the hibmc driver. This is a historic
issue, and it's a bit difficult to determine why it was implemented this
way.


> Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
> Fixes: da52605eea8f ("drm/hisilicon/hibmc: Add support for display engine")
> Cc: Rongrong Zou <zourongrong@gmail.com>
> Cc: Sean Paul <seanpaul@chromium.org>
> Cc: Xinliang Liu <xinliang.liu@linaro.org>
> Cc: Dmitry Baryshkov <lumag@kernel.org>
> Cc: Yongbang Shi <shiyongbang@huawei.com>
> Cc: Baihan Li <libaihan@huawei.com>
> Cc: <stable@vger.kernel.org> # v4.10+
> ---
>  drivers/gpu/drm/hisilicon/hibmc/hibmc_drm_de.c | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/hisilicon/hibmc/hibmc_drm_de.c b/drivers/gpu/drm/hisilicon/hibmc/hibmc_drm_de.c
> index 8fa2a95bcdd1..c4f9ebd9250d 100644
> --- a/drivers/gpu/drm/hisilicon/hibmc/hibmc_drm_de.c
> +++ b/drivers/gpu/drm/hisilicon/hibmc/hibmc_drm_de.c
> @@ -118,10 +118,8 @@ static void hibmc_plane_atomic_update(struct drm_plane *plane,
>  }
>  
>  static const u32 channel_formats1[] = {
> -	DRM_FORMAT_RGB565, DRM_FORMAT_BGR565, DRM_FORMAT_RGB888,
> -	DRM_FORMAT_BGR888, DRM_FORMAT_XRGB8888, DRM_FORMAT_XBGR8888,
> -	DRM_FORMAT_RGBA8888, DRM_FORMAT_BGRA8888, DRM_FORMAT_ARGB8888,
> -	DRM_FORMAT_ABGR8888
> +	DRM_FORMAT_XRGB8888,
> +	DRM_FORMAT_RGB565,
>  };
>  
>  static const struct drm_plane_funcs hibmc_plane_funcs = {

Reviewed-by: Yongbang Shi <shiyongbang@huawei.com>