linux-kernel - Re: [PATCH 10/53] Input: atmel_mxt_ts - Add memory access interface via sysfs

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Message-ID: <1717403.GgHsbyUkDZ@dtor-d630.eng.vmware.com>
Date:	Wed, 05 Jun 2013 12:04:37 -0700
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	Nick Dyer <nick.dyer@...ev.co.uk>
Cc:	Daniel Kurtz <djkurtz@...omium.org>,
	Henrik Rydberg <rydberg@...omail.se>,
	Joonyoung Shim <jy0922.shim@...sung.com>,
	Alan.Bowens@...el.com, linux-input@...r.kernel.org,
	linux-kernel@...r.kernel.org, pmeerw@...erw.net,
	bleung@...omium.org, olofj@...omium.org
Subject: Re: [PATCH 10/53] Input: atmel_mxt_ts - Add memory access interface via sysfs

On Wednesday, June 05, 2013 07:45:04 PM Nick Dyer wrote:
> Dmitry Torokhov wrote:
> > On Wednesday, June 05, 2013 06:37:03 PM Nick Dyer wrote:
> >> Atmel maXTouch chips can be addressed via an "Object Based Protocol"
> >> which
> >> defines how i2c registers are mapped to different functions within the
> >> chips. This interface exposes the register map and allows user-space
> >> utilities to inspect and alter object configuration, and to view
> >> diagnostic
> >> data, while the device is running.
> > 
> > I think if the driver was to use regmap then this fucntionality will
> > already be there as regmap exports registers via debugfs.
> 
> Yes, this was suggested in the past and I spent some time looking into it.
> 
> We have made a deliberate choice to implement this via sysfs rather than
> debugfs since it needs to work on devices that don't have debugfs enabled.

Then they will have to enable it. Re-implementing something because
someone might not enable needed subsystem is not a good idea. Let's
say somebody disabled I2C - will you write your own implementation because
of that? Of course not, you just say that for given functionality it
is a prerequisite.

> 
> In addition, there are some quirks about the way in which we have to
> read/write registers which means regmap isn't a good fit.

Could you please elaborate more on this?

Thanks.

-- 
Dmitry
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