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

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Message-ID: <617c8f8a-1fc7-c6a0-eaa5-ce75ff2adc1b@linaro.org>
Date:   Tue, 30 May 2023 09:24:24 +0200
From:   Neil Armstrong <neil.armstrong@...aro.org>
To:     Marijn Suijten <marijn.suijten@...ainline.org>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Caleb Connolly <caleb@...nolly.tech>,
        Jessica Zhang <quic_jesszhan@...cinc.com>
Cc:     Sam Ravnborg <sam@...nborg.org>, David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        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>
Subject: Re: [PATCH RFC 03/10] drm/panel: Add LGD panel driver for Sony Xperia
 XZ3

Hi Marijn, Dmitry, Caleb, Jessica,

On 29/05/2023 23:11, 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.

I'd like to investigate if DSC should perhaps only be enabled if we
run non certain platforms/socs ?

I mean, we don't know if the controller supports DSC and those particular
DSC parameters so we should probably start adding something like :

static drm_dsc_config dsc_params_qcom = {}

static const struct of_device_id panel_of_dsc_params[] = {
	{ .compatible = "qcom,sm8150", , .data = &dsc_params_qcom },
	{ .compatible = "qcom,sm8250", , .data = &dsc_params_qcom },
	{ .compatible = "qcom,sm8350", , .data = &dsc_params_qcom },
	{ .compatible = "qcom,sm8450", , .data = &dsc_params_qcom },
};

...
static int sony_akatsuki_lgd_probe(struct mipi_dsi_device *dsi)
...
	const struct of_device_id *match;

...
	match = of_match_node(panel_of_dsc_params, of_root);
	if (match && match->data) {
		dsi->dsc = devm_kzalloc(&dsi->dev, sizeof(*dsc), GFP_KERNEL);
		memcpy(dsi->dsc, match->data, sizeof(*dsc));
	} else {
		dev_warn(&dsi->dev, "DSI controller is not marked as supporting DSC\n");
	}
...
}

and probably bail out if it's a DSC only panel.

We could alternatively match on the DSI controller's dsi->host->dev instead of the SoC root compatible.

Neil

> 
>>> +		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 */
> 
> On that note I should perhaps reword this.
> 
>>> +	dsi->dsc = dsc = devm_kzalloc(&dsi->dev, sizeof(*dsc), GFP_KERNEL);
>>
>> I think double assignments are frowned upon.
> 
> Ack.
> 
>>
>>> +	if (!dsc)
>>> +		return -ENOMEM;
>>> +
>>> +	dsc->dsc_version_major = 1;
>>> +	dsc->dsc_version_minor = 1;
>>> +
>>> +	dsc->slice_height = 32;
>>> +	dsc->slice_count = 2;
>>> +	// TODO: Get hdisplay from the mode
>>
>> Would you like to fix the TODO?
> 
> I can't unless either migrating to drm_bridge (is that doable?) or
> expand drm_panel.  That's a larger task, but I don't think this driver
> is the right place to track that desire.  Should I drop the comment
> entirely or reword it?
> 
>>> +	WARN_ON(1440 % dsc->slice_count);
>>> +	dsc->slice_width = 1440 / dsc->slice_count;
> 
> <snip>
> 
> - Marijn