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

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Date:   Thu, 8 Feb 2018 09:54:38 +0000
From:   Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:     "Gustavo A. R. Silva" <gustavo@...eddedor.com>
Cc:     Mark Brown <broonie@...nel.org>, Eric Anholt <eric@...olt.net>,
        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,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "Gustavo A. R. Silva" <garsilva@...eddedor.com>,
        linux-rpi-kernel@...ts.infradead.org,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-spi@...r.kernel.org
Subject: Re: [PATCH] spi: bcm2835aux: use 64-bit arithmetic instead of 32-bit

On 7 February 2018 at 16:00, Gustavo A. R. Silva <gustavo@...eddedor.com> wrote:
> 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

What does this number mean? If it is an index into some internal
database, please remove it.

> Signed-off-by: Gustavo A. R. Silva <gustavo@...eddedor.com>
> ---
>  drivers/spi/spi-bcm2835aux.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/spi/spi-bcm2835aux.c b/drivers/spi/spi-bcm2835aux.c
> index 7428091..a768c23 100644
> --- a/drivers/spi/spi-bcm2835aux.c
> +++ b/drivers/spi/spi-bcm2835aux.c
> @@ -363,7 +363,7 @@ static int bcm2835aux_spi_transfer_one(struct spi_master *master,
>          * chunk getting transferred - in our case the chunk size
>          * is 3 bytes, so we approximate this by 9 bits/byte
>          */
> -       xfer_time_us = tfr->len * 9 * 1000000;
> +       xfer_time_us = tfr->len * 9ULL * 1000000;
>         do_div(xfer_time_us, spi_used_hz);
>
>         /* run in polling mode for short transfers */
> --
> 2.7.4
>
>
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

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