netdev - Re: [PATCH net-next 3/3] net: stmmac: Add glue layer for Spacemit K3 SoC

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Message-ID: <aXACRN7BaumIySp3@inochi.infowork>
Date: Wed, 21 Jan 2026 06:36:01 +0800
From: Inochi Amaoto <inochiama@...il.com>
To: Andrew Lunn <andrew@...n.ch>, Inochi Amaoto <inochiama@...il.com>
Cc: Andrew Lunn <andrew+netdev@...n.ch>, 
	"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>, Yixun Lan <dlan@...too.org>, 
	Maxime Coquelin <mcoquelin.stm32@...il.com>, Alexandre Torgue <alexandre.torgue@...s.st.com>, 
	Richard Cochran <richardcochran@...il.com>, Paul Walmsley <pjw@...nel.org>, 
	Palmer Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>, 
	Alexandre Ghiti <alex@...ti.fr>, "Russell King (Oracle)" <rmk+kernel@...linux.org.uk>, 
	Yanteng Si <siyanteng@...oftware.com.cn>, Yao Zi <ziyao@...root.org>, 
	Vladimir Oltean <vladimir.oltean@....com>, Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>, 
	Choong Yong Liang <yong.liang.choong@...ux.intel.com>, Maxime Chevallier <maxime.chevallier@...tlin.com>, 
	Chen-Yu Tsai <wens@...nel.org>, Shangjuan Wei <weishangjuan@...incomputing.com>, 
	Boon Khai Ng <boon.khai.ng@...era.com>, Quentin Schulz <quentin.schulz@...rry.de>, 
	Giuseppe Cavallaro <peppe.cavallaro@...com>, Jose Abreu <joabreu@...opsys.com>, netdev@...r.kernel.org, 
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org, 
	spacemit@...ts.linux.dev, linux-stm32@...md-mailman.stormreply.com, 
	linux-arm-kernel@...ts.infradead.org, Longbin Li <looong.bin@...il.com>
Subject: Re: [PATCH net-next 3/3] net: stmmac: Add glue layer for Spacemit K3
 SoC

On Tue, Jan 20, 2026 at 02:56:26PM +0100, Andrew Lunn wrote:
> > +/* Note: the delay step value is at 0.1ps */
> > +static const unsigned int k3_delay_step_10x[4] = {
> > +	367, 493, 559, 685
> > +};
> 
> Am i reading it correctly that RGMII delays are limited to these four
> values?
> 
> If so, please add this list to the DT binding.
> 

No, these value are just adjustment interval, and it is also
controlled by another code register, the final delay is calculated
by the following formula:

delay = delay_step * delay_code * 0.9;

So the delay configuration needs to be calculated instead of
directly assigned.

> > +static int spacemit_dwmac_detected_delay_value(unsigned int delay,
> > +					       unsigned int *config)
> > +{
> > +	int i;
> > +	int code, best_code = 0;
> > +	unsigned int best_delay = 0;
> > +	unsigned int best_config = 0;
> > +
> > +	if (delay == 0)
> > +		return 0;
> > +
> > +	for (i = 0; i < ARRAY_SIZE(k3_delay_step_10x); i++) {
> > +		unsigned int step = k3_delay_step_10x[i];
> > +
> > +		for (code = 1; code <= MAX_DLINE_DELAY_CODE; code++) {
> > +			/*
> > +			 * Note K3 require a specific factor for calculate
> > +			 * the delay, in this scenario it is 0.9. So the
> > +			 * formula is code * step / 10 * 0.9
> > +			 */
> > +			unsigned int tmp = code * step * 9 / 10 / 10;
> > +
> > +			if (abs(tmp - delay) < abs(best_delay - delay)) {
> > +				best_code = code;
> > +				best_delay = tmp;
> > +				best_config = i;
> > +			}
> > +		}
> > +	}
> 
> With the four values listed in DT, i would make this a straight match,
> not the nearest, and return -EINVAL otherwise.
> 
>     Andrew

Regards,
Inochi