linux-kernel - Re: [PATCH v2 1/3] input: cygnus-update touchscreen dt node document

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Date:	Mon, 22 Feb 2016 11:36:04 -0800
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	Raveendra Padasalagi <raveendra.padasalagi@...adcom.com>
Cc:	Rob Herring <robh@...nel.org>,
	Russell King <linux@....linux.org.uk>,
	Arnd Bergmann <arnd@...db.de>, devicetree@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-input@...r.kernel.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>,
	Anup Patel <anup.patel@...adcom.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 v2 1/3] input: cygnus-update touchscreen dt node document

On Fri, Feb 19, 2016 at 11:43:50AM +0530, Raveendra Padasalagi wrote:
> On Thu, Feb 18, 2016 at 8:06 PM, Rob Herring <robh@...nel.org> wrote:
> > On Wed, Feb 17, 2016 at 03:13:44PM +0530, Raveendra Padasalagi wrote:
> >> In Cygnus SOC touch screen controller registers are shared
> >> with ADC and flex timer. Using readl/writel could lead to
> >> race condition. So touch screen driver is enhanced to support
> >>
> >> 1. If touchscreen register's are not shared. Register access
> >> is handled through readl/writel if "brcm,iproc-touchscreen"
> >> compatible is provided in touchscreen dt node. This will help
> >> for future SOC's if comes with dedicated touchscreen IP register's.
> >>
> >> 2. If touchscreen register's are shared with other IP's, register
> >> access is handled through syscon framework API's to take care of
> >> mutually exclusive access. This feature can be enabled by selecting
> >> "brcm,iproc-touchscreen-syscon" compatible string in the touchscreen
> >> dt node.
> >>
> >> Hence touchscreen dt node bindings document is updated to take care
> >> of above changes in the touchscreen driver.
> >>
> >> Signed-off-by: Raveendra Padasalagi <raveendra.padasalagi@...adcom.com>
> >> Reviewed-by: Ray Jui <ray.jui@...adcom.com>
> >> Reviewed-by: Scott Branden <scott.branden@...adcom.com>
> >> ---
> >>  .../input/touchscreen/brcm,iproc-touchscreen.txt   | 57 +++++++++++++++++++---
> >>  1 file changed, 51 insertions(+), 6 deletions(-)
> >>
> >> diff --git a/Documentation/devicetree/bindings/input/touchscreen/brcm,iproc-touchscreen.txt b/Documentation/devicetree/bindings/input/touchscreen/brcm,iproc-touchscreen.txt
> >> index 34e3382..f530c25 100644
> >> --- a/Documentation/devicetree/bindings/input/touchscreen/brcm,iproc-touchscreen.txt
> >> +++ b/Documentation/devicetree/bindings/input/touchscreen/brcm,iproc-touchscreen.txt
> >> @@ -1,12 +1,30 @@
> >>  * Broadcom's IPROC Touchscreen Controller
> >>
> >>  Required properties:
> >> -- compatible: must be "brcm,iproc-touchscreen"
> >> -- reg: physical base address of the controller and length of memory mapped
> >> -  region.
> >> +- compatible: should be one of
> >> +        "brcm,iproc-touchscreen"
> >> +        "brcm,iproc-touchscreen-syscon"
> >
> > More specific and this is not how you do syscon. Either the block is or
> > isn't. You can't have it both ways.
> 
> Existing driver has support for reg, if we modify now to support only syscon
> then this driver will not work if some one wishes to use previous
> kernel version's
> dt and vice versa. Basically this breaks dt compatibility. Is that ok ?

But the issue is that the driver does not actually work correctly with
direct register access on those systems, since the registers are
actually shared with other components. I am not quite sure if it is OK
to break DT binding in this case...

Thanks.

-- 
Dmitry