linux-kernel - Re: [PATCH v4 10/10] drm/vs: add simple dsi encoder

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Message-ID: <b7cgvgh3uphpa3byf3bdl5i4fr64zzuagxg5txuwx7woy56dkt@uhclfjtzejfc>
Date: Mon, 24 Jun 2024 00:11:10 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Keith Zhao <keith.zhao@...rfivetech.com>
Cc: "andrzej.hajda@...el.com" <andrzej.hajda@...el.com>, 
	"neil.armstrong@...aro.org" <neil.armstrong@...aro.org>, "rfoss@...nel.org" <rfoss@...nel.org>, 
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	"p.zabel@...gutronix.de" <p.zabel@...gutronix.de>, Jack Zhu <jack.zhu@...rfivetech.com>, 
	Shengyang Chen <shengyang.chen@...rfivetech.com>, 
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>, "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>, 
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	"linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v4 10/10] drm/vs: add simple dsi encoder

On Sun, Jun 23, 2024 at 07:17:09AM GMT, Keith Zhao wrote:
> Hi Dmitry:
> 
> > On Tue, May 21, 2024 at 06:58:17PM +0800, keith wrote:

> > > +								  "starfive,syscon",
> > > +								  2, args);
> > > +
> > > +	if (IS_ERR(simple->dss_regmap)) {
> > > +		return dev_err_probe(dev, PTR_ERR(simple->dss_regmap),
> > > +				     "getting the regmap failed\n");
> > > +	}
> > > +
> > > +	simple->offset = args[0];
> > > +	simple->mask = args[1];
> > 
> > Is the value that you've read platform dependent or use case dependent?
> > What is the actual value being written? Why are you using syscon for it?
> 
> The syscon is used to select crtcs binded with encoder,
> If this encoder binds to crtc0 , set the syscon reg bit0 = 1
> If this encoder binds to crtc1 , set the syscon reg bit1 = 1 (0x2)
> Maybe I can do this by the possible_crtc instead of using args from dts

If this is a constant between your platforms, it should not be a part of
DT.

> 
> 
> > 
> > > +
> > > +	return 0;
> > > +}
> > > +
> > > +static void vs_encoder_atomic_enable(struct drm_encoder *encoder,
> > > +struct drm_atomic_state *state) {
> > > +	struct vs_simple_encoder *simple = to_simple_encoder(encoder);
> > > +
> > > +	regmap_update_bits(simple->dss_regmap, simple->offset, simple->mask,
> > > +simple->mask);
> > 
> > 
> > A purist in me would ask to have separate mask and value to write.
> Understand , will avoid this action 
> > 
> > > +}
> > 
> > Is it necessary to clear those bits when stopping the stream?
> No need to do this , if clear those bits , the encoder will point to a unknown crtc

what are the consequences? Is it desirable or not?

-- 
With best wishes
Dmitry