linux-kernel - Re: [PATCH] iio: proximity: hx9023s: fix scan

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Message-ID: <795dffe0-51cf-49a8-bbb1-1585edddf5ba@baylibre.com>
Date: Wed, 23 Jul 2025 09:29:37 -0500
From: David Lechner <dlechner@...libre.com>
To: Andy Shevchenko <andriy.shevchenko@...el.com>
Cc: Jonathan Cameron <jic23@...nel.org>, Nuno Sá
 <nuno.sa@...log.com>, Andy Shevchenko <andy@...nel.org>,
 Yasin Lee <yasin.lee.x@...il.com>, linux-iio@...r.kernel.org,
 linux-kernel@...r.kernel.org, Jonathan Cameron <Jonathan.Cameron@...wei.com>
Subject: Re: [PATCH] iio: proximity: hx9023s: fix scan_type endianness

On 7/23/25 9:13 AM, Andy Shevchenko wrote:
> On Tue, Jul 22, 2025 at 06:08:37PM -0500, David Lechner wrote:
>> On 7/22/25 6:07 PM, David Lechner wrote:
>>> Change the scan_type endianness from IIO_BE to IIO_LE. This matches
>>> the call to cpu_to_le16() in hx9023s_trigger_handler() that formats
>>> the data before pushing it to the IIO buffer.
> 
>> It is odd to have data already in CPU-endian and convert it to LE
>> before pushing to buffers. So I'm a bit tempted to do this instead
>> since it probably isn't likely anyone is using this on a big-endian
>> system:
> 
> I can say that first of all, we need to consult with the datasheet for the
> actual HW endianess. And second, I do not believe that CPU endianess may be
> used, 

Why not? Lot's of IIO drivers use IIO_CPU in their scan buffers.

> I can't imagine when this (discrete?) component can be integrated in such
> a way. That said, I think your second approach even worse.
> 

hx9023s_sample() is calling get_unaligned_le16() on all of the data
read over the bus, so in the driver, all data is stored CPU-endian
already rather than passing actual raw bus data to the buffer.

So it seems a waste of CPU cycles to convert it back to little-endian
to push to the buffer only for consumers to have to convert it back
to CPU-endian again. But since most systems are little-endian already
this doesn't really matter since no actual conversion is done in this
case.