linux-kernel - Re: [PATCH v2] ims-pcu: Add commands supported by the new version of the FW

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Date:	Fri, 3 Jan 2014 21:03:11 -0800
From:	Andrey Smirnov <andrew.smirnov@...il.com>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:	linux-input@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] ims-pcu: Add commands supported by the new version of
 the FW

On Fri, Jan 3, 2014 at 8:44 PM, Dmitry Torokhov
<dmitry.torokhov@...il.com> wrote:
> On Fri, Jan 03, 2014 at 08:24:17PM -0800, Andrey Smirnov wrote:
>> On Fri, Jan 3, 2014 at 5:39 PM, Dmitry Torokhov
>> <dmitry.torokhov@...il.com> wrote:
>> > Hi Andrey,
>> >
>> > On Wed, Jan 01, 2014 at 04:47:01PM -0800, Andrey Smirnov wrote:
>> >> New version of the PCU firmware supports two new commands:
>> >>   - IMS_PCU_CMD_OFN_SET_CONFIG which allows to write data to the
>> >>   registers of one finger navigation(OFN) chip present on the device
>> >>   - IMS_PCU_CMD_OFN_GET_CONFIG which allows to read data form the
>> >>   registers of said chip.
>> >>
>> >> This commit adds two helper functions to use those commands and sysfs
>> >> attributes to use them. It also exposes some OFN configuration
>> >> parameters via sysfs.
>> >
>> > Thank you for making the changes. I do not still quite like the games we
>> > play with the OFN attributes, how about the patch below (on top of
>> > yours)?
>> >
>>
>> Yeah, I agree I like it the "two separate sysfs groups" group approach
>> better. The only small nitpick about your patch is that I think we
>> should use "get_unaligned_le16" instead of "le16_to_cpup"(In case
>> anyone decides to run the driver on SuperH or C6x DSPs from TI :-)).
>> Let me test it and if everything works as expected I'll apply you
>> patch, convert it to "get_unaligned_le16", squash and send v3 of the
>> patch.
>
> Why do we need get_unaligned_le16()? As far as I can see pcu->cmd_buf is
> aligned and therefore pcu->cmd_buf[2] is also aligned on word boundary.

* The "pcu" structure is allocated with kmalloc which doesn't give any
guarantees about address alignment.
* I am not sure if the cmd_buf field in that structure is aligned, and
even if it is, any future changes to that structure may shift its
offset.
* Also even if the data we are interested in is aligned on 2-byte
border, I think all those architectures require 4-byte border
alignment.

>
> Thanks.
>
> --
> Dmitry
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