Re: change r2pro dts to public hw version (was "Board code with 2 dts" )

[Trent Piepho <trent.piepho@igorinstitute.com>]

On Sat, Apr 9, 2022 at 9:02 AM Oleksij Rempel <linux@rempel-privat.de> wrote:>
>
> In this case driver will set some default values:
> priv->tx_delay = 0x30;
> priv->rx_delay = 0x10;
>
> No idea what this values mean.

They are supposed to be delays in picoseconds, but sometimes driver
authors are lazy and just use whatever goes into their device's
registers.  That creates a dts binding that only works for one
specific device.

> >> I would suggest to take an oscilloscope and measure rgmii clk and data lines. Make sure it is using
> >> correct frequency and the clock skew (delay between clk and data)
> >
> > have no oscilloscope here as i'm a private person and do this as hobby
>
> i have private oscilloscope, no idea what to answer :)

I also have a scope, but mine does not do picoseconds!  Those are expensive.

What you can do, is just write a test program that goes through every
delay value and measures how many packets it was able to send or
receive.  The success rate will probably look something like this:

0% 0% 5% 99% 100% 100% 100% 100% 99% 0% 0%

If the first value is for delay = 0 and they go up by 1 , then
probably delay = 5 or 6 is the best value to use.

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