linux-kernel - Re: [PATCH] ARM: mach-shmobile: Don't configure ARCH timer if PSCI is enabled

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Message-ID: <e9ff61e3-620f-b794-824d-39ab70707e63@gmail.com>
Date:   Thu, 18 Apr 2019 13:35:14 +0300
From:   Oleksandr <olekstysh@...il.com>
To:     Biju Das <biju.das@...renesas.com>,
        "linux-renesas-soc@...r.kernel.org" 
        <linux-renesas-soc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Cc:     "julien.grall@....com" <julien.grall@....com>,
        "horms@...ge.net.au" <horms@...ge.net.au>,
        "magnus.damm@...il.com" <magnus.damm@...il.com>,
        "linux@...linux.org.uk" <linux@...linux.org.uk>,
        Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>
Subject: Re: [PATCH] ARM: mach-shmobile: Don't configure ARCH timer if PSCI is
 enabled


On 18.04.19 10:14, Biju Das wrote:
> Hi Oleksandr,

Hi Biju

>
> Thanks for the patch.
>
>> Subject: [PATCH] ARM: mach-shmobile: Don't configure ARCH timer if PSCI is
>> enabled
>>
>> From: Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>
>>
>> If CONFIG_PSCI is enabled then most likely we are running on PSCI-enabled
>> U-Boot which, we assume, has already taken care of configuring ARCH timer
>> stuff before switching to non-secure mode.
>>
>> Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>
>>
>> ---
>> A bit of context here...
>>
>> We are highly interested in Renesas "Stout" board support (r8a7790) in Xen
>> hypervisor. The reason is to have fully supported HW for performing
>> "OSSTEST" (Xen automatic test system) on ARM32.
>>
>> To reach that target we need a "generic way" for the secondary CPU cores
>> bring up and switching them to non-secure hyp mode.
>> So, the PSCI as a generic well-known way to bring up CPUs, was chosen for
>> that purpose.
>>
>> You can find corresponding patches for U-Boot here:
>> http://u-boot.10912.n7.nabble.com/PATCH-0-3-PSCI-support-for-r8a7790-
>> SoC-Lager-Stout-boards-td357352.html
>>
>> You can find corresponding patches for Xen hypervisor here:
>> https://www.mail-archive.com/xen-
>> devel@...ts.xenproject.org/msg43332.html
>>
>> To sumarize:
>> Together with enabling CONFIG_PSCI in shmobile_defconfig, current patch is
>> a minimal required change needed to run mainline Linux on top of PSCI-
>> enabled U-Boot.
>> There is no need to modify device tree. U-Boot will take care of inserting
>> proper "enable-method" strings in CPU nodes.
>>
>> ---
>>   arch/arm/mach-shmobile/setup-rcar-gen2.c | 9 ++++++++-
>>   1 file changed, 8 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..bac4490 100644
>> --- a/arch/arm/mach-shmobile/setup-rcar-gen2.c
>> +++ b/arch/arm/mach-shmobile/setup-rcar-gen2.c
>> @@ -32,7 +32,7 @@ static const struct of_device_id cpg_matches[]
>> __initconst = {
>>   	{ /* sentinel */ }
>>   };
>>
>> -static unsigned int __init get_extal_freq(void)
>> +static unsigned int __init __maybe_unused get_extal_freq(void)
>>   {
>>   	const struct of_device_id *match;
>>   	struct device_node *cpg, *extal;
>> @@ -60,6 +60,12 @@ static unsigned int __init get_extal_freq(void)
>>
>>   void __init rcar_gen2_timer_init(void)
>>   {
>> +/*
>> + * If CONFIG_PSCI is enabled then most likely we are running on
>> +PSCI-enabled
>> + * U-Boot which, we assume, has already taken care of configuring ARCH
>> +timer
>> + * stuff before switching to non-secure mode.
>> + */
>> +#if !defined(CONFIG_ARM_PSCI)
> Is it required?  If you see the below comment, it is already taken care
> by the below code.
>
> Is your code entering into this block, when booting  the kernel in NS mode?

No, the code below seems to do the proper things. If arch timer is 
configured in U-Boot (enabled and programmed with correct freq) then

that code doesn't try to update it.

But "#if !defined(CONFIG_ARM_PSCI)" wraps secure_cntvoff_init() call as 
well, which resets CNTVOFF,

and this is something I tried to avoid the first from being executed on 
a CPU, which is in SVC mode (when running on top of Xen).


I was thinking whether I should wrap arch timer updating procedure as 
well and decided to do so, but probably I shouldn't have.

>
> <snip>
>    /*
>   87          * Update the timer if it is either not running, or is not at the
>   88          * right frequency. The timer is only configurable in secure mode
>   89          * so this avoids an abort if the loader started the timer and
>   90          * entered the kernel in non-secure mode.
>   91          */
>   92
>   93         if ((ioread32(base + CNTCR) & 1) == 0 ||
>   94             ioread32(base + CNTFID0) != freq) {
>   95                 /* Update registers with correct frequency */
>   96                 iowrite32(freq, base + CNTFID0);
>   97                 asm volatile("mcr p15, 0, %0, c14, c0, 0" : : "r" (freq));
>   98
>   99                 /* make sure arch timer is started by setting bit 0 of CNTCR */
> 100                 iowrite32(1, base + CNTCR);
> 101         }
>
>
> Regards,
> Biju
>
>>   	void __iomem *base;
>>   	u32 freq;
>>
>> @@ -101,6 +107,7 @@ void __init rcar_gen2_timer_init(void)
>>   	}
>>
>>   	iounmap(base);
>> +#endif /* #if !defined(CONFIG_ARM_PSCI) */
>>
>>   	of_clk_init(NULL);
>>   	timer_probe();
>> --
>> 2.7.4

-- 
Regards,

Oleksandr Tyshchenko