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

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Date:   Tue, 16 Apr 2019 20:03:46 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Helge Deller <deller@....de>
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 Tue, Apr 16, 2019 at 05:00:15PM +0200, Helge Deller wrote:
> 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.

Ok, I've pulled that patch in now as well, let me regenerate the tree
and see if that solves the issue or not.

thanks,

greg k-h