linux-kernel - Re: [PATCH v2] arm64: dts: rockchip: support Ethernet Switch adapter for RK3588 Jaguar

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Message-Id: <20250527131142.1100673-1-jakob.unterwurzacher@cherry.de>
Date: Tue, 27 May 2025 15:11:42 +0200
From: Jakob Unterwurzacher <jakobunt@...il.com>
To: foss+kernel@...il.net
Cc: conor+dt@...nel.org,
	devicetree@...r.kernel.org,
	heiko@...ech.de,
	jakob.unterwurzacher@...rry.de,
	krzk+dt@...nel.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	linux-rockchip@...ts.infradead.org,
	quentin.schulz@...rry.de,
	robh@...nel.org
Subject: Re: [PATCH v2] arm64: dts: rockchip: support Ethernet Switch adapter for RK3588 Jaguar

> @Jakob, is this something you could check? devmem2 0xfd58c31c w 0x3c0000
> should do the trick to disable the circuitry according to the TRM?

I measured TXCLK vs TXD3 on an oscilloscope on gmac1:

	Setting	Decimal	Actual TXCLK delay (ps)
	00	0	47
	0a	10	283
	10	16	440
	20	32	893
	30	48	1385
	40	64	1913
	50	80	2514
	60	96	3077
	70	112	3565
	7f	127	4009

	off	x	-315

Setting = tx_delay (hex)
Decimal = tx_delay (dec)
Actual TXCLK delay (ps) = Measurement from oscilloscope

Plotting this we can deduce that one tx_delay unit is about 31ps.

We can also see that turning off the delay unit does not give us zero
delay, but setting tx_delay to zero does (almost).

I did this on the Rockchip 6.1 kernel because it allows to set the
delays on runtime via sysfs
( https://gitlab.com/firefly-linux/docs/-/blob/rk356x/firefly/Common/GMAC/Rockchip_Developer_Guide_Linux_GMAC_RGMII_Delayline_EN.pdf )
but I don't expect it to make a difference.

Regards,
Jakob