linux-kernel - Re: [PATCH v2 3/6] EDAC/fsl_ddr: Fix bad bit shift operations

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Message-ID: <20241015161139.GEZw6UO2txZVBXffKc@fat_crate.local>
Date: Tue, 15 Oct 2024 18:11:39 +0200
From: Borislav Petkov <bp@...en8.de>
To: Frank Li <Frank.li@....com>
Cc: York Sun <york.sun@....com>, Tony Luck <tony.luck@...el.com>,
	James Morse <james.morse@....com>,
	Mauro Carvalho Chehab <mchehab@...nel.org>,
	Robert Richter <rric@...nel.org>,
	Krzysztof Kozlowski <krzk@...nel.org>,
	Rob Herring <robh@...nel.org>, Conor Dooley <conor+dt@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Shawn Guo <shawnguo@...nel.org>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Pengutronix Kernel Team <kernel@...gutronix.de>,
	Fabio Estevam <festevam@...il.com>, linux-edac@...r.kernel.org,
	linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
	imx@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org,
	Priyanka Singh <priyanka.singh@....com>,
	Sherry Sun <sherry.sun@....com>, Li Yang <leoyang.li@....com>
Subject: Re: [PATCH v2 3/6] EDAC/fsl_ddr: Fix bad bit shift operations

On Tue, Oct 15, 2024 at 11:31:41AM -0400, Frank Li wrote:
> I don't think it is urgent. In most system the return value is 0. I am not
> sure who caught it because patch already exist at downstream tree for a
> whole.

That current patch looks like it needs rethinking and making it sane - see
below.

> > > diff --git a/drivers/edac/fsl_ddr_edac.c b/drivers/edac/fsl_ddr_edac.c
> > > index 7a9fb1202f1a0..ccc13c2adfd6f 100644
> > > --- a/drivers/edac/fsl_ddr_edac.c
> > > +++ b/drivers/edac/fsl_ddr_edac.c
> > > @@ -338,11 +338,18 @@ static void fsl_mc_check(struct mem_ctl_info *mci)
> > >  			fsl_mc_printk(mci, KERN_ERR,
> > >  				"Faulty ECC bit: %d\n", bad_ecc_bit);
> > >
> > > -		fsl_mc_printk(mci, KERN_ERR,
> > > -			"Expected Data / ECC:\t%#8.8x_%08x / %#2.2x\n",
> > > -			cap_high ^ (1 << (bad_data_bit - 32)),
> > > -			cap_low ^ (1 << bad_data_bit),
> > > -			syndrome ^ (1 << bad_ecc_bit));
> > > +		if ((bad_data_bit > 0 && bad_data_bit < 32) && bad_ecc_bit > 0) {
> > > +			fsl_mc_printk(mci, KERN_ERR,
> > > +				      "Expected Data / ECC:\t%#8.8x_%08x / %#2.2x\n",
> > > +				      cap_high, cap_low ^ (1 << bad_data_bit),
> > > +				      syndrome ^ (1 << bad_ecc_bit));
> > > +		}
> > > +		if (bad_data_bit >= 32 && bad_ecc_bit > 0) {
> > > +			fsl_mc_printk(mci, KERN_ERR,
> > > +				      "Expected Data / ECC:\t%#8.8x_%08x / %#2.2x\n",
> > > +				      cap_high ^ (1 << (bad_data_bit - 32)),
> > > +				      cap_low, syndrome ^ (1 << bad_ecc_bit));
> > > +		}
> >
> > This is getting unnecessarily clumsy than it should be. Please do the
> > following:
> >
> > 	if (bad_data_bit != 1 && bad_ecc_bit != -1) {
> >
> > 		// prep the values you need to print
> >
> > 		// do an exactly one fsl_mc_printk() with the prepared values.
> >
> > 	}
> >
> > Not have 4 fsl_mc_printks with a bunch of silly if-checks in front.

You missed the most important feedback. See above. ^^^^^^^

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette