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To:     linux-kernel@vger.kernel.org
From:   Helge Deller <deller@gmx.de>
Subject: Re: [PATCH 4.9 64/76] parisc: Detect QEMU earlier in boot process
Date:   Tue, 16 Apr 2019 15:49:47 +0200
Message-ID: <26f36020-9c8f-0559-7692-56fe88f5f6c1@gmx.de>
References: <20190415183707.712011689@linuxfoundation.org>
 <20190415183726.478117691@linuxfoundation.org>
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Hi Greg,

please do NOT apply this patch to the 4.9 tree.
See below, it was tagged for v4.14+ only.
It breaks the build on 4.9, I got a 0-day build bug about it.

Thanks,
Helge


On 15.04.19 20:44, Greg Kroah-Hartman wrote:
> From: Helge Deller <deller@gmx.de>
> 
> 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")
> Signed-off-by: Helge Deller <deller@gmx.de>
> Cc: stable@vger.kernel.org # v4.14+
> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> 
> ---
>  arch/parisc/kernel/process.c |    6 ------
>  arch/parisc/kernel/setup.c   |    3 +++
>  2 files changed, 3 insertions(+), 6 deletions(-)
> 
> --- a/arch/parisc/kernel/process.c
> +++ b/arch/parisc/kernel/process.c
> @@ -206,12 +206,6 @@ void __cpuidle arch_cpu_idle(void)
>  
>  static int __init parisc_idle_init(void)
>  {
> -	const char *marker;
> -
> -	/* check QEMU/SeaBIOS marker in PAGE0 */
> -	marker = (char *) &PAGE0->pad0;
> -	running_on_qemu = (memcmp(marker, "SeaBIOS", 8) == 0);
> -
>  	if (!running_on_qemu)
>  		cpu_idle_poll_ctrl(1);
>  
> --- a/arch/parisc/kernel/setup.c
> +++ b/arch/parisc/kernel/setup.c
> @@ -403,6 +403,9 @@ void start_parisc(void)
>  	int ret, cpunum;
>  	struct pdc_coproc_cfg coproc_cfg;
>  
> +	/* check QEMU/SeaBIOS marker in PAGE0 */
> +	running_on_qemu = (memcmp(&PAGE0->pad0, "SeaBIOS", 8) == 0);
> +
>  	cpunum = smp_processor_id();
>  
>  	set_firmware_width_unlocked();
> 
> 
>