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

[Dmitry Baryshkov]

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.
>
> > > +		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?

I'd say, reword it, so that it becomes more obvious why this TODO can 
not be fixed at this moment.

> > > +	WARN_ON(1440 % dsc->slice_count);
> > > +	dsc->slice_width = 1440 / dsc->slice_count;
>
> <snip>
>
> - Marijn

--
With best wishes
Dmitry