linux-kernel - Re: [PATCH v3 05/10] drm/msm/dsi: Appropriately set dsc->mux_word

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Date:   Wed, 12 Oct 2022 15:53:46 -0700
From:   Abhinav Kumar <quic_abhinavk@...cinc.com>
To:     Marijn Suijten <marijn.suijten@...ainline.org>,
        <phone-devel@...r.kernel.org>, Rob Clark <robdclark@...il.com>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Vinod Koul <vkoul@...nel.org>
CC:     <~postmarketos/upstreaming@...ts.sr.ht>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...ainline.org>,
        Konrad Dybcio <konrad.dybcio@...ainline.org>,
        Martin Botka <martin.botka@...ainline.org>,
        Jami Kettunen <jami.kettunen@...ainline.org>,
        Sean Paul <sean@...rly.run>, David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Douglas Anderson <dianders@...omium.org>,
        Vladimir Lypak <vladimir.lypak@...il.com>,
        <linux-arm-msm@...r.kernel.org>, <dri-devel@...ts.freedesktop.org>,
        <freedreno@...ts.freedesktop.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 05/10] drm/msm/dsi: Appropriately set
 dsc->mux_word_size based on bpc



On 10/9/2022 11:48 AM, Marijn Suijten wrote:
> This field is currently unread but will come into effect when duplicated
> code below is migrated to call drm_dsc_compute_rc_parameters(), which
> uses the bpc-dependent value of the local variable mux_words_size in
> much the same way.
> 
> The hardcoded constant seems to be a remnant from the `/* bpc 8 */`
> comment right above, indicating that this group of field assignments is
> applicable to bpc = 8 exclusively and should probably bail out on
> different bpc values, until constants for other bpc values are added (or
> the current ones are confirmed to be correct across multiple bpc's).
> 

Yes, this seems to hard-code it to 8bpc/10bpc. So your code-change is fine.

Reviewed-by: Abhinav Kumar <quic_abhinavk@...cinc.com>
> Fixes: b9080324d6ca ("drm/msm/dsi: add support for dsc data")
> Signed-off-by: Marijn Suijten <marijn.suijten@...ainline.org>
> ---
>   drivers/gpu/drm/msm/dsi/dsi_host.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/msm/dsi/dsi_host.c b/drivers/gpu/drm/msm/dsi/dsi_host.c
> index f42794cdd4c1..83cde4d62b68 100644
> --- a/drivers/gpu/drm/msm/dsi/dsi_host.c
> +++ b/drivers/gpu/drm/msm/dsi/dsi_host.c
> @@ -1808,6 +1808,7 @@ static int dsi_populate_dsc_params(struct drm_dsc_config *dsc)
>   	if (dsc->bits_per_component == 12)
>   		mux_words_size = 64;
>   
> +	dsc->mux_word_size = mux_words_size;
>   	dsc->initial_xmit_delay = 512;
>   	dsc->initial_scale_value = 32;
>   	dsc->first_line_bpg_offset = 12;
> @@ -1818,7 +1819,6 @@ static int dsi_populate_dsc_params(struct drm_dsc_config *dsc)
>   	dsc->flatness_max_qp = 12;
>   	dsc->rc_quant_incr_limit0 = 11;
>   	dsc->rc_quant_incr_limit1 = 11;
> -	dsc->mux_word_size = DSC_MUX_WORD_SIZE_8_10_BPC;
>   
>   	/* FIXME: need to call drm_dsc_compute_rc_parameters() so that rest of
>   	 * params are calculated