netdev - Re: [PATCH net-next] ptp: ocp: Improve PCIe delay estimation

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Message-ID: <20240904202035.GF1722938@kernel.org>
Date: Wed, 4 Sep 2024 21:20:35 +0100
From: Simon Horman <horms@...nel.org>
To: Vadim Fedorenko <vadim.fedorenko@...ux.dev>
Cc: Jakub Kicinski <kuba@...nel.org>,
	Jonathan Lemon <jonathan.lemon@...il.com>,
	Paolo Abeni <pabeni@...hat.com>, David Ahern <dsahern@...nel.org>,
	netdev@...r.kernel.org
Subject: Re: [PATCH net-next] ptp: ocp: Improve PCIe delay estimation

On Wed, Sep 04, 2024 at 01:28:42PM +0000, Vadim Fedorenko wrote:
> The PCIe bus can be pretty busy during boot and probe function can
> see excessive delays. Let's find the minimal value out of several
> tests and use it as estimated value.
> 
> Signed-off-by: Vadim Fedorenko <vadim.fedorenko@...ux.dev>
> ---
>  drivers/ptp/ptp_ocp.c | 17 ++++++++++-------
>  1 file changed, 10 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/ptp/ptp_ocp.c b/drivers/ptp/ptp_ocp.c
> index e7479b9b90cb..22b22e605781 100644
> --- a/drivers/ptp/ptp_ocp.c
> +++ b/drivers/ptp/ptp_ocp.c
> @@ -1561,19 +1561,22 @@ ptp_ocp_estimate_pci_timing(struct ptp_ocp *bp)
>  	ktime_t start, end;
>  	ktime_t delay;
>  	u32 ctrl;
> +	int i;
>  
> -	ctrl = ioread32(&bp->reg->ctrl);
> -	ctrl = OCP_CTRL_READ_TIME_REQ | OCP_CTRL_ENABLE;
> +	for (i = 0; i < 3; i++) {
> +		ctrl = ioread32(&bp->reg->ctrl);
> +		ctrl = OCP_CTRL_READ_TIME_REQ | OCP_CTRL_ENABLE;
>  
> -	iowrite32(ctrl, &bp->reg->ctrl);
> +		iowrite32(ctrl, &bp->reg->ctrl);
>  
> -	start = ktime_get_ns();
> +		start = ktime_get_ns();
>  
> -	ctrl = ioread32(&bp->reg->ctrl);
> +		ctrl = ioread32(&bp->reg->ctrl);
>  
> -	end = ktime_get_ns();
> +		end = ktime_get_ns();
>  
> -	delay = end - start;
> +		delay = min(delay, end - start);

Hi Vadim,

It looks like delay is used uninitialised here
in the first iteration of this loop.

Flagged by Smatch.

> +	}
>  	bp->ts_window_adjust = (delay >> 5) * 3;
>  }
>  
> -- 
> 2.43.0
> 
>