From: skannan@codeaurora.org (Saravana Kannan)
To: linux-arm-kernel@lists.infradead.org
Subject: Locking in the clk API
Date: Fri, 21 Jan 2011 17:35:42 -0800 [thread overview]
Message-ID: <4D3A346E.9070709@codeaurora.org> (raw)
In-Reply-To: <AANLkTimT+vfg9p4GSnn1jGW9r_gVom7xEUzMVJDscPg2@mail.gmail.com>
On 01/21/2011 02:28 PM, Colin Cross wrote:
> On Fri, Jan 21, 2011 at 2:02 PM, Russell King - ARM Linux
> <linux@arm.linux.org.uk> wrote:
>> On Fri, Jan 21, 2011 at 04:53:44PM -0500, Nicolas Pitre wrote:
>>> So I think that the API must be augmented with more methods, such as:
>>>
>>> clk_slow_enable():
>>> - may sleep
>>> - may be a no-op if the clk_fast_enable() is supported
>>>
>>> clk_fast_enable():
>>> - may not sleep, used in atomic context
>>> - may be a no-op if controlling the clock takes time, in which case
>>> clk_slow_enable() must have set the clock up entirely
>>>
>>> ... and similar for clk_slow_disable() and clk_fast_disable().
>>
>> Isn't this along the same lines as my clk_prepare() vs clk_enable()
>> suggestion?
>>
>> I suggested that clk_prepare() be callable only from non-atomic contexts,
>> and do whatever's required to ensure that the clock is available. That
>> may end up enabling the clock as a result.
>>
>> clk_enable() callable from atomic contexts, and turns the clock on if
>> the hardware supports such an operation.
>>
>> So, if you have something like:
>>
>> Xtal--->PLL--->Routing/Masking--->Device
>>
>> clk = clk_get() returns the clock for the device.
>>
>> clk_prepare(clk) would walk up the clock tree, selecting the routing and
>> preparing each clock. Clocks prior to _and_ including the PLL would need
>> to be enabled.
>>
>> clk_enable(clk) would walk up the tree if the clock isn't already enabled,
>> calling clk_enable() on the parent clock. As we require prepared clocks
>> to already be enabled, this automatically stops at the PLL.
>>
>> To encourage correct usage, we just need to make sure that clk_prepare()
>> has a might_sleep() thing, and clk_enable() throws a fit if it's used
>> on a clk without prepare being used first. The second point is not easy
>> to do in a foolproof manner though, but doing _something_ is better than
>> nothing.
>
> I like this proposal, and I prefer the clk_prepare naming over
> clk_slow_enable - too many people would call clk_slow_enable instead
> of, and not as well as, clk_fast_enable.
>
> On Tegra, I currently use the ugly conditional mutex or spinlock
> method to deal with voltage scaling based on clock frequency.
Colin,
MSM is in a similar situation, so thought I should bring this up to you
attention -- do you have no use case for changing the rate in atomic
context? If you do, the clk_prepare/unprepare() approach won't work.
Do you have no such requirement?
-Saravana
--
Sent by an employee of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.
