netdev - Re: [PATCH] net: stmmac: Fix PTP ref clock for Tegra234

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Message-ID: <85e27a26-b115-49aa-8e23-963bff11f3f6@lunn.ch>
Date: Thu, 12 Jun 2025 14:10:06 +0200
From: Andrew Lunn <andrew@...n.ch>
To: Subbaraya Sundeep <sbhatta@...vell.com>
Cc: Jon Hunter <jonathanh@...dia.com>, 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>,
	Maxime Coquelin <mcoquelin.stm32@...il.com>,
	Alexandre Torgue <alexandre.torgue@...s.st.com>,
	netdev@...r.kernel.org, linux-stm32@...md-mailman.stormreply.com,
	linux-tegra@...r.kernel.org,
	Alexis Lothorrr <alexis.lothore@...tlin.com>
Subject: Re: [PATCH] net: stmmac: Fix PTP ref clock for Tegra234

On Thu, Jun 12, 2025 at 10:57:49AM +0000, Subbaraya Sundeep wrote:
> Hi,
> 
> On 2025-06-12 at 06:20:32, Jon Hunter (jonathanh@...dia.com) wrote:
> > Since commit 030ce919e114 ("net: stmmac: make sure that ptp_rate is not
> > 0 before configuring timestamping") was added the following error is
> > observed on Tegra234:
> > 
> >  ERR KERN tegra-mgbe 6800000.ethernet eth0: Invalid PTP clock rate
> >  WARNING KERN tegra-mgbe 6800000.ethernet eth0: PTP init failed
> > 
> > It turns out that the Tegra234 device-tree binding defines the PTP ref
> > clock name as 'ptp-ref' and not 'ptp_ref' and the above commit now
> > exposes this and that the PTP clock is not configured correctly.
> > 
> > Ideally, we would rename the PTP ref clock for Tegra234 to fix this but
> > this will break backward compatibility with existing device-tree blobs.
> > Therefore, fix this by using the name 'ptp-ref' for devices that are
> > compatible with 'nvidia,tegra234-mgbe'.

> AFAIU for Tegra234 device from the beginning, entry in dts is ptp-ref.
> Since driver is looking for ptp_ref it is getting 0 hence the crash
> and after the commit 030ce919e114 result is Invalid error instead of crash.
> For me PTP is not working for Tegra234 from day 1 so why to bother about
> backward compatibility and instead fix dts.
> Please help me understand it has been years I worked on dts.

Please could you expand on that, because when i look at the code....


  	/* 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;

if the ptp_ref does not exist, it falls back to stmmac_clk. Why would
that cause a crash?

While i agree if this never worked, we can ignore backwards
compatibility and just fix the DT, but i would like a fuller
explanation why the fallback is not sufficient to prevent a crash.

	Andrew