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

[Marc Zyngier <maz@kernel.org>]

Hi Vladimir,

On 2020-01-20 11:46, Vladimir Murzin wrote:
> + Marc
> + kvmarm@lists.cs.columbia.edu
> 
> On 1/15/20 2:16 PM, Vladimir Murzin wrote:
>> Updates to the Generic Timer architecture allow ID_PFR1.GenTimer 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 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>

I'm not opposed to such a change, but it'd be good to document what 
other values
are expected here, as the current (Rev E_a) ARM ARM only mentions values 
0 and 1.

Thanks,

         M.

>> ---
>>  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
>> 

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