next prev parent reply other threads:[~2011-01-22 1:35 UTC|newest]
Thread overview: 86+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-01-11 2:16 Locking in the clk API Jeremy Kerr
2011-01-11 3:15 ` Paul Mundt
2011-01-11 4:11 ` Jeremy Kerr
2011-01-11 4:54 ` Paul Mundt
2011-01-20 16:32 ` Ben Dooks
2011-01-20 18:57 ` Russell King - ARM Linux
2011-01-21 3:43 ` Saravana Kannan
2011-01-21 9:31 ` Russell King - ARM Linux
2011-01-11 9:03 ` Sascha Hauer
2011-01-11 9:28 ` Russell King - ARM Linux
2011-01-11 14:34 ` Pavel Machek
2011-01-20 16:29 ` Ben Dooks
2011-01-20 18:56 ` Russell King - ARM Linux
2011-01-20 21:30 ` Nicolas Pitre
2011-01-21 2:06 ` Dima Zavin
2011-01-21 4:12 ` Saravana Kannan
2011-01-21 9:32 ` Russell King - ARM Linux
2011-01-22 1:53 ` Saravana Kannan
2011-01-22 2:24 ` Colin Cross
2011-01-22 2:56 ` Saravana Kannan
2011-01-22 9:15 ` Russell King - ARM Linux
2011-01-24 19:31 ` Saravana Kannan
2011-01-21 21:03 ` Dima Zavin
2011-01-21 21:53 ` Nicolas Pitre
2011-01-21 22:02 ` Russell King - ARM Linux
2011-01-21 22:28 ` Colin Cross
2011-01-21 23:21 ` Benjamin Herrenschmidt
2011-01-21 23:50 ` Nicolas Pitre
2011-01-22 1:35 ` Saravana Kannan [this message]
2011-01-22 2:22 ` Colin Cross
2011-01-21 22:29 ` Nicolas Pitre
2011-01-21 23:28 ` Bryan Huntsman
2011-01-11 9:16 ` Russell King - ARM Linux
2011-01-11 9:44 ` Jeremy Kerr
2011-01-11 10:13 ` Paul Mundt
2011-01-11 10:30 ` Jeremy Kerr
2011-01-11 12:18 ` Paul Mundt
2011-01-11 13:52 ` Uwe Kleine-König
2011-01-11 14:35 ` Jeremy Kerr
2011-01-12 3:25 ` Saravana Kannan
2011-01-12 7:40 ` Uwe Kleine-König
2011-01-12 1:54 ` Saravana Kannan
2011-01-12 2:25 ` Paul Mundt
2011-01-20 16:57 ` Ben Dooks
2011-01-20 16:53 ` Ben Dooks
2011-01-20 16:40 ` Ben Dooks
2011-01-11 10:39 ` Uwe Kleine-König
2011-01-11 10:47 ` Russell King - ARM Linux
2011-01-11 10:56 ` Uwe Kleine-König
2011-01-11 11:15 ` Richard Zhao
2011-01-20 17:02 ` Ben Dooks
2011-01-20 19:08 ` Russell King - ARM Linux
2011-01-21 0:09 ` Jassi Brar
2011-01-21 4:47 ` Jassi Brar
2011-01-21 9:39 ` Russell King - ARM Linux
2011-01-21 10:11 ` Jassi Brar
2011-01-22 4:08 ` Richard Zhao
2011-01-22 5:30 ` Jassi Brar
2011-01-21 7:16 ` Saravana Kannan
2011-01-21 9:40 ` Russell King - ARM Linux
2011-01-22 1:47 ` Saravana Kannan
2011-01-27 4:34 ` Saravana Kannan
2011-01-27 8:54 ` Russell King - ARM Linux
2011-01-27 20:30 ` Saravana Kannan
2011-01-27 20:43 ` Russell King - ARM Linux
2011-01-27 21:07 ` Alan Cox
2011-01-27 21:11 ` Russell King - ARM Linux
2011-01-27 21:15 ` Russell King - ARM Linux
2011-01-28 3:29 ` Saravana Kannan
2011-01-28 3:27 ` Saravana Kannan
2011-01-11 12:11 ` Jassi Brar
2011-01-12 2:56 ` Saravana Kannan
2011-01-12 9:03 ` Russell King - ARM Linux
2011-01-15 14:02 ` Christer Weinigel
2011-01-15 14:53 ` Russell King - ARM Linux
2011-01-15 15:03 ` Uwe Kleine-König
2011-01-15 15:15 ` Russell King - ARM Linux
2011-01-15 16:03 ` Uwe Kleine-König
2011-01-15 16:21 ` Russell King - ARM Linux
2011-01-15 16:31 ` Uwe Kleine-König
2011-01-16 6:59 ` Grant Likely
2011-01-15 17:07 ` Christer Weinigel
2011-01-15 17:20 ` Russell King - ARM Linux
2011-01-15 17:44 ` Christer Weinigel
2011-01-15 20:30 ` Russell King - ARM Linux
2011-01-17 1:19 ` Jeremy Kerr
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