Re: [PATCH] net: ethernet: cavium: use div64_u64() instead of do_div()

From: Christophe JAILLET
Date: Wed Feb 09 2022 - 14:12:54 EST


Le 09/02/2022 à 09:39, Qing Wang a écrit :
From: Wang Qing <wangqing@xxxxxxxx>

do_div() does a 64-by-32 division.
When the divisor is u64, do_div() truncates it to 32 bits, this means it
can test non-zero and be truncated to zero for division.

fix do_div.cocci warning:
do_div() does a 64-by-32 division, please consider using div64_u64 instead.

Signed-off-by: Wang Qing <wangqing@xxxxxxxx>
---
drivers/net/ethernet/cavium/liquidio/lio_main.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/cavium/liquidio/lio_main.c b/drivers/net/ethernet/cavium/liquidio/lio_main.c
index ba28aa4..8e07192
--- a/drivers/net/ethernet/cavium/liquidio/lio_main.c
+++ b/drivers/net/ethernet/cavium/liquidio/lio_main.c
@@ -1539,7 +1539,7 @@ static int liquidio_ptp_adjfreq(struct ptp_clock_info *ptp, s32 ppb)
* compute the delta in terms of coprocessor clocks.
*/
delta = (u64)ppb << 32;
- do_div(delta, oct->coproc_clock_rate);
+ div64_u64(delta, oct->coproc_clock_rate);
spin_lock_irqsave(&lio->ptp_lock, flags);
comp = lio_pci_readq(oct, CN6XXX_MIO_PTP_CLOCK_COMP);
@@ -1672,7 +1672,7 @@ static void liquidio_ptp_init(struct octeon_device *oct)
u64 clock_comp, cfg;
clock_comp = (u64)NSEC_PER_SEC << 32;
- do_div(clock_comp, oct->coproc_clock_rate);
+ div64_u64(clock_comp, oct->coproc_clock_rate);
lio_pci_writeq(oct, clock_comp, CN6XXX_MIO_PTP_CLOCK_COMP);
/* Enable */

I think that all your recent patches about such conversions are broken.

See [1] were it was already reported that do_div() and div64_u64() don't have the same calling convention.

Looks that div64_u64() and div64_ul() works the same way.


CJ

[1]: https://lore.kernel.org/linux-kernel/20211117112559.jix3hmx7uwqmuryg@xxxxxxxxxxxxxx/