netdev - Re: [PATCH RFC] mlx4_en: Add PTP hardware clock

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Date:	Thu, 12 Dec 2013 11:50:07 +0200
From:	Hadar Hen Zion <hadarh@...lanox.com>
To:	Shawn Bohrer <shawn.bohrer@...il.com>
CC:	Richard Cochran <richardcochran@...il.com>,
	Or Gerlitz <ogerlitz@...lanox.com>,
	Amir Vadai <amirv@...lanox.com>, <netdev@...r.kernel.org>,
	<tomk@...advisors.com>, Shawn Bohrer <sbohrer@...advisors.com>
Subject: Re: [PATCH RFC] mlx4_en: Add PTP hardware clock

On 12/11/2013 11:28 PM, Shawn Bohrer wrote:
> On Wed, Dec 11, 2013 at 07:54:39PM +0100, Richard Cochran wrote:
>> On Wed, Dec 11, 2013 at 12:24:25PM -0600, Shawn Bohrer wrote:
>>> From: Shawn Bohrer <sbohrer@...advisors.com>
>>>
>>> This adds a PHC to the mlx4_en driver.  This is largely based off of the
>>> e1000e driver (drivers/net/ethernet/intel/e1000e/ptp.c) which seemed
>>> very similar.  One thing I am unsure about is that in the e1000e driver
>>> they protect the timecounter code with a spinlock because the hardware
>>> reports the time in two 32bit registers.  The Mellanox code looks
>>> similar however the existing timecounter code in the mlx4_en driver
>>> wasn't protected with a lock so I left the lock out here as well.
>>
>> Before, there were only three call sites,
>>
>> grep -nH -e timecounter_ *
>> en_clock.c:108:	nsec = timecounter_cyc2time(&mdev->clock, timestamp);
>> en_clock.c:131:	timecounter_init(&mdev->clock, &mdev->cycles,
>> en_clock.c:148:		timecounter_read(&mdev->clock);
>>
>> and so perhaps the locking was unnecessary (but maybe not).
>> In any case, the code that you added definitely needs locks.
>>
>
> Yeah, that looked sketchy to me.  I've added the locks.
>
>>> Additionally here the mlx4_en_phc_adjfreq() method simply returns
>>> -EOPNOTSUPP because I don't have the relevant hardware documentation on
>>> how to do this.  I'm hoping one of the Mellanox developers can either
>>> provide this documentation or provide a patch to implement that
>>> function.
>>
>> Since the code already uses timecounter_read to convert clock ticks
>> into nanoseconds, why not simply adjust the 'mult' as other drivers
>> do?
>>
>> [ If the clock is easily adjustable in hardware, then, by all means,
>>    do it that way. ]
>
> Awesome, I totally missed this.  I've updated my code to do this for
> now and if there is a better way the Mellanox guys can chime in.
>
>>
>>> This is minimally tested at this point but Documentation/ptp/testptp
>>> appears to work on a Mellanox ConnectX-3 card.
>>
>> Once you have the adjustment in place, then you can try it with
>> linuxptp.
>
> Yep, that is the goal of this exercise.  I should have a v2 patch with
> these changes after I do some more testing.
>
> Thanks,
> Shawn
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Hi Shawn,

I'm a SW developer working in Mellanox SW team which is responsible for 
upstream related tasks.
I already had this task assigned to me and I was planning to start 
working on it soon. Anyway now when you already started working on it I 
would like to work closely with you and complete the missing parts. 
Please send me your v2 with the relevant fixes as discussed in the above 
mails. I'll also do some testing.

Thanks,
Hadar


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