RE: [PATCH -next] ethernet: renesas: Use div64_ul instead of do_div

From: Sergey Shtylyov

Sent: 18 November 2021 09:08
On 18.11.2021 5:50, Yang Li wrote:

quoted

do_div() does a 64-by-32 division. Here the divisor is an
unsigned long which on some platforms is 64 bit wide. So use
div64_ul instead of do_div to avoid a possible truncation.

Eliminate the following coccicheck warning:
./drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c:2742:1-7: WARNING:
do_div() does a 64-by-32 division, please consider using div64_ul
instead.

Reported-by: Abaci Robot <redacted>
Signed-off-by: Yang Li <redacted>
---
  drivers/net/ethernet/renesas/ravb_main.c | 2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/renesas/ravb_main.c b/drivers/net/ethernet/renesas/ravb_main.c
index b4c597f..2b89710 100644
--- a/drivers/net/ethernet/renesas/ravb_main.c
+++ b/drivers/net/ethernet/renesas/ravb_main.c

@@ -2489,7 +2489,7 @@ static int ravb_set_gti(struct net_device *ndev)
  		return -EINVAL;

  	inc = 1000000000ULL << 20;
-	do_div(inc, rate);
+	inc = div64_ul(inc, rate);

    Why not just:

	inc = div64_ul(1000000000ULL << 20, rate);

quoted

  	if (inc < GTI_TIV_MIN || inc > GTI_TIV_MAX) {
  		dev_err(dev, "gti.tiv increment 0x%llx is outside the range 0x%x - 0x%x\n",

Even with hardware divide a 64/32 divide is likely to be faster that a 64/64 one.

Maybe the coccicheck warning message should suggest checking the domain
of the divisor and then changing the type??

	David

-
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