Hi Jonathan,
Jonathan Cameron <jic23@xxxxxxxxxx> wrote on Sun, 6 Oct 2019 11:04:24
+0100:
> On Thu, 3 Oct 2019 19:33:55 +0200
> Miquel Raynal <miquel.raynal@xxxxxxxxxxx> wrote:
>
> > Until now, only write operations were supported. Force two bytes read
> > operation when reading from this register (might be wrong when reading
> > the temperature, but will work with any other value).
>
> That's worrying as comments go. Just return an error on the temperature
> register if it's going to do the wrong thing.
Actually the debugfs_reg_access hook is supposedly stateless. When
reading registers I don't know what I am reading because the "source" is
selected during the write operation, so I have no reliable way to know
what I am reading.
I set the read length to 2 bytes because most of the "atomic"reads are
two bytes and it allows us to test various commands directly from
userspace and read meaningful values. This is a limitation as:
* Voltage 'atomic' reads are 2 bytes
* Temperature 'atomic' reads are 2 bytes but never come alone (usually
one voltage input of 2B will follow).
* Any other 'condensed' input will be more than 2 bytes, ie. several
voltage values in one go.
In any case, doing a software reset of the chip will turn it back
into a working state no matter what was requested/read.
For me, 2-byte reads is a "good enough" solution that will work with
almost all the simplest ('atomic') SPI operations, but if you think
limiting to 2-bytes access is a problem (right now there is only write
access, which is kind of useless on its own) then let's drop the patch.
But I wanted to contribute it because it really helped me during the
development.
Thanks,
Miquèl
