From: Alexander Stein <alexander.stein@systec-electronic.com>
To: Stefan Agner <stefan@agner.ch>
Cc: dri-devel@lists.freedesktop.org, shawnguo@kernel.org,
        kernel@pengutronix.de, airlied@linux.ie, daniel.vetter@ffwll.ch,
        jianwei.wang.chn@gmail.com, alison.wang@freescale.com, meng.yi@nxp.com,
        mturquette@baylibre.com, sboyd@codeaurora.org, mark.rutland@arm.com,
        robh+dt@kernel.org, pawel.moll@arm.com, ijc+devicetree@hellion.org.uk,
        galak@codeaurora.org, linux-kernel@vger.kernel.org,
        devicetree@vger.kernel.org, linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v2 6/8] drm/fsl-dcu: add TCON driver
Date: Tue, 29 Mar 2016 09:26:53 +0200
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On Tuesday 29 March 2016 00:11:13, Stefan Agner wrote:
> >> --- a/Documentation/devicetree/bindings/display/fsl,dcu.txt
> >> +++ b/Documentation/devicetree/bindings/display/fsl,dcu.txt
> >> 
> >> @@ -14,6 +14,7 @@ Required properties:
> >>  Optional properties:
> >>  - clocks:		Second handle for pixel clock.
> >>  - clock-names:		Second name "pix" for pixel clock.
> >> 
> >> +- fsl,tcon:		The phandle to the timing controller node.
> > 
> > Maybe a comment this is (currently) only for Vybrid, but not LS1021A.
> 
> IMHO, such references to SoCs in a peripheral binding is somewhat
> misplaced. If we would start doing this, we would end up in lots of SoC
> references, and nobody knows whether they are actually accurate and up
> to date... And I think we should add tcon to LS1021a, more on that
> below...

Well, I don't mind after all.

> >> --- /dev/null
> >> +++ b/drivers/gpu/drm/fsl-dcu/fsl_tcon.c
> >> [...]
> >> +struct fsl_tcon *fsl_tcon_init(struct device *dev)
> >> +{
> >> +	struct fsl_tcon *tcon;
> >> +	struct device_node *np;
> >> +	int ret;
> >> +
> >> +	tcon = devm_kzalloc(dev, sizeof(*tcon), GFP_KERNEL);
> >> +	if (!tcon)
> >> +		return NULL;
> >> +
> >> +	np = of_parse_phandle(dev->of_node, "fsl,tcon", 0);
> >> +	if (!np) {
> >> +		dev_warn(dev, "Couldn't find the tcon node\n");
> >> +		return NULL;
> >> +	}
> > 
> > Maybe check for device tree node before allocating struct fsl_tcon? Also
> > this should not be a warning, as on LS1021A this is to be expected.
> 
> Agreed, definitely the smarter sequence.
> 
> Afact LS1021a has also a TCON. At least in Jianwei Wangs initial patches
> it was part of the driver, see:
> https://lkml.org/lkml/2015/7/13/242
> 
> Not sure how that driver can work without TCON support on LS1021a, maybe
> the bootloader sets the TCON to bypass?
> 
> Since I do not have a LS1021a, I hesitated to just add it to the LS1021s
> dt's, but it should be fairly straight forward.

Interesting, but in Patch 3 (https://lists.freedesktop.org/archives/dri-devel/2015-July/086381.html) no TCON node is added and using is still 
optional. Yet, I don't find any TCON hardware in the LS1021A reference manual, 
e.g. in the memory map. I hard guess is that it doesn't require/use one. 
Without memory address it would be pretty hard to add one.

Alexander