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

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Message-ID: <ef733d84-3e44-49b9-a7ef-a8c4ff1eca65@linux.dev>
Date: Wed, 4 Sep 2024 23:42:48 +0100
From: Vadim Fedorenko <vadim.fedorenko@...ux.dev>
To: Simon Horman <horms@...nel.org>
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 04/09/2024 21:20, Simon Horman wrote:
> 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.

Oh, yes, you are right, Simon. I'll send v2 with INT_MAX init for delay.

Thanks!

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