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

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Message-ID: <bdef4aec-f9b1-48d9-874a-2511a0f213de@linaro.org>
Date:   Thu, 6 Oct 2022 00:11:06 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Marijn Suijten <marijn.suijten@...ainline.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 06/10/2022 00:08, Marijn Suijten wrote:
> 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?

I'd say, return -EINVAL or -EOPNOTSUPP for now, let's fix that later. 
It's definitely a separate change. Let's wait for a device with such 
panel to be able to test it.

-- 
With best wishes
Dmitry