linux-kernel - RE: [PATCH 1/3] input: cygnus-update touchscreen dt node document

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Date:	Tue, 9 Feb 2016 22:25:26 +0530
From:	Raveendra Padasalagi <raveendra.padasalagi@...adcom.com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Russell King <linux@....linux.org.uk>,
	devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-input@...r.kernel.org, Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Jonathan Richardson <jonathar@...adcom.com>,
	Jon Mason <jonmason@...adcom.com>,
	Florian Fainelli <f.fainelli@...il.com>,
	Ray Jui <rjui@...adcom.com>,
	Scott Branden <sbranden@...adcom.com>,
	linux-kernel@...r.kernel.org, bcm-kernel-feedback-list@...adcom.com
Subject: RE: [PATCH 1/3] input: cygnus-update touchscreen dt node document

> -----Original Message-----
> From: Arnd Bergmann [mailto:arnd@...db.de]
> Sent: 09 February 2016 16:34
> To: Raveendra Padasalagi
> Cc: Dmitry Torokhov; Russell King; devicetree@...r.kernel.org;
linux-arm-
> kernel@...ts.infradead.org; linux-input@...r.kernel.org; Rob Herring;
Pawel
> Moll; Mark Rutland; Ian Campbell; Kumar Gala; Jonathan Richardson; Jon
> Mason; Florian Fainelli; Ray Jui; Scott Branden;
linux-kernel@...r.kernel.org;
> bcm-kernel-feedback-list@...adcom.com
> Subject: Re: [PATCH 1/3] input: cygnus-update touchscreen dt node
document
>
> On Tuesday 09 February 2016 14:27:55 Raveendra Padasalagi wrote:
> > +
> > +One of the below 2 property is mandatory.
> > +- ts_syscon: handler of syscon node defining physical base address
> > +  of the controller and length of memory mapped region.
> > +  If this property is selected please make sure MFD_SYSCON config
> > +  is enabled in the defconfig file.
> > +or
> > +- reg: physical base address of the controller and length of memory
> > +  mapped region.
> > +
> >  - clocks:  The clock provided by the SOC to driver the tsc
> >  - clock-name:  name for the clock
> >  - interrupts: The touchscreen controller's interrupt @@ -54,12 +62,16
> > @@ Optional properties:
> >  - touchscreen-inverted-y: Y axis is inverted (boolean)
> >
> >  Example:
> > +       ts_adc_syscon: ts_adc_syscon@...80a6000 {
> > +               compatible = "syscon";
> > +               reg = <0x180a6000 0xc30>;
> > +       };
> >
> >         touchscreen: tsc@...80A6000 {
> >                 compatible = "brcm,iproc-touchscreen";
> >                 #address-cells = <1>;
> >                 #size-cells = <1>;
> > -               reg = <0x180A6000 0x40>;
> > +               syscon = <&ts_adc_syscon>;
> >                 clocks = <&adc_clk>;
> >                 clock-names = "tsc_clk";
> >                 interrupts = <GIC_SPI 164 IRQ_TYPE_LEVEL_HIGH>;
>
> This doesn't seem right: For one thing, it's an incompatible binding
change which
> you should try to avoid.

> Worse, the syscon has a name indicating that it really has a particular
function,
> but the name is completely generic (just "syscon"). Please add a
specific
> compatible string identifying the device that owns the registers, and
put any
> other associated properties (clocks, interrupts, ...) that are for that
device in
> general rather than just the touchscreen in there.

By mistake "syscon" name is documented in "touchscreen" label above. In
the
touchscreen driver code and .dtsi file it's named and used as "ts_syscon".
Please refer https://lkml.org/lkml/2016/2/9/71 for the changes.
Let me know if this ok. I will correct the documentation in the next
patch.

> Your changelog text fails to describe why you do this change in the
first place,
> and why you can't do it in a backward-compatible way, so please rewrite
that
> text.

Yes, I will update the change log in the next patch.

In Cygnus SOC, Touch screen controller registers are shared with ADC and
flex timer IP's.
Using readl/writel could lead to race condition. So this patch is
introduced to take care
mutually exclusive access of register's in such a case.

In the platform's where touchscreen register's are not shared normal
readl/writel
could be used.

Based on the dt  property entry "reg" or "ts_syscon" register accesses are
handled.
if "reg" is provided normal readl/writel API's are used to access
register's else if
"ts_syscon" is provided then syscon API's are used.

> 	Arnd