linux-kernel - Re: coccinelle and bitmask arithmetic

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Date:	Wed, 30 Jan 2013 09:21:28 +0100
From:	walter harms <wharms@....de>
To:	Joe Perches <joe@...ches.com>
CC:	Julia Lawall <julia.lawall@...6.fr>,
	Russell King <linux@....linux.org.uk>,
	Mike Rapoport <mike@...pulab.co.il>, Valdis.Kletnieks@...edu,
	cocci@...teme.lip6.fr, Dan Carpenter <dan.carpenter@...cle.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jslaby@...e.cz>,
	Paul Fulghum <paulkf@...rogate.com>,
	David Howells <dhowells@...hat.com>,
	linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: Re: coccinelle and bitmask arithmetic



Am 29.01.2013 19:03, schrieb Joe Perches:
> On Tue, 2013-01-29 at 18:49 +0100, Julia Lawall wrote:
>> How about the following (from today's linux-next).  They appear to be
>> trying to do the same calculation, once with + and once with |.
> 
> (cc'ing the original developer and Russell King)
> 
> Likely the it8152_pci_platform_notify uses should use +
> 
>> arch/arm/common/it8152.c
>>
>> int dma_set_coherent_mask(struct device *dev, u64 mask)
>> {
>>         if (mask >= PHYS_OFFSET + SZ_64M - 1)
>>                 return 0;
>>
>>         return -EIO;
>> }
>>

Great hit Joe :)

Sometimes i am really surprised what code can be found
in the kernal and it is still working.
Having no clue of the code i suspect somebody tries to
check is mask outside the range it should read
PHYS_OFFSET |( SZ_64M - 1)
maybe someone should tell them that
1+1=10 while 1|1=1
It does not seem to matter here (or ... ?)

really perplexed,

wh


>> static int it8152_pci_platform_notify(struct device *dev)
>> {
>>         if (dev->bus == &pci_bus_type) {
>>                 if (dev->dma_mask)
>>                         *dev->dma_mask = (SZ_64M - 1) | PHYS_OFFSET;
>>                 dev->coherent_dma_mask = (SZ_64M - 1) | PHYS_OFFSET;
>>                 dmabounce_register_dev(dev, 2048, 4096, it8152_needs_bounce);
>>         }
>>         return 0;
>> }
> 
> 
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