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 13:53:26 +0100
From:   Julien Grall <julien.grall@....com>
To:     Oleksandr <olekstysh@...il.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 10/05/2019 13:27, Oleksandr wrote:
> 
> 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.

Xen does not offer another interface for SMP bring-up.

Cheers,

-- 
Julien Grall