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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.

  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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