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

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Date:   Mon, 29 May 2023 23:11:20 +0200
From:   Marijn Suijten <marijn.suijten@...ainline.org>
To:     Dmitry Baryshkov <dmitry.baryshkov@...aro.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 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.

> > +		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