linux-kernel - Re: [PATCH 4.9 64/76] parisc: Detect QEMU earlier in boot process

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Message-ID: <b73a9caf-2461-3361-a6ed-b36a5d0a06c9@gmx.de>
Date:   Tue, 16 Apr 2019 17:00:15 +0200
From:   Helge Deller <deller@....de>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Linux Kernel Development <linux-kernel@...r.kernel.org>,
        stable@...r.kernel.org
Subject: Re: [PATCH 4.9 64/76] parisc: Detect QEMU earlier in boot process

On 16.04.19 16:23, Greg Kroah-Hartman wrote:
> On Tue, Apr 16, 2019 at 03:50:16PM +0200, Helge Deller wrote:
>> Hi Greg,
>>
>> please do NOT apply this patch to the 4.9 tree.
>> See below, it was tagged for v4.14+ only.
>
> Yes, but I added it to 4.9 because:

Ah, ok.

>>> commit d006e95b5561f708d0385e9677ffe2c46f2ae345 upstream.
>>>
>>> While adding LASI support to QEMU, I noticed that the QEMU detection in
>>> the kernel happens much too late. For example, when a LASI chip is found
>>> by the kernel, it registers the LASI LED driver as well.  But when we
>>> run on QEMU it makes sense to avoid spending unnecessary CPU cycles, so
>>> we need to access the running_on_QEMU flag earlier than before.
>>>
>>> This patch now makes the QEMU detection the fist task of the Linux
>>> kernel by moving it to where the kernel enters the C-coding.
>>>
>>> Fixes: 310d82784fb4 ("parisc: qemu idle sleep support")
>
> This commit is in 4.9.76.  So why wouldn't it be valid in 4.9.y (with
> the exception of the fact that it doesn't build...)?

In my opinion it was not a critical-enough patch to ask for backporting this
and the other depend patch.
Idle-sleep does work without this patch, it's just upcoming qemu-support
wich will not run optimal (but does work).

That said, of course it would be nice to get that backported in 4.9.
I *think* if you pull in 5ffa8518851f1401817c15d2a7eecc0373c26ff9 too,
it should be ok and fix the build issue.

Helge