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

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Date:   Wed, 5 Jul 2017 09:27:14 +0000
From:   Gabriel FERNANDEZ <gabriel.fernandez@...com>
To:     Stephen Boyd <sboyd@...eaurora.org>
CC:     Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Russell King <linux@...linux.org.uk>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Alexandre TORGUE <alexandre.torgue@...com>,
        Michael Turquette <mturquette@...libre.com>,
        Nicolas Pitre <nico@...aro.org>, Arnd Bergmann <arnd@...db.de>,
        "daniel.thompson@...aro.org" <daniel.thompson@...aro.org>,
        "andrea.merello@...il.com" <andrea.merello@...il.com>,
        "radoslaw.pietrzyk@...il.com" <radoslaw.pietrzyk@...il.com>,
        Lee Jones <lee.jones@...aro.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-clk@...r.kernel.org" <linux-clk@...r.kernel.org>,
        Ludovic BARRE <ludovic.barre@...com>,
        "Olivier BIDEAU" <olivier.bideau@...com>,
        Amelie DELAUNAY <amelie.delaunay@...com>,
        "gabriel.fernandez.st@...il.com" <gabriel.fernandez.st@...il.com>
Subject: Re: [RESEND PATCH v4] clk: stm32h7: Add stm32h743 clock driver



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 
(fs_initcall)
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).