Choosing between DELAY(useconds) and pause()
julian at freebsd.org
Tue Sep 27 17:11:01 UTC 2011
On 9/27/11 4:12 AM, Gavin Atkinson wrote:
> On Mon, 2011-09-26 at 09:30 -0400, John Baldwin wrote:
>> On Friday, September 23, 2011 11:21:06 am Gavin Atkinson wrote:
>>> On Thu, 2011-09-22 at 20:07 +0200, Hans Petter Selasky wrote:
>>>> On Thursday 22 September 2011 19:55:23 David Somayajulu wrote:
>>>>> It appears that the pause() function cannot be used in driver functions
>>>>> which are invoked early in the boot process. Is there is a kernel api
>>>>> which a device driver can use to determine whether to use pause() or
>>>>> DELAY(), for delays which are say greater than 10hz - may be even 1 hz ?
>>>> Maybe you want to use something like this:
>>>> if (cold)
>>>> In your code.
>>> Note that this still shouldn't be done in your suspend/resume paths, as
>>> "cold" isn't set there, however there also appears to be no guarantee
>>> that pause() will ever return (as you could be running after the timer
>>> has been suspended, or before it resumes).
>>> I'm not sure what the correct answer is for suspend/resume code.
>> Hmmm, on x86 the timers are explicitly shutdown after the DEVICE_SUSPEND()
>> pass over the tree and re-enabled before DEVICE_RESUME(). Perhaps this has
>> changed in HEAD though with the eventtimers stuff. I do think it is best
>> however, to use DELAY() in the suspend/resume path always regardless.
> I don't think head is any different from stable/8 in this respect - the
> same hack patch that fixes suspend/resume for me on head also fixes it
> on stable/8 (the patch basically fakes "cold" during USB
> suspend/resume). See my email to -usb a few months ago:
> I'd really like some guidance as to the correct solution to this, I have
> four separate laptops which fail out of the box on 8 and 9, but
> suspend/resume perfectly with this hack.
code for timers should have a generally readable state that says if
they are useable or not, and we should test that instead of 'cold'
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