[PATCH v2] ARM: virt: Relax arch timer version check during early boot

[PATCH v2] ARM: virt: Relax arch timer version check during early boot

[Vladimir Murzin]

Updates to the Generic Timer architecture allow ID_PFR1.GenTimer to
have values other than 0 or 1 while still preserving backward
compatibility. At the moment, Linux is quite strict in the way it
handles this field at early boot and will not configure arch timer if
it doesn't find the value 1.

Since here use ubfx for arch timer version extraction (hyb-stub build
with -march=armv7-a, so it is safe)

To help backports (even though the code was correct at the time of writing)
Fixes: 8ec58be9f3ff ("ARM: virt: arch_timers: enable access to physical timers")
Signed-off-by: Vladimir Murzin <vladimir.murzin@arm.com>
---

Changelog:

    v1 -> v2
       - Clarify that backward compatibility is preserved (per Marc)

 arch/arm/kernel/hyp-stub.S | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/arch/arm/kernel/hyp-stub.S b/arch/arm/kernel/hyp-stub.S
index ae50203..6607fa8 100644
--- a/arch/arm/kernel/hyp-stub.S
+++ b/arch/arm/kernel/hyp-stub.S
@@ -146,10 +146,9 @@ ARM_BE8(orr	r7, r7, #(1 << 25))     @ HSCTLR.EE
 #if !defined(ZIMAGE) && defined(CONFIG_ARM_ARCH_TIMER)
 	@ make CNTP_* and CNTPCT accessible from PL1
 	mrc	p15, 0, r7, c0, c1, 1	@ ID_PFR1
-	lsr	r7, #16
-	and	r7, #0xf
-	cmp	r7, #1
-	bne	1f
+	ubfx	r7, r7, #16, #4
+	teq	r7, #0
+	beq	1f
 	mrc	p15, 4, r7, c14, c1, 0	@ CNTHCTL
 	orr	r7, r7, #3		@ PL1PCEN | PL1PCTEN
 	mcr	p15, 4, r7, c14, c1, 0	@ CNTHCTL
-- 
2.7.4


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Re: [PATCH v2] ARM: virt: Relax arch timer version check during early boot

[Marc Zyngier]

On 2020-01-20 13:38, Vladimir Murzin wrote:
> Updates to the Generic Timer architecture allow ID_PFR1.GenTimer to
> have values other than 0 or 1 while still preserving backward
> compatibility. At the moment, Linux is quite strict in the way it
> handles this field at early boot and will not configure arch timer if
> it doesn't find the value 1.
> 
> Since here use ubfx for arch timer version extraction (hyb-stub build
> with -march=armv7-a, so it is safe)
> 
> To help backports (even though the code was correct at the time of 
> writing)
> Fixes: 8ec58be9f3ff ("ARM: virt: arch_timers: enable access to physical 
> timers")
> Signed-off-by: Vladimir Murzin <vladimir.murzin@arm.com>

Acked-by: Marc Zyngier <maz@kernel.org>

Feel free to put it into Russell's patch system.

Thanks,

         M.
-- 
Jazz is not dead. It just smells funny...

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Re: [PATCH v2] ARM: virt: Relax arch timer version check during early boot

[Vladimir Murzin]

On 1/20/20 2:01 PM, Marc Zyngier wrote:
> On 2020-01-20 13:38, Vladimir Murzin wrote:
>> Updates to the Generic Timer architecture allow ID_PFR1.GenTimer to
>> have values other than 0 or 1 while still preserving backward
>> compatibility. At the moment, Linux is quite strict in the way it
>> handles this field at early boot and will not configure arch timer if
>> it doesn't find the value 1.
>>
>> Since here use ubfx for arch timer version extraction (hyb-stub build
>> with -march=armv7-a, so it is safe)
>>
>> To help backports (even though the code was correct at the time of writing)
>> Fixes: 8ec58be9f3ff ("ARM: virt: arch_timers: enable access to physical timers")
>> Signed-off-by: Vladimir Murzin <vladimir.murzin@arm.com>
> 
> Acked-by: Marc Zyngier <maz@kernel.org>
> 
> Feel free to put it into Russell's patch system.

Patch has been accepted as patch 8955/1

Thanks!

Vladimir

> 
> Thanks,
> 
>         M.


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