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

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Message-ID: <87inb7c2ld.fsf@anholt.net>
Date:   Thu, 08 Feb 2018 08:22:54 +0000
From:   Eric Anholt <eric@...olt.net>
To:     "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,
        "Gustavo A. R. Silva" <garsilva@...eddedor.com>
Subject: Re: [PATCH] spi: bcm2835aux: use 64-bit arithmetic instead of 32-bit

"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>

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