netdev - Re: [PATCH net] ptp: ocp: have adjtime handle negative delta

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Message-ID: <0d054105-0142-ccf2-4d2d-43767f63ca46@novek.ru>
Date:   Mon, 9 May 2022 02:22:36 +0100
From:   Vadim Fedorenko <vfedorenko@...ek.ru>
To:     Jonathan Lemon <jonathan.lemon@...il.com>
Cc:     netdev@...r.kernel.org, richardcochran@...il.com,
        kernel-team@...com, davem@...emloft.net, kuba@...nel.org,
        pabeni@...hat.com
Subject: Re: [PATCH net] ptp: ocp: have adjtime handle negative delta_ns
 correctly

On 08.05.2022 05:55, Jonathan Lemon wrote:
> On Sat, May 07, 2022 at 01:19:54AM +0100, Vadim Fedorenko wrote:
>> On 06.05.2022 00:40, Jonathan Lemon wrote:
>>> delta_ns is a s64, but it was being passed ptp_ocp_adjtime_coarse
>>> as an u64.  Also, it turns out that timespec64_add_ns() only handles
>>> positive values, so the math needs to be updated.
>>>
>>> Fix by passing in the correct signed value, then adding to a
>>> nanosecond version of the timespec.
>>>
>>> Fixes: '90f8f4c0e3ce ("ptp: ocp: Add ptp_ocp_adjtime_coarse for large adjustments")'
>>> Signed-off-by: Jonathan Lemon <jonathan.lemon@...il.com>
>>> ---
>>>    drivers/ptp/ptp_ocp.c | 6 ++++--
>>>    1 file changed, 4 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/ptp/ptp_ocp.c b/drivers/ptp/ptp_ocp.c
>>> index dd45471f6780..65e592ec272e 100644
>>> --- a/drivers/ptp/ptp_ocp.c
>>> +++ b/drivers/ptp/ptp_ocp.c
>>> @@ -841,16 +841,18 @@ __ptp_ocp_adjtime_locked(struct ptp_ocp *bp, u32 adj_val)
>>>    }
>>>    static void
>>> -ptp_ocp_adjtime_coarse(struct ptp_ocp *bp, u64 delta_ns)
>>> +ptp_ocp_adjtime_coarse(struct ptp_ocp *bp, s64 delta_ns)
>>>    {
>>>    	struct timespec64 ts;
>>>    	unsigned long flags;
>>>    	int err;
>>> +	s64 ns;
>>>    	spin_lock_irqsave(&bp->lock, flags);
>>>    	err = __ptp_ocp_gettime_locked(bp, &ts, NULL);
>>>    	if (likely(!err)) {
>>> -		timespec64_add_ns(&ts, delta_ns);
>>> +		ns = timespec64_to_ns(&ts) + delta_ns;
>>> +		ts = ns_to_timespec64(ns);
>>
>> Maybe use set_normalized_timespec64 instead of this ugly transformations and
>> additional variable?
> 
> I don't see how that would work - set_normalized_timespec64 just sets
> the ts from a <sec>.<nsec> value.  In this case, delta_ns need to be
> added in to the ts value, but timespec64_add_ns() doeesn't handle
> negative values, hence the conversion / add / reconversion.

Could be like:

-	timespec64_add_ns(&ts, delta_ns);
+	set_normalized_timespec64(&ts, ts.tv_sec, ts.tv_nsec + delta_ns);

That's actually without multiplication and division caused by two conversions.