* Re: [PATCH -next] net: mvpp2: Use div64_ul instead of do_div
2021-11-18 3:05 [PATCH -next] net: mvpp2: Use div64_ul instead of do_div Yang Li
@ 2021-11-18 4:00 ` Eric Dumazet
0 siblings, 0 replies; 2+ messages in thread
From: Eric Dumazet @ 2021-11-18 4:00 UTC (permalink / raw)
To: Yang Li, davem
Cc: kuba, mw, linux, ast, daniel, hawk, john.fastabend, andrii,
kafai, songliubraving, yhs, kpsingh, netdev, linux-kernel, bpf
On 11/17/21 7:05 PM, Yang Li wrote:
> 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 <abaci@linux.alibaba.com>
> Signed-off-by: Yang Li <yang.lee@linux.alibaba.com>
> ---
> drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c b/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c
> index df6c793..41244a5 100644
> --- a/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c
> +++ b/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c
> @@ -2739,7 +2739,7 @@ static u32 mvpp2_cycles_to_usec(u32 cycles, unsigned long clk_hz)
> {
> u64 tmp = (u64)cycles * USEC_PER_SEC;
>
> - do_div(tmp, clk_hz);
> + tmp = div64_ul(tmp, clk_hz);
>
> return tmp > U32_MAX ? U32_MAX : tmp;
> }
>
This is silly, clk_hz fits in a u32, why pretends it is 64bit ?
diff --git a/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c b/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c
index df6c793f4b1b04eb1f812ce2a3a82a39cde0f68b..1bea316bf13ac42ad65ba326fc1d9e206546766e 100644
--- a/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c
+++ b/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c
@@ -2726,7 +2726,7 @@ static void mvpp2_tx_pkts_coal_set(struct mvpp2_port *port,
}
}
-static u32 mvpp2_usec_to_cycles(u32 usec, unsigned long clk_hz)
+static u32 mvpp2_usec_to_cycles(u32 usec, u32 clk_hz)
{
u64 tmp = (u64)clk_hz * usec;
@@ -2735,7 +2735,7 @@ static u32 mvpp2_usec_to_cycles(u32 usec, unsigned long clk_hz)
return tmp > U32_MAX ? U32_MAX : tmp;
}
-static u32 mvpp2_cycles_to_usec(u32 cycles, unsigned long clk_hz)
+static u32 mvpp2_cycles_to_usec(u32 cycles, u32 clk_hz)
{
u64 tmp = (u64)cycles * USEC_PER_SEC;
@@ -2748,7 +2748,7 @@ static u32 mvpp2_cycles_to_usec(u32 cycles, unsigned long clk_hz)
static void mvpp2_rx_time_coal_set(struct mvpp2_port *port,
struct mvpp2_rx_queue *rxq)
{
- unsigned long freq = port->priv->tclk;
+ u32 freq = port->priv->tclk;
u32 val = mvpp2_usec_to_cycles(rxq->time_coal, freq);
if (val > MVPP2_MAX_ISR_RX_THRESHOLD) {
@@ -2764,7 +2764,7 @@ static void mvpp2_rx_time_coal_set(struct mvpp2_port *port,
static void mvpp2_tx_time_coal_set(struct mvpp2_port *port)
{
- unsigned long freq = port->priv->tclk;
+ u32 freq = port->priv->tclk;
u32 val = mvpp2_usec_to_cycles(port->tx_time_coal, freq);
if (val > MVPP2_MAX_ISR_TX_THRESHOLD) {
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