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

[Nick Dyer <nick.dyer@itdev.co.uk>]

Daniel Kurtz wrote:
> 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@chromium.org>

NAK. I have several concerns about this:

1) The object sysfs entry doesn't follow the sysfs guidelines, this is
abusing it further.
2) Object type can be larger than 1 byte in the future.
3) Your interface restricts you to doing 1 byte writes. What about larger
block sizes?

In short, I think exposing the entire register space as a binary attribute
(the same way that regmap does) is a preferable solution to this
requirement, and we already have user space tools which use it.

cheers

-- 
Nick Dyer
Software Engineer, ITDev Ltd
Hardware and Software Development Consultancy
Website: http://www.itdev.co.uk