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

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Message-ID: <aIDzvNYIaJnSuzOa@smile.fi.intel.com>
Date: Wed, 23 Jul 2025 17:37:48 +0300
From: Andy Shevchenko <andriy.shevchenko@...el.com>
To: David Lechner <dlechner@...libre.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 Wed, Jul 23, 2025 at 09:29:37AM -0500, David Lechner wrote:
> 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.

I see, now it makes a lot of sense. Thanks for clarifying this to me.

> 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.

Right, but it's buggy on BE, isn't it?

-- 
With Best Regards,
Andy Shevchenko