linux-kernel - Re: [PATCH v2 0/3] Add the dwmac driver support for T-HEAD TH1520 SoC

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Message-ID: <ZvWqF9DU+6i9O1VB@x1>
Date: Thu, 26 Sep 2024 11:38:15 -0700
From: Drew Fustini <dfustini@...storrent.com>
To: Andrew Lunn <andrew@...n.ch>
Cc: "David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Alexandre Torgue <alexandre.torgue@...s.st.com>,
	Giuseppe Cavallaro <peppe.cavallaro@...com>,
	Jose Abreu <joabreu@...opsys.com>,
	Jisheng Zhang <jszhang@...nel.org>,
	Maxime Coquelin <mcoquelin.stm32@...il.com>,
	Emil Renner Berthing <emil.renner.berthing@...onical.com>,
	Drew Fustini <drew@...7.com>, Guo Ren <guoren@...nel.org>,
	Fu Wei <wefu@...hat.com>, Conor Dooley <conor@...nel.org>,
	Paul Walmsley <paul.walmsley@...ive.com>,
	Palmer Dabbelt <palmer@...belt.com>,
	Albert Ou <aou@...s.berkeley.edu>, netdev@...r.kernel.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-stm32@...md-mailman.stormreply.com,
	linux-arm-kernel@...ts.infradead.org,
	linux-riscv@...ts.infradead.org
Subject: Re: [PATCH v2 0/3] Add the dwmac driver support for T-HEAD TH1520 SoC

On Thu, Sep 26, 2024 at 08:23:12PM +0200, Andrew Lunn wrote:
> > Regarding rx and tx internal delays, that same section in the manual
> > doesn't specify what unit is represented by the delay_ctrl bit field in
> > GMAC_RXCLK_DELAY_CTRL and GMAC_TXCLK_DELAY_CTRL. It is only 5 bits and
> > a max value of 31 seems too small to represent picoseconds. The vendor
> > kernel [2] uses properties named "rx-clk-delay" and "tx-clk-delay" but
> > doesn't indicate any units. I see ti,dp83867.yaml adds vendor specific
> > rx and tx delay properties so that is what I've now done in this series.
> > Note: the hardware default value of 0 for delay_ctrl works okay for the
> > TH1520 hardware that I have.
> 
> I assume you are talking about RGMII delays here?
> 
> Do you have a board which needs to set these delays? In general, linux
> has the PHY provide the 2ns delay. You only need the MAC to add the
> delays if a PHY is being used which cannot add the needed
> delays. Occasionally you need to fine tune the delay, and the MAC
> delays can then be interesting. But since you have no idea what the
> units are, i would prefer to simply hard code it to 0, unless is it
> really needed.
> 
> 	Andrew

Yes, this is for the RGMII delays. None of the TH1520 boards that I have
seem to need this. The hardware reset value is 0 which seems to work
okay.

I'll remove these custom properties in the next revision.

Thanks,
Drew