linux-kernel - Re: [PATCH 06/20] Input: atmel_mxt_ts - allow writing to object sysfs entry

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Date:	Mon, 19 Mar 2012 16:26:21 +0800
From:	Daniel Kurtz <djkurtz@...omium.org>
To:	Henrik Rydberg <rydberg@...omail.se>
Cc:	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Joonyoung Shim <jy0922.shim@...sung.com>,
	Iiro Valkonen <iiro.valkonen@...el.com>,
	linux-input@...r.kernel.org, linux-kernel@...r.kernel.org,
	Benson Leung <bleung@...omium.org>,
	Yufeng Shen <miletus@...omium.org>
Subject: Re: [PATCH 06/20] Input: atmel_mxt_ts - allow writing to object sysfs entry

On Mon, Mar 19, 2012 at 4:04 PM, Henrik Rydberg <rydberg@...omail.se> wrote:
>
> Hi Daniel,
>
> > Userspace can write a 24-bit value (encoded as a 6 character hex string)
> > to the 'object' sysfs entry to modify a single byte of the object table.
> > The hex string encodes a 3 bytes, in the following format:
> >  TTFFVV
> >
> > Where:
> >  TT = object type
> >  FF = object offset
> >  VV = byte value
> >
> > The object table is modified in device ram, which means the change is
> > volatile, and will be overwritten on the next device reset.  To make
> > changes permanent, the new settings should be persisted in the device's
> > Non-Voltatile Memory using the updatenv sysfs entry.
> >
> > Also, since the device driver initializes itself by reading some values
> > from the object table, the entire driver may need to be unloaded and
> > reloaded after writing the values for the driver to stay in sync.
> >  Whether
> > this is required depends on exactly which values were updated.
> >
> > Signed-off-by: Daniel Kurtz <djkurtz@...omium.org>
> > ---
>
> Perhaps you could give an example of why this is needed?
>
> Thanks,
> Henrik

The idea is to allow a a device to be calibrated via userspace.  The
atmel devices have many registers for tuning properties of their
firmware.
This would be used, for example, to program an initial calibration on
a factory floor, or, to tune a device at runtime.  Currently, the only
way devices are configured and calibrated is for a system integrator
to embed the entire calibration in the kernel via a binary blob in
platform_data.

Thanks,
-Daniel
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