netdev - Re: [PATCH v2] net: stmmac: correct MAC propagation delay

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Date: Thu, 27 Jul 2023 09:20:10 +0200
From: Johannes Zink <j.zink@...gutronix.de>
To: Richard Cochran <richardcochran@...il.com>
Cc: Giuseppe Cavallaro <peppe.cavallaro@...com>,
 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>, Russell King <linux@...linux.org.uk>,
 patchwork-jzi@...gutronix.de, netdev@...r.kernel.org,
 linux-stm32@...md-mailman.stormreply.com,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
 kernel@...gutronix.de, kernel test robot <lkp@...el.com>
Subject: Re: [PATCH v2] net: stmmac: correct MAC propagation delay

Hi Richard,

On 7/26/23 22:57, Richard Cochran wrote:
> On Mon, Jul 24, 2023 at 12:01:31PM +0200, Johannes Zink wrote:
> 
> Earlier versions of the IP core return zero from these...
> 
>> +#define	PTP_TS_INGR_LAT	0x68	/* MAC internal Ingress Latency */
>> +#define	PTP_TS_EGR_LAT	0x6c	/* MAC internal Egress Latency */
> 

good catch. Gonna send a v3 with a check to and set the values for dwmac v5 only.

Best regards
Johannes

> and so...
> 
>> +static void correct_latency(struct stmmac_priv *priv)
>> +{
>> +	void __iomem *ioaddr = priv->ptpaddr;
>> +	u32 reg_tsic, reg_tsicsns;
>> +	u32 reg_tsec, reg_tsecsns;
>> +	u64 scaled_ns;
>> +	u32 val;
>> +
>> +	/* MAC-internal ingress latency */
>> +	scaled_ns = readl(ioaddr + PTP_TS_INGR_LAT);
>> +
>> +	/* See section 11.7.2.5.3.1 "Ingress Correction" on page 4001 of
>> +	 * i.MX8MP Applications Processor Reference Manual Rev. 1, 06/2021
>> +	 */
>> +	val = readl(ioaddr + PTP_TCR);
>> +	if (val & PTP_TCR_TSCTRLSSR)
>> +		/* nanoseconds field is in decimal format with granularity of 1ns/bit */
>> +		scaled_ns = ((u64)NSEC_PER_SEC << 16) - scaled_ns;
>> +	else
>> +		/* nanoseconds field is in binary format with granularity of ~0.466ns/bit */
>> +		scaled_ns = ((1ULL << 31) << 16) -
>> +			DIV_U64_ROUND_CLOSEST(scaled_ns * PSEC_PER_NSEC, 466U);
>> +
>> +	reg_tsic = scaled_ns >> 16;
>> +	reg_tsicsns = scaled_ns & 0xff00;
>> +
>> +	/* set bit 31 for 2's compliment */
>> +	reg_tsic |= BIT(31);
>> +
>> +	writel(reg_tsic, ioaddr + PTP_TS_INGR_CORR_NS);
> 
> here reg_tsic = 0x80000000 for a correction of -2.15 seconds! >
> @Jakub  Can you please revert this patch?
> 
> Thanks,
> Richard
> 
> 

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