linux-kernel - Re: [PATCH net v2] net: stmmac: add clk_prepare

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Message-ID: <aRypZZ88K8tnh9Ha@shell.armlinux.org.uk>
Date: Tue, 18 Nov 2025 17:14:13 +0000
From: "Russell King (Oracle)" <linux@...linux.org.uk>
To: Paolo Abeni <pabeni@...hat.com>
Cc: Pavel Zhigulin <Pavel.Zhigulin@...persky.com>,
	Andrew Lunn <andrew+netdev@...n.ch>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Maxime Coquelin <mcoquelin.stm32@...il.com>,
	Alexandre Torgue <alexandre.torgue@...s.st.com>,
	Maxime Chevallier <maxime.chevallier@...tlin.com>,
	Inochi Amaoto <inochiama@...il.com>,
	Quentin Schulz <quentin.schulz@...rry.de>,
	Joe Hattori <joe@...is.s.u-tokyo.ac.jp>,
	Rayagond Kokatanur <rayagond@...avyalabs.com>,
	Giuseppe CAVALLARO <peppe.cavallaro@...com>, netdev@...r.kernel.org,
	linux-stm32@...md-mailman.stormreply.com,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	lvc-project@...uxtesting.org
Subject: Re: [PATCH net v2] net: stmmac: add clk_prepare_enable() error
 handling

On Tue, Nov 18, 2025 at 03:30:09PM +0100, Paolo Abeni wrote:
> On 11/14/25 3:23 PM, Pavel Zhigulin wrote:
> > The driver previously ignored the return value of 'clk_prepare_enable()'
> > for both the CSR clock and the PCLK in 'stmmac_probe_config_dt()' function.
> > 
> > Add 'clk_prepare_enable()' return value checks.
> > 
> > Found by Linux Verification Center (linuxtesting.org) with SVACE.
> > 
> > Fixes: bfab27a146ed ("stmmac: add the experimental PCI support")
> > Signed-off-by: Pavel Zhigulin <Pavel.Zhigulin@...persky.com>
> > ---
> > v2: Fix 'ret' value initialization after build bot notification.
> > v1: https://lore.kernel.org/all/20251113134009.79440-1-Pavel.Zhigulin@kaspersky.com/
> > 
> >  drivers/net/ethernet/stmicro/stmmac/stmmac_platform.c | 11 +++++++++--
> >  1 file changed, 9 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_platform.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_platform.c
> > index 27bcaae07a7f..8f9eb9683d2b 100644
> > --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_platform.c
> > +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_platform.c
> > @@ -632,7 +632,9 @@ stmmac_probe_config_dt(struct platform_device *pdev, u8 *mac)
> >  			dev_warn(&pdev->dev, "Cannot get CSR clock\n");
> >  			plat->stmmac_clk = NULL;
> >  		}
> > -		clk_prepare_enable(plat->stmmac_clk);
> > +		rc = clk_prepare_enable(plat->stmmac_clk);
> > +		if (rc < 0)
> > +			dev_warn(&pdev->dev, "Cannot enable CSR clock: %d\n", rc);
> >  	}
> > 
> >  	plat->pclk = devm_clk_get_optional(&pdev->dev, "pclk");
> > @@ -640,7 +642,12 @@ stmmac_probe_config_dt(struct platform_device *pdev, u8 *mac)
> >  		ret = plat->pclk;
> >  		goto error_pclk_get;
> >  	}
> > -	clk_prepare_enable(plat->pclk);
> > +	rc = clk_prepare_enable(plat->pclk);
> > +	if (rc < 0) {
> > +		ret = ERR_PTR(rc);
> > +		dev_err(&pdev->dev, "Cannot enable pclk: %d\n", rc);
> > +		goto error_pclk_get;
> > +	}
> 
> It looks like the driver is supposed to handle the
> IS_ERR_OR_NULL(plat->pclk) condition. This check could cause regression
> on existing setup currently failing to initialize the (optional) clock
> and still being functional.
> 
> I *think* we are better off without the added checks.

Note that the clk API permits NULL as valid. CCF checks for this
in clk_prepare() and avoids returning an error:

        if (!clk)
                return 0;

Same check in clk_enable(). So if plat->pclk is NULL, then no error
will be returned.

Places that set plat->pclk:

stmmac_probe_config_dt() - checks for error-pointers and fails. This
will cause driver probe failure.

dwc_qos_probe() - uses stmmac_pltfr_find_clk() which returns the
clk from the bulk-get or NULL. These clocks will have been obtained
using devm_clk_bulk_get_all_enabled(), which I think will return an
error if any fail, which fails the driver probe.

So, I don't think plat->pclk can be an error-pointer here.

Therefore, I don't think there's any concern with error pointers
or NULL in plat->pclk.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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