arm64: Relax GIC version check during early boot

[ Upstream commit 74698f6971f25d045301139413578865fc2bd8f9 ]

Updates to the GIC architecture allow ID_AA64PFR0_EL1.GIC to have
values other than 0 or 1. At the moment, Linux is quite strict in the
way it handles this field at early boot stage (cpufeature is fine) and
will refuse to use the system register CPU interface if it doesn't
find the value 1.

Fixes: 021f653791ad17e03f98aaa7fb933816ae16f161 ("irqchip: gic-v3: Initial support for GICv3")
Reported-by: Chase Conklin <Chase.Conklin@arm.com>
Reviewed-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Vladimir Murzin <vladimir.murzin@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
index 0382eba4bf7b23fd40d235f67db786b29b5aff44..6299a8a361eeeb19f341ccaf5b39a0aeb64c3c7a 100644 (file)
--- a/arch/arm64/kernel/head.S
+++ b/arch/arm64/kernel/head.S
@@ -478,8 +478,7 @@ CPU_LE(     bic     x0, x0, #(3 << 24)      )       // Clear the EE and E0E bits for EL1
        /* GICv3 system register access */
        mrs     x0, id_aa64pfr0_el1
        ubfx    x0, x0, #24, #4
-       cmp     x0, #1
-       b.ne    3f
+       cbz     x0, 3f
 
        mrs_s   x0, ICC_SRE_EL2
        orr     x0, x0, #ICC_SRE_EL2_SRE        // Set ICC_SRE_EL2.SRE==1