Re: [PATCH v9 02/13] drm/mediatek: Implement Display Stream Compression support

[Chaoyi Chen <chaoyi.chen@rock-chips.com>]

Hi,

On 9/16/2026 7:08 PM, AngeloGioacchino Del Regno wrote:
> Add a real driver for the Display Stream Compression (DSC) Display
> Controller IP, implementing support for DSC v1.1 to v1.2.
> 
> In order to do this, it was necessary to remove the basic DSC IP
> bypass setup from mtk_ddp_comp: this functionality is retained in
> the new mtk_disp_dsc driver, which checks if DSC was actually
> requested by other components (with the only one that currently
> supports this being DSI) and, if not, it will set BYPASS mode in
> the DSC IP.
> 
> Like before, the BYPASS mode is set before starting the DSC IP,
> but unlike before, this is being done in the component start
> callback instead of the config one.
> Notably, the config callback is called by mtk_crtc always
> immediately before the calling start callback, so the order of
> register writes is retained.
> The only real difference is that now this is being done through
> CPU writes instead of CMDQ, but since that's called only once
> and since it's just three registers, the performance impact will
> not be minimal and not even measurable.
> 
> As anticipated, DSC handling was also introduced in the mtk_dsi
> driver: when performing dsi_host_attach, the driver now checks
> if the DSI panel adds the DSC configuration structure to the
> mipi_dsi_device structure and, if it does, it will store a
> pointer in the driver-local mtk_dsi structure's `dsc` member.
> 
> The DSI driver will then check whether the DSC configuration
> that comes from the panel is valid (in regard to MediaTek DSI)
> and will call the DRM API's DSC helpers to calculate and set
> all of the const and RC parameters for the actual DSC setup.
> 
> For the time being, even though the latest MediaTek SoCs do
> support DSC v1.2, only DSC v1.1 pre-scr support is implemented
> as an initial contribution (which is rather big, and 1.2 would
> make it even bigger - but that can anyway be implemented later).
> 
> As a last step for validation of DSC parameters in DSI, a check
> for the hdisplay against DSC slice sidth and one for vdisplay
> against DSC slice height was added to the mode_valid callback,
> making sure that H/V are, as expected, multiples of slice W/H.
> 
> Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
> ---
>  drivers/gpu/drm/mediatek/Makefile       |   1 +
>  drivers/gpu/drm/mediatek/mtk_crtc.c     |  21 ++
>  drivers/gpu/drm/mediatek/mtk_ddp_comp.c |  43 +--
>  drivers/gpu/drm/mediatek/mtk_ddp_comp.h |   9 +
>  drivers/gpu/drm/mediatek/mtk_disp_drv.h |   8 +
>  drivers/gpu/drm/mediatek/mtk_disp_dsc.c | 449 ++++++++++++++++++++++++
>  drivers/gpu/drm/mediatek/mtk_drm_drv.c  |   2 +
>  drivers/gpu/drm/mediatek/mtk_drm_drv.h  |   1 +
>  drivers/gpu/drm/mediatek/mtk_dsi.c      | 151 +++++++-
>  9 files changed, 635 insertions(+), 50 deletions(-)
>  create mode 100644 drivers/gpu/drm/mediatek/mtk_disp_dsc.c
> 

[...]

> +
> +	dsc->simple_422 = false;
> +	dsc->convert_rgb = true;
> +	dsc->vbr_enable = false;
> +
> +	drm_dsc_set_const_params(dsc);
> +	drm_dsc_set_rc_buf_thresh(dsc);
> +
> +	ret = drm_dsc_setup_rc_params(dsc, DRM_DSC_1_2_444);
> +	if (ret) {
> +		dev_err(dev, "Cannot find DSC RC params\n");
> +		return ret;
> +	}
> +

Just out of curiosity, is there a reason the DSC v1.1 rc parameters 
aren't used here?

-- 
Best, 
Chaoyi