Messages in this thread | | | Date | Sat, 15 Jan 2011 18:07:38 +0100 | From | Christer Weinigel <> | Subject | Re: Locking in the clk API |
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On 01/15/2011 03:53 PM, Russell King - ARM Linux wrote: > On Sat, Jan 15, 2011 at 03:02:25PM +0100, Christer Weinigel wrote: >> On platforms that need to sleep to enable the UART clock, configuring >> the UART as the kernel console should be equivalent to userspace opening >> the UART device, i.e. enable the clock. At least to me that feels like >> an acceptable tradeoff, and if I wanted to save the last bit of power >> I'll have to refrain from using UART as the kernel console. > > Well, we're not discussing a _new_ API here - we're discussing an API > with existing users which works completely fine on the devices its > used, with differing expectations between implementations.
Yes, so to fulfil the requirement that printk needs to call clk_enable from atomic contexts, document that clk_enable can not sleep. Or add the clk_enable_atomic call and modify printk to use it.
>> Both of these feel like they should use a call such as clk_get_atomic >> and be able to handle EWOULDBLOCK/EAGAIN (or whatever error code is used >> to indicate that it would have to sleep) and delegate to a worker thread >> to enable the clock. To catch uses of plain clk_enable from atomic >> contects, add a WARN_ON/BUG_ON(in_atomic()). It won't catch everything, >> but would help a bit at least. > > We've never allowed clk_get() to be called in interruptible context, > so that's not the issue. The issue is purely about clk_enable() and > clk_disable() and whether they should be able to be called in atomic > context or not.
My bad, it should have said "clk_enable_atomic".
> There's been a lot of talk on this issue for ages with no real progress > that I'm just going to repeat: let's unify those implementations which > use a spinlock for their clks into one consolidated solution, and > a separate consolidated solution for those which use a mutex. > > This will at least allow us to have _some_ consolidation of the existing > implementations - and it doesn't add anything to the problem at hand. > It might actually help identify what can be done at code level to resolve > this issue.
Won't that cause a lot of code duplication? If it's possible to have one sane implementation, why not go for it at once?
/Christer
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