From: Thierry Reding <thierry.reding@gmail.com>
To: Dipen Patel <dipenp@nvidia.com>
Cc: Richard Cochran <richardcochran@gmail.com>,
Arnd Bergmann <arnd@arndb.de>,
Linus Walleij <linus.walleij@linaro.org>,
Kent Gibson <warthog618@gmail.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Jon Hunter <jonathanh@nvidia.com>,
Bartosz Golaszewski <bgolaszewski@baylibre.com>,
"open list:GPIO SUBSYSTEM" <linux-gpio@vger.kernel.org>,
linux-tegra <linux-tegra@vger.kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Networking <netdev@vger.kernel.org>
Subject: Re: GTE - The hardware timestamping engine
Date: Tue, 23 Mar 2021 10:03:18 +0100 [thread overview]
Message-ID: <YFmu1pptAFQLABe3@orome.fritz.box> (raw)
In-Reply-To: <a58a0ec2-9da8-92bc-c08e-38b1bed6f757@nvidia.com>
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On Mon, Mar 22, 2021 at 01:33:38PM -0700, Dipen Patel wrote:
> Hi Richard,
>
> Thanks for your input and time. Please see below follow up.
>
> On 3/20/21 8:38 AM, Richard Cochran wrote:
> > On Sat, Mar 20, 2021 at 01:44:20PM +0100, Arnd Bergmann wrote:
> >> Adding Richard Cochran as well, for drivers/ptp/, he may be able to
> >> identify whether this should be integrated into that framework in some
> >> form.
> >
> > I'm not familiar with the GTE, but it sounds like it is a (free
> > running?) clock with time stamping inputs. If so, then it could
> > expose a PHC. That gets you functionality:
> >
> > - clock_gettime() and friends
> > - comparison ioctl between GTE clock and CLOCK_REALTIME
> > - time stamping channels with programmable input selection
> >
> GTE gets or rather records the timestamps from the TSC
> (timestamp system coutner) so its not attached to GTE as any
> one can access TSC, so not sure if we really need to implement PHC
> and/or clock_* and friends for the GTE. I believe burden to find correlation
> between various clock domains should be on the clients, consider below
> example.
I agree. My understanding is the the TSC is basically an SoC-wide clock
that can be (and is) used by several hardware blocks. There's an
interface for software to read out the value, but it's part of a block
called TKE (time-keeping engine, if I recall correctly) that implements
various clock sources and watchdog functionality.
As a matter of fact, I recall typing up a driver for that at some point
but I don't recall if I ever sent it out or what became of it. I can't
find it upstream at least.
Anyway, I think given that the GTE doesn't provide that clock itself but
rather just a means of taking a snapshot of that clock and stamping
certain events with that, it makes more sense to provide that clock from
the TKE driver.
Thierry
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next prev parent reply other threads:[~2021-03-23 9:03 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-17 22:33 GTE - The hardware timestamping engine Dipen Patel
2021-03-20 11:56 ` Linus Walleij
2021-03-20 12:44 ` Arnd Bergmann
2021-03-20 15:38 ` Richard Cochran
2021-03-22 20:33 ` Dipen Patel
2021-03-23 9:03 ` Thierry Reding [this message]
2021-03-23 12:51 ` Richard Cochran
2021-03-22 6:00 ` Kent Gibson
2021-03-22 20:21 ` Dipen Patel
2021-03-23 0:32 ` Kent Gibson
2021-03-23 1:53 ` Dipen Patel
2021-03-23 2:59 ` Kent Gibson
2021-03-23 4:09 ` Dipen Patel
2021-03-23 5:22 ` Kent Gibson
2021-03-23 9:08 ` Linus Walleij
2021-03-23 10:06 ` Thierry Reding
2021-03-23 18:21 ` Marc Zyngier
2021-03-23 18:25 ` Dipen Patel
2021-03-23 21:19 ` Dipen Patel
2021-03-23 18:01 ` Dipen Patel
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