linux-kernel - Re: [PATCH V2] ARM: mach-shmobile: Don't init CNTVOFF if PSCI is available

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Date:   Fri, 10 May 2019 15:27:50 +0300
From:   Oleksandr <olekstysh@...il.com>
To:     Julien Grall <julien.grall@....com>,
        linux-renesas-soc@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     horms@...ge.net.au, magnus.damm@...il.com, linux@...linux.org.uk,
        biju.das@...renesas.com,
        Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>
Subject: Re: [PATCH V2] ARM: mach-shmobile: Don't init CNTVOFF if PSCI is
 available


On 06.05.19 18:37, Julien Grall wrote:
> Hi Oleksandr,

Hi Julien


>> ---
>>   arch/arm/mach-shmobile/setup-rcar-gen2.c | 13 ++++++++++++-
>>   1 file changed, 12 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/arm/mach-shmobile/setup-rcar-gen2.c 
>> b/arch/arm/mach-shmobile/setup-rcar-gen2.c
>> index eea60b2..bc8537b 100644
>> --- a/arch/arm/mach-shmobile/setup-rcar-gen2.c
>> +++ b/arch/arm/mach-shmobile/setup-rcar-gen2.c
>> @@ -17,7 +17,9 @@
>>   #include <linux/of.h>
>>   #include <linux/of_fdt.h>
>>   #include <linux/of_platform.h>
>> +#include <xen/xen.h>
>>   #include <asm/mach/arch.h>
>> +#include <asm/psci.h>
>>   #include <asm/secure_cntvoff.h>
>>   #include "common.h"
>>   #include "rcar-gen2.h"
>> @@ -63,7 +65,16 @@ void __init rcar_gen2_timer_init(void)
>>       void __iomem *base;
>>       u32 freq;
>>   -    secure_cntvoff_init();
>> +    /*
>> +     * If PSCI is available then most likely we are running on 
>> PSCI-enabled
>> +     * U-Boot which, we assume, has already taken care of resetting 
>> CNTVOFF
>> +     * before switching to non-secure mode and we don't need to.
>> +     * Another check is to be sure that we are not running on top of 
>> Xen
>> +     * hypervisor, as CNTVOFF is controlled by hypervisor itself and
>> +     * shouldn't be touched by Dom0 in such case.
>
> If you are running on top of Xen, then PSCI will be available. So is 
> there any real value to check the presence of Xen as well?

I think, no. If the PSCI is a must to run Xen, then it is certainly an 
excessive check. I will drop it in V3.


>
> Cheers,
>
-- 
Regards,

Oleksandr Tyshchenko