Locking in the clk API, part 2: clk_prepare/clk_unprepare

[Saravana Kannan]

On 02/01/2011 11:56 AM, Russell King - ARM Linux wrote:
> On Tue, Feb 01, 2011 at 08:32:01PM +0100, Uwe Kleine-König wrote:
>> On Tue, Feb 01, 2011 at 05:06:37PM +0000, Russell King - ARM Linux wrote:
>>> So?  You're not _supposed_ to call it from any atomic context ever.
>>
>> My motivation for a more complicated clk_prepare was to make clk_prepare
>> atomic when that's possible (i.e. when the clk is already prepared) and
>> call it before the enable callback in clk_enable.  Then everything
>> behaves nicely even if clk_enable is called from atomic context provided
>> that the clock was prepared before (or doesn't need to).
>
> You really don't get the point of clk_prepare() do you.  I'm not
> going to bother trying to educate you anymore.
>
> Hopefully someone with more patience can give you the necessary
> teaching to make you understand.

Uwe,

If the driver is calling clk_prepare() right next to clk_enable() 
knowing it's been already prepared and will hence be "atomic" (this is 
actually not true), then by your description, it's pointless to call 
clk_prepare().

If you want the driver to call clk_prepare() in atomic context because 
it will be atomic in most cases -- well, that's wrong. It's either 
atomic or is NOT atomic. There is no in between. If a call is NOT 
atomic, it can't be called in atomic context. Long story short, if you 
expect clk_prepare() to be atomic under any circumstance, it beats the 
point of introducing clk_prepare().

Hope I helped.

-Saravana

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