> There is no documented mapping from the 32 possible values of the
> IO_IMPEDANCE_CTRL field to values in the range 35-70 ohms
There have been a few active TI engineers submitting patches to TI PHY
drivers. Please could you reach out to them and ask if they can
provide documentation.
Having magic values in DT is not the preferred why to use it. Ideally
you should store Ohms in the cell and convert to the register value.
Andrew
On 06/06/2022 23.58, Andrew Lunn wrote:
>> There is no documented mapping from the 32 possible values of the
>> IO_IMPEDANCE_CTRL field to values in the range 35-70 ohms
>
> There have been a few active TI engineers submitting patches to TI PHY
> drivers. Please could you reach out to them and ask if they can
> provide documentation.
>
> Having magic values in DT is not the preferred why to use it. Ideally
> you should store Ohms in the cell and convert to the register value.
We've already asked TI for more detailed information, but apparently the
data sheet already says all there is to know. I should have worded the
commit message differently. Something like
There is no fixed mapping from register values to values in the range
35-70 ohms; it varies from chip to chip, and even that target range is
approximate.
So AFAICS the only meaningful thing to store in an nvmem cell is an
appropriate (per-board) raw value of that field.
I would think this would be very similar to how various sensors have
nvmem cells defining calibration data.
Rasmus
On Tue, 7 Jun 2022 13:54:30 +0200 Rasmus Villemoes wrote:
> On 06/06/2022 23.58, Andrew Lunn wrote:
> >> There is no documented mapping from the 32 possible values of the
> >> IO_IMPEDANCE_CTRL field to values in the range 35-70 ohms
> >
> > There have been a few active TI engineers submitting patches to TI PHY
> > drivers. Please could you reach out to them and ask if they can
> > provide documentation.
> >
> > Having magic values in DT is not the preferred why to use it. Ideally
> > you should store Ohms in the cell and convert to the register value.
>
> We've already asked TI for more detailed information, but apparently the
> data sheet already says all there is to know. I should have worded the
> commit message differently. Something like
>
> There is no fixed mapping from register values to values in the range
> 35-70 ohms; it varies from chip to chip, and even that target range is
> approximate.
The series was waiting for Andrew to come back but it ended up getting
marked as Changes Requested in PW. Would you mind reposting with the
modification to the commit message?