Re: [PATCH v2] net: stmmac: Wait a bit for the reset to take effect

[Andrew Lunn]

On Mon, Jan 15, 2024 at 08:21:42PM +0100, Bernd Edlinger wrote:
> otherwise the synopsys_id value may be read out wrong,
> because the GMAC_VERSION register might still be in reset
> state, for at least 1 us after the reset is de-asserted.
> 
> Add a wait for 10 us before continuing to be on the safe side.
> 
> > From what have you got that delay value?
> 
> Just try and error, with very old linux versions and old gcc versions
> the synopsys_id was read out correctly most of the time (but not always),
> with recent linux versions and recnet gcc versions it was read out
> wrongly most of the time, but again not always.
> I don't have access to the VHDL code in question, so I cannot
> tell why it takes so long to get the correct values, I also do not
> have more than a few hardware samples, so I cannot tell how long
> this timeout must be in worst case.
> Experimentally I can tell that the register is read several times
> as zero immediately after the reset is de-asserted

Is zero a valid synopsys_id? If its not, maybe do the wait conditional
on the first read returning 0?

   Andrew