linux-kernel - Re: [PATCH v4 16/16] net: stmmac: dwmac-s32: Read PTP clock rate when ready

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Message-ID: <ZzoOGdlbQXQVxPkv@lsv051416.swis.nl-cdc01.nxp.com>
Date: Sun, 17 Nov 2024 16:39:05 +0100
From: Jan Petrous <jan.petrous@....nxp.com>
To: Andrew Lunn <andrew@...n.ch>
Cc: Maxime Coquelin <mcoquelin.stm32@...il.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>,
	Vinod Koul <vkoul@...nel.org>,
	Richard Cochran <richardcochran@...il.com>,
	Heiner Kallweit <hkallweit1@...il.com>,
	Russell King <linux@...linux.org.uk>,
	Shawn Guo <shawnguo@...nel.org>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Pengutronix Kernel Team <kernel@...gutronix.de>,
	Fabio Estevam <festevam@...il.com>,
	Emil Renner Berthing <kernel@...il.dk>,
	Minda Chen <minda.chen@...rfivetech.com>,
	Nicolas Ferre <nicolas.ferre@...rochip.com>,
	Claudiu Beznea <claudiu.beznea@...on.dev>,
	Iyappan Subramanian <iyappan@...amperecomputing.com>,
	Keyur Chudgar <keyur@...amperecomputing.com>,
	Quan Nguyen <quan@...amperecomputing.com>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Giuseppe Cavallaro <peppe.cavallaro@...com>,
	linux-stm32@...md-mailman.stormreply.com,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org, linux-arm-msm@...r.kernel.org,
	imx@...ts.linux.dev, devicetree@...r.kernel.org,
	NXP S32 Linux Team <s32@....com>,
	Andrei Botila <andrei.botila@....org>,
	Jacob Keller <jacob.e.keller@...el.com>
Subject: Re: [PATCH v4 16/16] net: stmmac: dwmac-s32: Read PTP clock rate
 when ready

On Tue, Oct 29, 2024 at 01:18:43PM +0100, Andrew Lunn wrote:
> On Mon, Oct 28, 2024 at 09:24:58PM +0100, Jan Petrous via B4 Relay wrote:
> > From: "Jan Petrous (OSS)" <jan.petrous@....nxp.com>
> > 
> > The PTP clock is read by stmmac_platform during DT parse.
> > On S32G/R the clock is not ready and returns 0. Postpone
> > reading of the clock on PTP init.
> 
> This needs more explanation as to why this is a feature, not a bug,
> for the PTP clock.
> 

Thanks for comment. I did a homework and found out the root cause is
using PTP clocks before they are properly enabled. As I understand,
the clocks, especially the composite variant, require preparation and/or
enabling them, what is not managed correctly for PTP clocks when
stmmac_platform is used. In this case, the PTP clock value is read this way:

   stmmac_probe_config_dt:
   // https://github.com/torvalds/linux/blob/4a5df37964673effcd9f84041f7423206a5ae5f2/drivers/net/ethernet/stmicro/stmmac/stmmac_platform.c#L634

	/* Fall-back to main clock in case of no PTP ref is passed */
	plat->clk_ptp_ref = devm_clk_get(&pdev->dev, "ptp_ref");
	if (IS_ERR(plat->clk_ptp_ref)) {
		plat->clk_ptp_rate = clk_get_rate(plat->stmmac_clk);
		plat->clk_ptp_ref = NULL;
		dev_info(&pdev->dev, "PTP uses main clock\n");
	} else {
		plat->clk_ptp_rate = clk_get_rate(plat->clk_ptp_ref);
		dev_dbg(&pdev->dev, "PTP rate %d\n", plat->clk_ptp_rate);
	}

If I change getter to enabled getter:
	plat->clk_ptp_ref = devm_clk_get_enabled(&pdev->dev, "ptp_ref");

The driver got valid rate and the patch is not needed anymore.

So, if I didn't miss something, it seems like I have to replace the current
patch with one fixing clk getter.

BR.
/Jan