| Message ID | 1408538794-18234-2-git-send-email-apw@canonical.com |
|---|---|
| State | New |
| Headers | show |
On 08/20/2014 05:46 AM, Andy Whitcroft wrote: > From: "K. Y. Srinivasan" <kys@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@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@suse.com). > In version V4 of the patch, I have addressed additional comments from Peter. > > Signed-off-by: K. Y. Srinivasan <kys@microsoft.com> > Link: http://lkml.kernel.org/r/1397501029-29286-1-git-send-email-kys@microsoft.com > Cc: Thomas Gleixner <tglx@linutronix.de> > Signed-off-by: H. Peter Anvin <hpa@linux.intel.com> > > (cherry picked from commit e179f6914152eca9b338e7d8445684062f560c55) > BugLink: http://bugs.launchpad.net/bugs/1317697 > Signed-off-by: Andy Whitcroft <apw@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
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.