linux-kernel - Re: [linux-sunxi] Re: [PATCH v3 21/30] iio: adc: sun4i-gpadc-iio: add support for H3 thermal sensor

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Date:   Mon, 03 Sep 2018 19:01:47 +0800
From:   Icenowy Zheng <icenowy@...c.io>
To:     maxime.ripard@...tlin.com,
        Maxime Ripard <maxime.ripard@...tlin.com>
CC:     Philipp Rossak <embed3d@...il.com>, mark.rutland@....com,
        geert+renesas@...der.be, linux-iio@...r.kernel.org,
        robh+dt@...nel.org, linux-sunxi@...glegroups.com,
        clabbe.montjoie@...il.com, pmeerw@...erw.net, lee.jones@...aro.org,
        lars@...afoo.de, quentin.schulz@...tlin.com, linux@...linux.org.uk,
        wens@...e.org, devicetree@...r.kernel.org, arnd@...db.de,
        vilhelm.gray@...il.com, broonie@...nel.org,
        linux-arm-kernel@...ts.infradead.org, rdunlap@...radead.org,
        arnaud.pouliquen@...com, linux-kernel@...r.kernel.org,
        lukas@...ner.de, knaack.h@....de, eugen.hristev@...rochip.com,
        jic23@...nel.org
Subject: Re: [linux-sunxi] Re: [PATCH v3 21/30] iio: adc: sun4i-gpadc-iio: add support for H3 thermal sensor



于 2018年9月3日 GMT+08:00 下午6:20:22, Maxime Ripard <maxime.ripard@...tlin.com> 写到:
>On Fri, Aug 31, 2018 at 05:51:41PM +0800, Icenowy Zheng wrote:
>> Personally I suggest to leave out all SID or calibration related
>> patches here.
>> 
>> Currently we seems to be wrongly converting SID to big endian,
>however,
>> the orgnization of the THS calibration data on H6 shows that it's
>> surely little endian:
>> 
>> It consists a temperature value in 1/10 celsuis as unit, and some
>> thermal register readout values, which are the values read out at the
>> given temperature, and every value here (the temperature and the
>> readout) are all half word length.
>> 
>> Let the temperature value be AABB, the two readout values be XXYY and
>> ZZWW, the oragnization is:
>> BB AA YY XX WW ZZ ** ** .
>> 
>> When converting the SID to big endian, it becomes:
>> XX YY AA BB ** ** ZZ WW ,
>> which is non-sense, and not able to do sub-word cell addressing.
>> 
>> Maxime, should I drop the LE2BE conversion in SID driver? (I doubt
>> whether it will break compatibility.)
>
>This is exposed to the userspace, so no.

Please note the LE2BE totally breaks the SID addressing.

Without it dropped all cells must be referenced with
4 byte word as unit, and half word addressing of
SID is thus not possible. The driver will also need then to split
the half words if needed.

I think this is kind of hardware misbehavior, and not a simple
UAPI change, so the UAPI stability shouldn't affect this change.

>
>Maxime
>>