linux-kernel - Re: [PATCH 2/7] clocksource: Add Tegra186 timers support

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Date:   Mon, 23 Mar 2020 14:38:35 +0100
From:   Thierry Reding <thierry.reding@...il.com>
To:     Dmitry Osipenko <digetx@...il.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Rob Herring <robh+dt@...nel.org>,
        Jon Hunter <jonathanh@...dia.com>, linux-tegra@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/7] clocksource: Add Tegra186 timers support

On Fri, Mar 20, 2020 at 06:23:35PM +0300, Dmitry Osipenko wrote:
> 20.03.2020 18:04, Thierry Reding пишет:
> > On Fri, Mar 20, 2020 at 05:39:01PM +0300, Dmitry Osipenko wrote:
> >> 20.03.2020 16:34, Thierry Reding пишет:
> >>> From: Thierry Reding <treding@...dia.com>
> >>>
> >>> Currently this only supports a single watchdog, which uses a timer in
> >>> the background for countdown. Eventually the timers could be used for
> >>> various time-keeping tasks, but by default the architected timer will
> >>> already provide that functionality.
> >>>
> >>> Signed-off-by: Thierry Reding <treding@...dia.com>
> >>> ---
> >>>  drivers/clocksource/Kconfig          |   8 +
> >>>  drivers/clocksource/Makefile         |   1 +
> >>>  drivers/clocksource/timer-tegra186.c | 377 +++++++++++++++++++++++++++
> >>>  3 files changed, 386 insertions(+)
> >>>  create mode 100644 drivers/clocksource/timer-tegra186.c
> >> Hello Thierry,
> >>
> >> Shouldn't this driver reside in drivers/watchdog/? Like it's done in a
> >> case of the T30+ driver.
> > 
> > The hardware block that this binds to is primarily a time-keeping block
> > that just so happens to also implement a watchdog. Moving this to
> > drivers/watchdog would put us into an odd situation if we ever added
> > code to also implement the time-keeping bits for this hardware.
> > 
> > I also think that the way this is done on Tegra30 was a bad choice. The
> > problem is that we now have two drivers (tegra_wdt.c and tegra-timer.c)
> > that both access the same region of memory. This seems to be relatively
> > safe to do on those chips because there's no overlap between the timer
> > and the watchdog interfaces, but on Tegra186 and later the watchdog is
> > actually using one of the timers, so we'd have to be extra careful how
> > to coordinate between the two. It seems much easier to do that by having
> > everything in the same driver and have that register multiple devices in
> > the system.
> 
> Sounds like a watchdog on Tegra20, where one of the timer is shared with
> a watchdog function and there are no other free timers. Well, yes, it's
> not nice.
> 
> But, will you really ever need an additional clocksource on T186?

I don't know. It's possible that they will become useful at some point.

Thierry

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