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

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Message-ID: <6e33c038-45a7-4941-b5d9-ce5704e13d48@lunn.ch>
Date: Tue, 16 Jan 2024 23:35:18 +0100
From: Andrew Lunn <andrew@...n.ch>
To: Bernd Edlinger <bernd.edlinger@...mail.de>
Cc: Alexandre Torgue <alexandre.torgue@...s.st.com>,
	Jose Abreu <joabreu@...opsys.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Maxime Coquelin <mcoquelin.stm32@...il.com>, netdev@...r.kernel.org,
	linux-stm32@...md-mailman.stormreply.com,
	linux-arm-kernel@...ts.infradead.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Jiri Pirko <jiri@...dia.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v2] net: stmmac: Wait a bit for the reset to take effect

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