From: Hans de Goede <hdegoede@redhat.com>
To: Siarhei Siamashka <siarhei.siamashka@gmail.com>
Cc: linux-sunxi@googlegroups.com, maxime.ripard@free-electrons.com,
John Stultz <john.stultz@linaro.org>,
Thomas Gleixner <tglx@linutronix.de>,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, Emilio Lopez <emilio@elopez.com.ar>,
kevin@allwinnertech.com, sunny@allwinnertech.com,
shuge@allwinnertech.com
Subject: Re: [linux-sunxi] [PATCH 0/8] clocksource: sunxi: Timer fixes and cleanup
Date: Fri, 28 Jun 2013 10:17:57 +0200 [thread overview]
Message-ID: <51CD46B5.6090101@redhat.com> (raw)
In-Reply-To: <20130627232608.1174558b@i7>
Hi,
On 06/27/2013 10:26 PM, Siarhei Siamashka wrote:
> On Thu, 27 Jun 2013 18:54:36 +0200
> Maxime Ripard <maxime.ripard@free-electrons.com> wrote:
>
>> On Thu, Jun 27, 2013 at 11:54:11AM +0200, Hans de Goede wrote:
>>> I notice that unlike the sunxi-3.4 code you don't do any locking,
>>> so how do you stop 2 clocksource calls from racing (and thus
>>> getting a possible wrong value because of things not
>>> being properly latched) ?
>>
>> Hmm, right. I'll add a spinlock.
>
> I think the best would be to ask the Allwinner people (it's good to
> have them in CC, right?) whether anything wrong can happen because of
> "things not being properly latched".
>
> The A10 manual from http://free-electrons.com/~maxime/pub/datasheet/
> does not seem to contain any details about what bad things may happen
> if we try to read CNT64_LO_REG while latching is still in progress and
> CNT64_RL_EN bit in CNT64_CTRL_REG has not changed to zero yet.
> I can imagine the following possible scenarios:
> 1. We read either the old stale CNT64_LO_REG value or the new
> correct value.
> 2. We read either the old stale CNT64_LO_REG value or the new
> correct value, or some random garbage.
> 3. The processor may deadlock, eat your dog, or do some other
> nasty thing.
>
> In the case of 1, we probably can get away without using any spinlocks?
No, because if ie CNT64_LO_REG old is 0xffffffff and CNT64_LO_REG new is
say 0x00000001, and we do get the new CNT64_HI_REG things will break.
Regards,
Hans
next prev parent reply other threads:[~2013-06-28 8:13 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-06-26 21:16 [PATCH 0/8] clocksource: sunxi: Timer fixes and cleanup Maxime Ripard
2013-06-26 21:16 ` [PATCH 1/8] clocksource: sun4i: Use the BIT macros where possible Maxime Ripard
2013-06-26 21:16 ` [PATCH 2/8] clocksource: sun4i: Add clocksource and sched clock drivers Maxime Ripard
2013-06-26 21:27 ` Daniel Lezcano
2013-06-27 9:31 ` Maxime Ripard
2013-06-27 6:02 ` Baruch Siach
2013-06-27 9:35 ` Maxime Ripard
2013-06-27 9:46 ` Baruch Siach
2013-06-27 17:21 ` Maxime Ripard
2013-06-27 17:36 ` Baruch Siach
2013-06-27 19:16 ` Maxime Ripard
2013-06-27 10:17 ` [linux-sunxi] " Siarhei Siamashka
2013-06-27 17:02 ` Maxime Ripard
2013-06-27 19:51 ` Siarhei Siamashka
2013-06-28 10:19 ` Maxime Ripard
2013-06-26 21:16 ` [PATCH 3/8] clocksource: sun4i: Don't forget to enable the clock we use Maxime Ripard
2013-06-26 21:16 ` [PATCH 4/8] clocksource: sun4i: Fix the next event code Maxime Ripard
2013-06-26 21:16 ` [PATCH 5/8] clocksource: sun4i: Factor out some timer code Maxime Ripard
2013-06-26 21:16 ` [PATCH 6/8] clocksource: sun4i: Remove TIMER_SCAL variable Maxime Ripard
2013-06-26 21:17 ` [PATCH 7/8] clocksource: sun4i: Cleanup parent clock setup Maxime Ripard
2013-06-26 21:17 ` [PATCH 8/8] clocksource: sun4i: Fix bug when switching from periodic to oneshot modes Maxime Ripard
2013-06-27 9:27 ` [linux-sunxi] [PATCH 0/8] clocksource: sunxi: Timer fixes and cleanup Hans de Goede
2013-06-27 9:43 ` Maxime Ripard
2013-06-27 9:54 ` Hans de Goede
2013-06-27 16:54 ` Maxime Ripard
2013-06-27 18:13 ` Hans de Goede
2013-06-28 10:41 ` Maxime Ripard
2013-06-27 20:26 ` Siarhei Siamashka
2013-06-28 8:17 ` Hans de Goede [this message]
[not found] ` <2013062809433715678058@allwinnertech.com>
[not found] ` <20130628124843.242df804@i7>
2013-06-28 10:26 ` Thomas Gleixner
2013-06-28 11:14 ` Siarhei Siamashka
2013-06-28 14:02 ` Thomas Gleixner
2013-06-28 17:03 ` maxime.ripard
[not found] ` <20130628132912.014b2f5b@i7>
2013-06-28 14:16 ` maxime.ripard
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