linux-kernel - Re: A question about acpi_early_init(), and want to invoke acpi_early

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Date:   Thu, 13 Jul 2017 13:53:47 +0800
From:   Dou Liyang <douly.fnst@...fujitsu.com>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        "Rafael J. Wysocki" <rafael@...nel.org>
CC:     ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Julian Wollrath <jwollrath@....de>
Subject: Re: A question about acpi_early_init(), and want to invoke
 acpi_early_init() earlier

Hi, Rafael

At 07/11/2017 09:26 PM, Dou Liyang wrote:
> Hi, Rafael
>
> Recently, I worked for unify the interrupt delivery mode and do its
> setup earlier[1]. And I met a bug about ACPI[2].
>
> When I investigated it, I got your *commit c4e1acbb35e4 (ACPI / init:
> Invoke early ACPI initialization later).*  And I reproduced the
> problem you said.
>
> Question:
> --------
>
> In the changelog of commit c4e1acbb35e4:
>
>> Commit 73f7d1ca3263 (ACPI / init: Run acpi_early_init() before
>> timekeeping_init()) optimistically moved the early ACPI initialization
>> before timekeeping_init(), but that didn't work, because it broke fast
>> TSC calibration for Julian Wollrath on Thinkpad x121e (and most likely
>

Sorry to trouble you again, I forgot cc Julian who reported it. :)

Add Cc: Julian Wollrath.

Thanks,

	dou.

> Here, does the fast TSC calibration means *quick_pit_calibrate()* ?
>
>> for others too).  The reason is that acpi_early_init() enables the SCI
>> and that interferes with the fast TSC calibration mechanism.
>
> I reproduced it by the following command line:
>     ...noapic acpi_sci=level...
>
> the original dmesg is:
>
> [    0.000000] tsc: Fast TSC calibration using PIT
>
> the broken dmesg is:
>
> [    0.001000] tsc: PIT calibration matches HPET. 1 loops
>
> Is it right? If it is wrong, please give the right process for
> reproducing.
>
>>
>> Thus follow the original idea to execute acpi_early_init() before
>> efi_enter_virtual_mode() to help the EFI people for now and we can
>> revisit the other problem that commit 73f7d1ca3263 attempted to
>> address in the future (if really necessary).
>
> If the result which I reproduced was right, I think we can do what
> the commit 73f7d1ca3263 attempted to do now. And it also can fix the
> bug[2].
>
> Because my patchset[1] will setup the interrupt delivery mode earlier
> than TSC initialization. So, in Fast TSC calibration, kernel is in its
> final interrupt mode, not just PIC mode. The change of trigger type
> will never break the Fast TSC calibration(I have tested in my box).
>
>
> [1] https://lkml.org/lkml/2017/6/30/17
> [2] https://lists.gt.net/xen/devel/483350
>
>
> Thanks,
>
>     dou.
>