linux-kernel - Re: [PATCH v2 5/7] drm/msm/dsi: Account for DSC's bits_per

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Date:   Wed, 5 Oct 2022 23:08:45 +0200
From:   Marijn Suijten <marijn.suijten@...ainline.org>
To:     Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        phone-devel@...r.kernel.org, Rob Clark <robdclark@...il.com>,
        Vinod Koul <vkoul@...nel.org>,
        ~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>,
        Daniel Vetter <daniel@...ll.ch>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        Sean Paul <sean@...rly.run>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Javier Martinez Canillas <javierm@...hat.com>,
        Alex Deucher <alexander.deucher@....com>,
        Douglas Anderson <dianders@...omium.org>,
        Vladimir Lypak <vladimir.lypak@...il.com>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, freedreno@...ts.freedesktop.org,
        David Airlie <airlied@...ux.ie>
Subject: Re: [PATCH v2 5/7] drm/msm/dsi: Account for DSC's bits_per_pixel
 having 4 fractional bits

On 2022-10-05 22:58:48, Marijn Suijten wrote:
> On 2022-10-05 22:31:43, Dmitry Baryshkov wrote:
> > [..]
> > In fact, could you please take a look if we can switch to using this
> > function and drop our code?
>
> [..]
>
> Do you want me to do this in a v3, before applying this fractional-bits
> fix?  [..]

One thing to note:

	/* bpc 8 */
	dsc->flatness_min_qp = 3;
	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;

Here a bunch of properties are hardcoded, seemingly for bpc = 8.
mux_word_size is only ever read in drm_dsc_compute_rc_parameters() so
only becomes relevant _after_ the migration, and is currently dealt with
correctly by:

	mux_words_size = 48;		/* bpc == 8/10 */
	if (dsc->bits_per_component == 12)
		mux_words_size = 64;

Aside fixing that to assign these values (through the proper constants)
to dsc->mux_word_size, is it worth looking for the right parameters for
other bpc or return -EINVAL if bpc isn't 8, to uphold this comment until
support for other bpc is validated?

- Marijn