Re: [RESEND PATCH v4] clk: stm32h7: Add stm32h743 clock driver

From: Gabriel FERNANDEZ
Date: Wed Jul 05 2017 - 05:35:37 EST

On 06/30/2017 08:54 PM, Stephen Boyd wrote:
> On 06/30, Gabriel FERNANDEZ wrote:
>> On 06/30/2017 02:20 AM, Stephen Boyd wrote:
>>> On 06/29, Gabriel FERNANDEZ wrote:
>>>> On 06/28/2017 05:59 PM, Stephen Boyd wrote:
>>>>> On 06/27, Gabriel FERNANDEZ wrote:
>>>>>> On 06/22/2017 12:07 AM, Stephen Boyd wrote:
>>>>>>> readl_poll_timeout?
>>>>>> if i use readl_poll_timeout (wich use 'ktime_get()') it can be
>>>>>> operational only after the selection of clocksource ? (device_initcall).
>>>>>> And then if a driver turn on a clock before, it could blocked the linux
>>>>>> console ?
>>>>> Ok. I wonder if we could add some sort of starting check to
>>>>> readl_poll_timeout() that tests system_state for booting vs.
>>>>> scheduling? That should be sufficient to handle this case?
>>>> Oops i think i understood my problem...
>>>> i used readl_poll_timeout in atomic context.
>>>> I have to move my code in the .prepare ops.
>>>> If you are ok with that i will send a v5
>>> There's readl_poll_timeout_atomic() for those modes.
>> yes it's exactly the test i made (use 'readl_poll_timeout()_atomic' in
>> .enable ops) but i'm blocked.
>> if i do the same in .prepare ops with 'readl_poll_timeout()' it's ok.
> I'm still confused. readl_poll_timeout_atomic() uses ktime_get(),
> and so does readl_poll_timeout(), so how does moving to the
> prepare op fix the problem? What's the actual problem?
Yes both use ktime_get().

The issue concerns internal/external oscillator clocks (time
stabilization could be long) and
if a driver wants to enable one these clocks before device_initcall().

By default the clocksource is the jiffies until the end of the boot
Then after, the best clocksource is selected (arm_system_timer or stm32
timer, etc...)
There is no problem after because the counter is a hardware register.

But the jiffies counter is incremented by interruption and enable op
does not allow to be interrupted. (we can with prepare op).