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

From: Dmitry Torokhov <dmitry.torokhov@gmail.com>
To: Raveendra Padasalagi <raveendra.padasalagi@broadcom.com>
Cc: Rob Herring <robh@kernel.org>,
	Russell King <linux@arm.linux.org.uk>,
	Arnd Bergmann <arnd@arndb.de>,
	devicetree@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
	linux-input@vger.kernel.org, Pawel Moll <pawel.moll@arm.com>,
	Mark Rutland <mark.rutland@arm.com>,
	Ian Campbell <ijc+devicetree@hellion.org.uk>,
	Kumar Gala <galak@codeaurora.org>,
	Jonathan Richardson <jonathar@broadcom.com>,
	Jon Mason <jonmason@broadcom.com>,
	Florian Fainelli <f.fainelli@gmail.com>,
	Anup Patel <anup.patel@broadcom.com>, Ray Jui <rjui@broadcom.com>,
	Scott Branden <sbranden@broadcom.com>,
	linux-kernel@vger.kernel.org,
	bcm-kernel-feedback-list@broadcom.com
Subject: Re: [PATCH v2 1/3] input: cygnus-update touchscreen dt node document
Date: Mon, 22 Feb 2016 11:36:04 -0800	[thread overview]
Message-ID: <20160222193604.GA26177@dtor-ws> (raw)
In-Reply-To: <CAAFb_vq6_uQbcWvwV8TZqVqH_C-ueUd+gBRA=mXUQrWqxoz=ww@mail.gmail.com>

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@kernel.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@broadcom.com>
> >> Reviewed-by: Ray Jui <ray.jui@broadcom.com>
> >> Reviewed-by: Scott Branden <scott.branden@broadcom.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