linux-kernel - Re: [PATCH RFC 03/10] drm/panel: Add LGD panel driver for Sony Xperia XZ3

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Date:   Tue, 30 May 2023 01:36:39 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Marijn Suijten <marijn.suijten@...ainline.org>
Cc:     Neil Armstrong <neil.armstrong@...aro.org>,
        Sam Ravnborg <sam@...nborg.org>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Caleb Connolly <caleb@...nolly.tech>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        ~postmarketos/upstreaming@...ts.sr.ht,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...ainline.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Martin Botka <martin.botka@...ainline.org>,
        Jami Kettunen <jami.kettunen@...ainline.org>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        Kuogee Hsieh <quic_khsieh@...cinc.com>,
        Jessica Zhang <quic_jesszhan@...cinc.com>
Subject: Re: [PATCH RFC 03/10] drm/panel: Add LGD panel driver for Sony Xperia
 XZ3

On 30/05/2023 00:11, Marijn Suijten wrote:
> On 2023-05-22 04:16:20, Dmitry Baryshkov wrote:
> <snip>
>>> +	if (ctx->dsi->dsc) {
>>
>> dsi->dsc is always set, thus this condition can be dropped.
> 
> I want to leave room for possibly running the panel without DSC (at a
> lower resolution/refresh rate, or at higher power consumption if there
> is enough BW) by not assigning the pointer, if we get access to panel
> documentation: probably one of the magic commands sent in this driver
> controls it but we don't know which.

This sounds like 'a possible room for expansion' which might never be 
actually used. I think, if we ever get such information or when the 
panel's DSC config gets variadic following the mode, we can reintroduce 
this check.

> 
>>> +		drm_dsc_pps_payload_pack(&pps, ctx->dsi->dsc);
>>> +
>>> +		ret = mipi_dsi_picture_parameter_set(ctx->dsi, &pps);
>>> +		if (ret < 0) {
>>> +			dev_err(panel->dev, "failed to transmit PPS: %d\n", ret);
>>> +			goto fail;
>>> +		}
>>> +		ret = mipi_dsi_compression_mode(ctx->dsi, true);
>>> +		if (ret < 0) {
>>> +			dev_err(dev, "failed to enable compression mode: %d\n", ret);
>>> +			goto fail;
>>> +		}
>>> +
>>> +		msleep(28);
>>> +	}
>>> +
>>> +	ctx->prepared = true;
>>> +	return 0;
>>> +
>>> +fail:
>>> +	gpiod_set_value_cansleep(ctx->reset_gpio, 0);
>>> +	regulator_disable(ctx->vddio);
>>> +	return ret;
>>> +}
> <snip>
>>> +	/* This panel only supports DSC; unconditionally enable it */

-- 
With best wishes
Dmitry