linux-kernel - Re: [PATCH net-next V2 19/23] ptp: tilegx: convert to the 64 bit get/set time methods.

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Date:	Mon, 23 Mar 2015 13:26:22 -0400
From:	Chris Metcalf <cmetcalf@...hip.com>
To:	Richard Cochran <richardcochran@...il.com>
CC:	<netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	Amir Vadai <amirv@...lanox.com>,
	Ariel Elior <ariel.elior@...gic.com>,
	Arnd Bergmann <arnd@...aro.org>,
	Baolin Wang <baolin.wang@...aro.org>,
	Ben Hutchings <ben@...adent.org.uk>,
	Bruce Allan <bruce.w.allan@...el.com>,
	Carolyn Wyborny <carolyn.wyborny@...el.com>,
	David Miller <davem@...emloft.net>,
	Frank Li <Frank.Li@...escale.com>,
	Giuseppe Cavallaro <peppe.cavallaro@...com>,
	Jeff Kirsher <jeffrey.t.kirsher@...el.com>,
	John Stultz <john.stultz@...aro.org>,
	Luwei Zhou <b45643@...escale.com>,
	Matthew Vick <matthew.vick@...el.com>,
	Michael Chan <mchan@...adcom.com>,
	Prashant Sreedharan <prashant@...adcom.com>,
	Shradha Shah <sshah@...arflare.com>,
	Solarflare linux maintainers <linux-net-drivers@...arflare.com>,
	Sonic Zhang <sonic.zhang@...log.com>,
	Stefan Sørensen 
	<stefan.sorensen@...ctralink.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Tom Lendacky <thomas.lendacky@....com>
Subject: Re: [PATCH net-next V2 19/23] ptp: tilegx: convert to the 64 bit
 get/set time methods.

On 03/23/2015 12:58 PM, Richard Cochran wrote:
> On Mon, Mar 23, 2015 at 12:02:03PM -0400, Chris Metcalf wrote:
>> >This driver is 64-bit only.  Would it make more sense to just change
>> >the accessors from gettime/settime to gettime/settime64 and nothing
>> >else, i.e. rely on the current behavior that timespec and timespec64
>> >are the same type, and trust the compiler to fail it if somehow someone
>> >tried to build this driver into a 32-bit kernel?
> On the one hand, I think the best way would be for
> gxio_mpipe_get/set_timestamp to also take a timespec64, because it
> makes the width clear.  With a plain old timespec, you have to
> remember whether you are 64 bit or not.  However, but I couldn't tell
> if changing gxio_mpipe_get/set_timestamp would work for other callers
> or not.

If you're suggesting changing the gxio_mpipe_xxx_timespec routines
to take a timespec64, that sounds reasonable to me, particularly in
conjunction with your new gettime64 etc API.

As far as I know, the tilegx driver is the only client of those gxio
routines.

> If the driver is 64 bit only, shouldn't that be reflected in the
> Kconfig?

Well, the tilegx driver is only supported for the tilegx architecture,
which is only 64-bit for kernel-space.  It may be a bit confusing
because the actual driver is tile_net, which has separate implementations
for tilegx (64-bit) and tilepro (32-bit).  It's not immediately clear how
to make that more obvious.

> On the other hand, I wouldn't mind the change you suggest, if it were
> super obvious that the code is 64 bit only.  It was not obvious to me.

I guess that brings us back to changing the gxio_xxx APIs.

-- 
Chris Metcalf, EZChip Semiconductor
http://www.ezchip.com

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