Re: [PATCH] net: stmmac: Change the busy-wait loops timing

[Andrew Lunn <andrew@lunn.ch>]

On Fri, Jun 06, 2025 at 12:19:49PM +0200, Bartlomiej Dziag wrote:
> After writing a new value to the PTP_TAR or PTP_STSUR registers,
> the driver waits for the addend/adjust operations to complete.
> Sometimes, the first check operation fails, resulting in
> a 10 milliseconds busy-loop before performing the next check.
> Since updating the registers takes much less than 10 milliseconds,
> the kernel gets stuck unnecessarily. This may increase the CPU usage.
> Fix that with changing the busy-loop interval to 5 microseconds.
> The registers will be checked more often.
> 
> Signed-off-by: Bartlomiej Dziag <bartlomiejdziag@gmail.com>
> ---
>  drivers/net/ethernet/stmicro/stmmac/stmmac_hwtstamp.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_hwtstamp.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_hwtstamp.c
> index e2840fa241f2..f8e1278a1837 100644
> --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_hwtstamp.c
> +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_hwtstamp.c
> @@ -144,11 +144,11 @@ static int config_addend(void __iomem *ioaddr, u32 addend)
>  	writel(value, ioaddr + PTP_TCR);
>  
>  	/* wait for present addend update to complete */
> -	limit = 10;
> +	limit = 10000;
>  	while (limit--) {
>  		if (!(readl(ioaddr + PTP_TCR) & PTP_TCR_TSADDREG))
>  			break;
> -		mdelay(10);
> +		udelay(5);

I would actually suggest rewriting this using the macros from iopoll.h.

    Andrew

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