Subject: Re: [net-next v3 3/7] mv88e6xxx: reject unsupported external timestamp flags

From: Richard Cochran <[email-masked]>
Date: Sat, 12 Oct 2019 11:24:09 -0700

On Thu, Sep 26, 2019 at 11:11:05AM -0700, Jacob Keller wrote:
> Fix the mv88e6xxx PTP support to explicitly reject any future flags that
> get added to the external timestamp request ioctl.
> 
> In order to maintain currently functioning code, this patch accepts all
> three current flags. This is because the PTP_RISING_EDGE and
> PTP_FALLING_EDGE flags have unclear semantics

For the record, the semantics are (or should be):

  flags                                                 Meaning                   
  ----------------------------------------------------  -------------------------- 
  PTP_ENABLE_FEATURE                                    invalid                   
  PTP_ENABLE_FEATURE|PTP_RISING_EDGE                    Time stamp rising edge
  PTP_ENABLE_FEATURE|PTP_FALLING_EDGE                   Time stamp falling edge
  PTP_ENABLE_FEATURE|PTP_RISING_EDGE|PTP_FALLING_EDGE   Time stamp both edges   

> and each driver seems to
> have interpreted them slightly differently.

This driver has:

  flags                                                 Meaning                   
  ----------------------------------------------------  -------------------------- 
  PTP_ENABLE_FEATURE                                    Time stamp falling edge
  PTP_ENABLE_FEATURE|PTP_RISING_EDGE                    Time stamp rising edge
  PTP_ENABLE_FEATURE|PTP_FALLING_EDGE                   Time stamp falling edge
  PTP_ENABLE_FEATURE|PTP_RISING_EDGE|PTP_FALLING_EDGE   Time stamp rising edge
 
> Cc: Brandon Streiff <[email-masked]>
> Signed-off-by: Jacob Keller <[email-masked]>

Reviewed-by: Richard Cochran <[email-masked]>