[PATCH v4 2/3] x86/apic: Introduce a variable to track the number of EILVT registers

[Naveen N Rao (AMD)]

Future AMD processors will be increasing the number of EILVT registers.
Rather than hardcoding the maximum EILVT register count and using that
everywhere, introduce a variable in 'struct apic' to track the EILVT
register count.

The number of EILVT registers is exposed through the extended APIC
Feature Register (APIC_EFEAT) bits 23:16. Use this to initialize the
count and fall back to the current default (APIC_EILVT_NR_AMD_10H) if
the count is not available.

Signed-off-by: Naveen N Rao (AMD) <naveen@xxxxxxxxxx>
Tested-by: Manali Shukla <manali.shukla@xxxxxxx>
---
 arch/x86/include/asm/apic.h    |  2 ++
 arch/x86/include/asm/apicdef.h |  1 +
 arch/x86/kernel/apic/apic.c    | 10 ++++++++++
 3 files changed, 13 insertions(+)

diff --git a/arch/x86/include/asm/apic.h b/arch/x86/include/asm/apic.h
index 9cd493d467d4..578cc28b3134 100644
--- a/arch/x86/include/asm/apic.h
+++ b/arch/x86/include/asm/apic.h
@@ -317,6 +317,8 @@ struct apic {
 
 	void	(*update_vector)(unsigned int cpu, unsigned int vector, bool set);
 
+	u32	eilvt_regs_count;
+
 	char	*name;
 };
 
diff --git a/arch/x86/include/asm/apicdef.h b/arch/x86/include/asm/apicdef.h
index bc125c4429dc..ba7657e75ad1 100644
--- a/arch/x86/include/asm/apicdef.h
+++ b/arch/x86/include/asm/apicdef.h
@@ -134,6 +134,7 @@
 #define		APIC_TDR_DIV_64		0x9
 #define		APIC_TDR_DIV_128	0xA
 #define	APIC_EFEAT	0x400
+#define		APIC_EFEAT_XLC(x)	(((x) >> 16) & 0xff)
 #define	APIC_ECTRL	0x410
 #define APIC_SEOI	0x420
 #define APIC_IER	0x480
diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
index 90025451ace2..c990f403ec7f 100644
--- a/arch/x86/kernel/apic/apic.c
+++ b/arch/x86/kernel/apic/apic.c
@@ -410,6 +410,15 @@ int setup_APIC_eilvt(u8 offset, u8 vector, u8 msg_type, u8 mask)
 }
 EXPORT_SYMBOL_GPL(setup_APIC_eilvt);
 
+static __init void init_eilvt(void)
+{
+	if (cpu_feature_enabled(X86_FEATURE_EXTAPIC))
+		apic->eilvt_regs_count = APIC_EFEAT_XLC(apic_read(APIC_EFEAT));
+
+	if (!apic->eilvt_regs_count && boot_cpu_data.x86_vendor == X86_VENDOR_AMD)
+		apic->eilvt_regs_count = APIC_EILVT_NR_AMD_10H;
+}
+
 /*
  * Program the next event, relative to now
  */
@@ -2345,6 +2354,7 @@ static void __init apic_bsp_setup(bool upmode)
 	if (upmode)
 		apic_bsp_up_setup();
 	setup_local_APIC();
+	init_eilvt();
 
 	enable_IO_APIC();
 	end_local_APIC_setup();
-- 
2.54.0