On Wed, 2018-02-07 at 10:00 -0600, Gustavo A. R. Silva 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
> Signed-off-by: Gustavo A. R. Silva <gust...@embeddedor.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 */
if (xfer_time_us < BCM2835_AUX_SPI_POLLING_LIMIT_US)
If one looks at the logic as a whole...
tfr->len * 9ULL * 100000 / spi_used_hz < 30
A little algebra can change that into:
tfr->len < spi_used_hz / 300000
So rather than add more 64-bit math, it can be removed entirely. Both
the length and speed are 32 bits and there's no need to multiply them
into something larger than might need 64 bits.
