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

[Neil Armstrong]

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