Re: [PATCH v4 net-next 5/5] drivers/net/phy: add driver for the onsemi NCN26000 10BASE-T1S PHY

On Tue, Dec 06, 2022 at 08:12:02PM +0100, Andrew Lunn wrote:

quoted

I was wondering if there is some interface (sysfs / proc / other) to set
parameters which are very specific to a PHY implementation?

Please describe what they are, and in what context you need them. Then
we can decide on the correct API.

In general, the OS is there to abstract over the hardware so they all
look the same. We don't want anything specific to the PHY.

That's clear, let me explain.

Enable of enhanced-noise-immunity mode
- This trades off CSMA/CD performance for noise immunity. It could be a
  static setting, but the user may want to conditionally enable it
  depending on application decisions. E.g. some people may want to
  enable/disable this when using CSMA/CD as a fallback in case the PLCA
  coordinator disappears. Of course, there are better ways of doing
  this, but it is a possible use-case that some people want to use.

Tuning of internal impedance to match the line/MDI
- This is really board dependent, so DT seems good to me

Tuning of PMA filters to optimize SNR
- same as above?

Tuning of TX voltage levels
- I am not 100% sure that is static (DT) but for the time being it could
  be considered as such. It basically trades-off EMI (immunity) for EME
  (emissions).

Topology Discovery
- This is a special mode to detect the physical distance among nodes on
  the multi-drop cable. It is also being standardized in the OPEN
  Alliance, but for the time being, it is proprietary. I think it will
  require some kernel support as a protocol is also involved (but not
  standardized, yet).

Multi-putrpose I/Os (LED, GPIO, SFD detect).
- I know the kernel already has the infrastructure for those functions
  (not sure about SFD) so I assume this could be some DT work and some
  code to configure the MUX to achieve the specific function.

Selection of link status triggers
- This is what I was trying to achieve with the module parameter. i.e.,
  the link status can be a simple on/off based on the link_control
  setting (this is what it is for CSMA/CD as there is no link concept)
  or it could be masked by PLCA status whrn PLCA is enabled. This is a
  design choice of the user. In the former case, you don't get a link
  down if the PHY automatically go back to CSMA/CD as a result of PLCA
  status being 0. In the latter case you get a link down until PLCA is
  up & running, preventing the application to send data before time.

Thanks,
Piergiorgio