RE: [PATCH RFC 3/5] Add KSZ8795 switch driver

[Tristram.Ha]

> > My concern is if a task is already running with SPI access to a lot
> > of registers like reading the 32 MIB counters in every port of the
> > switch, another register access has to wait until they are finished.
> 
> Why does it have to wait? Looking at the code in
> ksz_get_ethtool_stats(), you don't take any mutex which will prevent
> others from using the SPI bus. All there is is a mutex which prevents
> two sets of ksz_get_ethtool_stats() at the same time.
> 
> So a PTP read could happen in parallel, and will not be blocked by MIB
> reads. They should get interleaved access to the SPI bus.
> 

The MIB counters are read in the background.  For multiple CPU cores 2
tasks may run in the same time allowing SPI access one after another.
For single core I am not sure an SPI access like coming from an interrupt
routine can jump ahead from one in a background task.

I know nowadays SoCs are powerful enough to do amazing things.  It is
just I spent a long time using a low-powered SoC doing switch driver
development.