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From: Jakub Kicinski <kuba@kernel.org>
To: David Laight <David.Laight@ACULAB.COM>
Cc: Andrew Lunn <andrew@lunn.ch>, netdev <netdev@vger.kernel.org>,
	Nicolas Pitre <nico@fluxnic.net>,
	"Lee Jones" <lee.jones@linaro.org>
Subject: Re: [PATCH net-next v2 1/7] drivers: net: smc91x: Fix set but unused W=1 warning
Date: Fri, 6 Nov 2020 09:42:13 -0800	[thread overview]
Message-ID: <20201106094213.62250632@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> (raw)
In-Reply-To: <749857e283f04d3b8f84f603fa065cd6@AcuMS.aculab.com>

On Fri, 6 Nov 2020 08:48:47 +0000 David Laight wrote:
> > > +#define SMC_GET_PKT_HDR_STATUS(lp, status)				\
> > > +	do {								\
> > > +		if (SMC_32BIT(lp)) {					\
> > > +			unsigned int __val = SMC_inl(ioaddr, DATA_REG(lp)); \
> > > +			(status) = __val & 0xffff;			\
> > > +		} else {						\
> > > +			(status) = SMC_inw(ioaddr, DATA_REG(lp));	\
> > > +		}							\
> > > +	} while (0)  
> > 
> > This is the original/full macro:
> > 
> > #define SMC_GET_PKT_HDR(lp, status, length)				\
> > 	do {								\
> > 		if (SMC_32BIT(lp)) {				\
> > 			unsigned int __val = SMC_inl(ioaddr, DATA_REG(lp)); \
> > 			(status) = __val & 0xffff;			\
> > 			(length) = __val >> 16;				\
> > 		} else {						\
> > 			(status) = SMC_inw(ioaddr, DATA_REG(lp));	\
> > 			(length) = SMC_inw(ioaddr, DATA_REG(lp));	\
> > 		}							\
> > 	} while (0)
> > 
> > Note that it reads the same address twice in the else branch.
> > 
> > I'm 90% sure we can't remove the read here either so best treat it
> > like the ones in patch 3, right?  
> 
> One of the two SMC_inw() needs to use 'ioaddr + 2'.
> Probably the one for (length).
> 
> The code may also be buggy on BE systems.

More proof that this code is fragile.

Changing IO accesses is not acceptable in a "warning cleanup" patch,
unless it can be tested on real HW.

We can follow up on the issues you see separately, please.

  reply	other threads:[~2020-11-06 17:42 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-11-04 15:48 [PATCH net-next v2 0/7] smsc W=1 warning fixes Andrew Lunn
2020-11-04 15:48 ` [PATCH net-next v2 1/7] drivers: net: smc91x: Fix set but unused W=1 warning Andrew Lunn
2020-11-05 22:37   ` Jakub Kicinski
2020-11-06  8:48     ` David Laight
2020-11-06 17:42       ` Jakub Kicinski [this message]
2020-11-04 15:48 ` [PATCH net-next v2 2/7] drivers: net: smc91x: Fix missing kerneldoc reported by W=1 Andrew Lunn
2020-11-04 15:48 ` [PATCH net-next v2 3/7] drivers: net: smc911x: Work around set but unused status Andrew Lunn
2020-11-04 15:48 ` [PATCH net-next v2 4/7] drivers: net: smc911x: Fix set but unused status because of DBG macro Andrew Lunn
2020-11-04 15:48 ` [PATCH net-next v2 5/7] drivers: net: smc911x: Fix passing wrong number of parameters to DBG() macro Andrew Lunn
2020-11-04 15:48 ` [PATCH net-next v2 6/7] drivers: net: smc911x: Fix cast from pointer to integer of different size Andrew Lunn
2020-11-05 22:47   ` Jakub Kicinski
2020-11-06  8:44     ` David Laight
2020-11-06 15:05       ` Nicolas Pitre
2020-11-06 15:29         ` David Laight
2020-11-06 15:47           ` Nicolas Pitre
2020-11-04 15:48 ` [PATCH net-next v2 7/7] drivers: net: smsc: Add COMPILE_TEST support Andrew Lunn

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