ACK: [trusty 1/1] x86, irq, pic: Probe for legacy PIC and set legacy_pic appropriately

[Brad Figg]

On 08/20/2014 05:46 AM, Andy Whitcroft wrote:
> From: "K. Y. Srinivasan" <kys at microsoft.com>
> 
> The legacy PIC may or may not be available and we need a mechanism to
> detect the existence of the legacy PIC that is applicable for all
> hardware (both physical as well as virtual) currently supported by
> Linux.
> 
> On Hyper-V, when our legacy firmware presented to the guests, emulates
> the legacy PIC while when our EFI based firmware is presented we do
> not emulate the PIC. To support Hyper-V EFI firmware, we had to set
> the legacy_pic to the null_legacy_pic since we had to bypass PIC based
> calibration in the early boot code. While, on the EFI firmware, we
> know we don't emulate the legacy PIC, we need a generic mechanism to
> detect the presence of the legacy PIC that is not based on boot time
> state - this became apparent when we tried to get kexec to work on
> Hyper-V EFI firmware.
> 
> This patch implements the proposal put forth by H. Peter Anvin
> <hpa at linux.intel.com>: Write a known value to the PIC data port and
> read it back. If the value read is the value written, we do have the
> PIC, if not there is no PIC and we can safely set the legacy_pic to
> null_legacy_pic. Since the read from an unconnected I/O port returns
> 0xff, we will use ~(1 << PIC_CASCADE_IR) (0xfb: mask all lines except
> the cascade line) to probe for the existence of the PIC.
> 
> In version V1 of the patch, I had cleaned up the code based on comments from Peter.
> In version V2 of the patch, I have addressed additional comments from Peter.
> In version V3 of the patch, I have addressed Jan's comments (JBeulich at suse.com).
> In version V4 of the patch, I have addressed additional comments from Peter.
> 
> Signed-off-by: K. Y. Srinivasan <kys at microsoft.com>
> Link: http://lkml.kernel.org/r/1397501029-29286-1-git-send-email-kys@microsoft.com
> Cc: Thomas Gleixner <tglx at linutronix.de>
> Signed-off-by: H. Peter Anvin <hpa at linux.intel.com>
> 
> (cherry picked from commit e179f6914152eca9b338e7d8445684062f560c55)
> BugLink: http://bugs.launchpad.net/bugs/1317697
> Signed-off-by: Andy Whitcroft <apw at canonical.com>
> ---
>  arch/x86/kernel/cpu/mshyperv.c |  9 ---------
>  arch/x86/kernel/i8259.c        | 20 +++++++++++++++++++-
>  2 files changed, 19 insertions(+), 10 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
> index 832d05a..34b520a 100644
> --- a/arch/x86/kernel/cpu/mshyperv.c
> +++ b/arch/x86/kernel/cpu/mshyperv.c
> @@ -92,15 +92,6 @@ static void __init ms_hyperv_init_platform(void)
>  		lapic_timer_frequency = hv_lapic_frequency;
>  		printk(KERN_INFO "HyperV: LAPIC Timer Frequency: %#x\n",
>  				lapic_timer_frequency);
> -
> -		/*
> -		 * On Hyper-V, when we are booting off an EFI firmware stack,
> -		 * we do not have many legacy devices including PIC, PIT etc.
> -		 */
> -		if (efi_enabled(EFI_BOOT)) {
> -			printk(KERN_INFO "HyperV: Using null_legacy_pic\n");
> -			legacy_pic = &null_legacy_pic;
> -		}
>  	}
>  #endif
>  
> diff --git a/arch/x86/kernel/i8259.c b/arch/x86/kernel/i8259.c
> index 2e977b5..8af8171 100644
> --- a/arch/x86/kernel/i8259.c
> +++ b/arch/x86/kernel/i8259.c
> @@ -299,13 +299,31 @@ static void unmask_8259A(void)
>  static void init_8259A(int auto_eoi)
>  {
>  	unsigned long flags;
> +	unsigned char probe_val = ~(1 << PIC_CASCADE_IR);
> +	unsigned char new_val;
>  
>  	i8259A_auto_eoi = auto_eoi;
>  
>  	raw_spin_lock_irqsave(&i8259A_lock, flags);
>  
> -	outb(0xff, PIC_MASTER_IMR);	/* mask all of 8259A-1 */
> +	/*
> +	 * Check to see if we have a PIC.
> +	 * Mask all except the cascade and read
> +	 * back the value we just wrote. If we don't
> +	 * have a PIC, we will read 0xff as opposed to the
> +	 * value we wrote.
> +	 */
>  	outb(0xff, PIC_SLAVE_IMR);	/* mask all of 8259A-2 */
> +	outb(probe_val, PIC_MASTER_IMR);
> +	new_val = inb(PIC_MASTER_IMR);
> +	if (new_val != probe_val) {
> +		printk(KERN_INFO "Using NULL legacy PIC\n");
> +		legacy_pic = &null_legacy_pic;
> +		raw_spin_unlock_irqrestore(&i8259A_lock, flags);
> +		return;
> +	}
> +
> +	outb(0xff, PIC_MASTER_IMR);	/* mask all of 8259A-1 */
>  
>  	/*
>  	 * outb_pic - this has to work on a wide range of PC hardware.
> 

Looks like a clean cherry-pick

-- 
Brad Figg brad.figg at canonical.com http://www.canonical.com