Re: [Freedreno] [PATCH v3 06/10] drm/msm/dsi: Migrate to drm_dsc_compute_rc_parameters()

[Abhinav Kumar]

On 10/9/2022 11:50 AM, Marijn Suijten wrote:
> As per the FIXME this code is entirely duplicate with what is already
> provided inside drm_dsc_compute_rc_parameters(), and it is yet unknown
> why this comment was put in place instead of resolved from the get-go.
> Not only does it save on duplication, it would have also spared certain
> issues.
>
> For example, this code from downstream assumed dsc->bits_per_pixel to
> contain an integer value, whereas the upstream drm_dsc_config struct has
> it with 4 fractional bits.  drm_dsc_compute_rc_parameters() already
> accounts for this feat, and the sole remaining use of
> dsc->bits_per_pixel inside dsi_populate_dsc_params() will be addressed
> in a separate patch.

This is a nice cleanup! Thanks for doing this. I would actually like to 
move towards the drm_dsc_compute_rc_parameters() API.

But I would like to hold back this change till Vinod clarifies because 
Vinod had mentioned that with drm_dsc_compute_rc_parameters() he was 
seeing a mismatch in the computation of two values.

slice_bpg_offset and the final_offset.

The difference between the upstream drm_dsc_compute_rc_parameters() and 
dsi_populate_dsc_params() causing this was not clear to me from his 
explanation earlier.

So this was left as a to-do item.

I would like this to be re-tested on pixel3 and check if this works for 
vinod. If not, i think its the right time to debug why and not delay 
this more.

Thanks

Abhinav
> Fixes: b9080324d6ca ("drm/msm/dsi: add support for dsc data")
> Signed-off-by: Marijn Suijten <marijn.suijten@xxxxxxxxxxxxxx>
> ---
>   drivers/gpu/drm/msm/dsi/dsi_host.c | 64 +++---------------------------
>   1 file changed, 6 insertions(+), 58 deletions(-)
>
> diff --git a/drivers/gpu/drm/msm/dsi/dsi_host.c b/drivers/gpu/drm/msm/dsi/dsi_host.c
> index 83cde4d62b68..68c39debc22f 100644
> --- a/drivers/gpu/drm/msm/dsi/dsi_host.c
> +++ b/drivers/gpu/drm/msm/dsi/dsi_host.c
> @@ -21,6 +21,7 @@
>   
>   #include <video/mipi_display.h>
>   
> +#include <drm/display/drm_dsc_helper.h>
>   #include <drm/drm_of.h>
>   
>   #include "dsi.h"
> @@ -1771,14 +1772,6 @@ static char bpg_offset[DSC_NUM_BUF_RANGES] = {
>   
>   static int dsi_populate_dsc_params(struct drm_dsc_config *dsc)
>   {
> -	int mux_words_size;
> -	int groups_per_line, groups_total;
> -	int min_rate_buffer_size;
> -	int hrd_delay;
> -	int pre_num_extra_mux_bits, num_extra_mux_bits;
> -	int slice_bits;
> -	int data;
> -	int final_value, final_scale;
>   	int i;
>   
>   	dsc->rc_model_size = 8192;
> @@ -1804,11 +1797,11 @@ static int dsi_populate_dsc_params(struct drm_dsc_config *dsc)
>   	if (dsc->bits_per_pixel != 8)
>   		dsc->initial_offset = 2048;	/* bpp = 12 */
>   
> -	mux_words_size = 48;		/* bpc == 8/10 */
> -	if (dsc->bits_per_component == 12)
> -		mux_words_size = 64;
> +	if (dsc->bits_per_component <= 10)
> +		dsc->mux_word_size = DSC_MUX_WORD_SIZE_8_10_BPC;
> +	else
> +		dsc->mux_word_size = DSC_MUX_WORD_SIZE_12_BPC;
>   
> -	dsc->mux_word_size = mux_words_size;
>   	dsc->initial_xmit_delay = 512;
>   	dsc->initial_scale_value = 32;
>   	dsc->first_line_bpg_offset = 12;
> @@ -1820,52 +1813,7 @@ static int dsi_populate_dsc_params(struct drm_dsc_config *dsc)
>   	dsc->rc_quant_incr_limit0 = 11;
>   	dsc->rc_quant_incr_limit1 = 11;
>   
> -	/* FIXME: need to call drm_dsc_compute_rc_parameters() so that rest of
> -	 * params are calculated
> -	 */
> -	groups_per_line = DIV_ROUND_UP(dsc->slice_width, 3);
> -	dsc->slice_chunk_size = DIV_ROUND_UP(dsc->slice_width * dsc->bits_per_pixel, 8);
> -
> -	/* rbs-min */
> -	min_rate_buffer_size =  dsc->rc_model_size - dsc->initial_offset +
> -				dsc->initial_xmit_delay * dsc->bits_per_pixel +
> -				groups_per_line * dsc->first_line_bpg_offset;
> -
> -	hrd_delay = DIV_ROUND_UP(min_rate_buffer_size, dsc->bits_per_pixel);
> -
> -	dsc->initial_dec_delay = hrd_delay - dsc->initial_xmit_delay;
> -
> -	dsc->initial_scale_value = 8 * dsc->rc_model_size /
> -				       (dsc->rc_model_size - dsc->initial_offset);
> -
> -	slice_bits = 8 * dsc->slice_chunk_size * dsc->slice_height;
> -
> -	groups_total = groups_per_line * dsc->slice_height;
> -
> -	data = dsc->first_line_bpg_offset * 2048;
> -
> -	dsc->nfl_bpg_offset = DIV_ROUND_UP(data, (dsc->slice_height - 1));
> -
> -	pre_num_extra_mux_bits = 3 * (mux_words_size + (4 * dsc->bits_per_component + 4) - 2);
> -
> -	num_extra_mux_bits = pre_num_extra_mux_bits - (mux_words_size -
> -			     ((slice_bits - pre_num_extra_mux_bits) % mux_words_size));
> -
> -	data = 2048 * (dsc->rc_model_size - dsc->initial_offset + num_extra_mux_bits);
> -	dsc->slice_bpg_offset = DIV_ROUND_UP(data, groups_total);
> -
> -	data = dsc->initial_xmit_delay * dsc->bits_per_pixel;
> -	final_value =  dsc->rc_model_size - data + num_extra_mux_bits;
> -	dsc->final_offset = final_value;
> -
> -	final_scale = 8 * dsc->rc_model_size / (dsc->rc_model_size - final_value);
> -
> -	data = (final_scale - 9) * (dsc->nfl_bpg_offset + dsc->slice_bpg_offset);
> -	dsc->scale_increment_interval = (2048 * dsc->final_offset) / data;
> -
> -	dsc->scale_decrement_interval = groups_per_line / (dsc->initial_scale_value - 8);
> -
> -	return 0;
> +	return drm_dsc_compute_rc_parameters(dsc);
>   }
>   
>   static int dsi_host_parse_dt(struct msm_dsi_host *msm_host)