linux-kernel - Re: [PATCH] spi: bcm2835aux: use 64-bit arithmetic instead of 32-bit

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Date:   Mon, 12 Feb 2018 11:57:20 -0600
From:   "Gustavo A. R. Silva" <garsilva@...eddedor.com>
To:     Eric Anholt <eric@...olt.net>,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        Mark Brown <broonie@...nel.org>,
        Stefan Wahren <stefan.wahren@...e.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Ray Jui <rjui@...adcom.com>,
        Scott Branden <sbranden@...adcom.com>,
        bcm-kernel-feedback-list@...adcom.com
Cc:     linux-spi@...r.kernel.org, linux-rpi-kernel@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] spi: bcm2835aux: use 64-bit arithmetic instead of 32-bit

Hi Eric,

On 02/08/2018 02:22 AM, Eric Anholt wrote:
> "Gustavo A. R. Silva" <gustavo@...eddedor.com> writes:
> 
>> Add suffix ULL to constant 9 in order to give the compiler complete
>> information about the proper arithmetic to use. Notice that this
>> constant is used in a context that expects an expression of type
>> unsigned long long (64 bits, unsigned).
>>
>> The expression tfr->len * 9 * 1000000 is currently being evaluated
>> using 32-bit arithmetic.
>>
>> Addresses-Coverity-ID: 1339619
>> Signed-off-by: Gustavo A. R. Silva <gustavo@...eddedor.com>
> 
> The effect looks like it would be that we would have chosen polling mode
> instead of waiting for interrupts for some transfers >477 seconds.
> Seems like a good fix for an unlikely bug.
> 
> Reviewed-by: Eric Anholt <eric@...olt.net>
> 

Thank you for your review.

--
Gustavo