Re: [PATCH] iio: proximity: sx9324: Correct proximity channel resolution

[Andy Shevchenko <andriy.shevchenko@intel.com>]

On Tue, Aug 18, 2026 at 03:28:03PM +0800, Zhang Jie wrote:
> The proximity channels were previously defined with 12 realbits.
> However, PROXDIFF is read from RegDiffMsb (0x65) and RegDiffLsb
> (0x66). The SX9324 datasheet assigns bits 7:0 of each register to
> PROXDIFF and documents it as a signed two's-complement value
> (Revision 3, Section 8, Table 8, page 43). In contrast, RegOffsetMsb
> explicitly marks bits 7:6 as reserved. Thus, PROXDIFF is a 16-bit
> signed value.
> 
> With realbits = 12, sx_common_read_proximity() uses bit 11 as the
> sign bit in sign_extend32(), causing samples outside the 12-bit
> signed range to wrap into the [-2048, 2047] range.
> 
> Correct the realbits value to 16 to accurately reflect the hardware.

> Tested on an SX9324-based device: a phase 0 DIFF readback of 0x7fff
> was reported as -1 before this change and as 32767 afterward.

Yeah, there seems only Chromebook devices (in ACPI world), MediaTek and
Qualcomm (in DT world). Do we have anybody from Qualcomm to test this?

Hans, I think you (or somebody you might know at QCOMM) might be interested
in this fix.

From the datasheet shared I see the same as described in this commit
and since it was tested on real devices I'm quite sure this is the case.
Reviewed-by: Andy Shevchenko <andriy.shevchenko@intel.com>

> Fixes: 4c18a890dff8 ("iio:proximity:sx9324: Add SX9324 support")
> Cc: stable@vger.kernel.org
> Signed-off-by: Zhang Jie <zhangjie14@huaqin.corp-partner.google.com>
> ---
>  drivers/iio/proximity/sx9324.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/iio/proximity/sx9324.c b/drivers/iio/proximity/sx9324.c
> index 36c45d101336..de6176fd8d47 100644
> --- a/drivers/iio/proximity/sx9324.c
> +++ b/drivers/iio/proximity/sx9324.c
> @@ -223,7 +223,7 @@ static const struct iio_chan_spec_ext_info sx9324_channel_ext_info[] = {
>  	.scan_index = idx,					 \
>  	.scan_type = {						 \
>  		.sign = 's',					 \
> -		.realbits = 12,					 \
> +		.realbits = 16,					 \
>  		.storagebits = 16,				 \
>  		.endianness = IIO_BE,				 \
>  	},							 \

-- 
With Best Regards,
Andy Shevchenko