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Re: [PATCH] ARM: owl: smp: Drop owl_secondary_boot()

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On 07/06/2017 10:39 AM, Mark Rutland wrote:
> On Thu, Jul 06, 2017 at 07:17:28PM +0200, Andreas Färber wrote:
>> Am 05.07.2017 um 04:36 schrieb Florian Fainelli:
>>> On July 4, 2017 4:32:18 PM PDT, "Andreas Färber" <afaerber@suse.de> wrote:
>>>> Commit 18cfd9429d8a82c49add8f3ca9d366599bfcac45 ("ARM: owl: smp: Drop
>>>> bogus holding pen") simplified the S500 SMP code by removing a loop for
>>>> pen_release in owl_secondary_boot(). Since then it is only calling
>>>> owl_v7_invalidate_l1() before branching to secondary_startup().
>>>>
>>>> The owl_v7_invalidate_l1() assembler function is superfluous, too.
>>>> Therefore drop owl_secondary_boot() and use secondary_boot() directly.
>>>>
>>>> Cc: David Liu <liuwei@actions-semi.com>
>>>> Signed-off-by: Andreas Färber <afaerber@suse.de>
>>>> ---
>>>
>>>> -	writel(virt_to_phys(owl_secondary_startup),
>>>> +	writel(virt_to_phys(secondary_startup),
>>>> 	       timer_base_addr + OWL_CPU1_ADDR + (cpu - 1) * 4);
>>>
>>> This is a kernel symbol so please use __pa_symbol() here, also you might want to build with CONFIG_DEBUG_VIRTUAL and see if you get other warnings about using virt_to_phys() in the owl platform code (I did not check if there are other uses)
>>
>> Thanks for the report. There are no other such uses in mach-actions, but
>> git-grep'ing for virt_to_phys in arch/arm/mach-* I spot at least one
>> other such usage in mach-oxnas:
>>
>> arch/arm/mach-oxnas/platsmp.c:
>> writel(virt_to_phys(ox820_secondary_startup),
>>
>> as well as this in mach-mvebu:
>>
>> arch/arm/mach-mvebu/platsmp.c:  writel(virt_to_phys(boot_addr), base +
>> MV98DX3236_CPU_RESUME_ADDR_REG);
>>
>> and these in mach-at91:
>>
>> arch/arm/mach-at91/pm.c:        pm_bu->canary = virt_to_phys(&canary);
>> arch/arm/mach-at91/pm.c:        pm_bu->resume = virt_to_phys(cpu_resume);
>>
>> What exactly is the difference between the two macros that makes it
>> wrong despite apparently working? 
> 
> virt_to_phys() is intended to operate on the linear/direct mapping of
> RAM.
> 
> __pa_symbol() is intended to operate on the kernel mapping, which may
> not be in the linear/direct mapping on all architectures. e.g. arm64 and
> x86_64 map the kernel image and RAM separately.
> 
> On 32-bit ARM the kernel image mapping is tied to the linear/direct
> mapping, so that works, but as it's semantically wrong (and broken for
> generic code), the DEBUG_VIRTUAL checks complain.
> 
>> In particular I am wondering whether
>> the SoC/board vendors in CC need to fix it in their 3.10 trees, too.
>>
>> In any case if this is a bug, I would rather fix it in a separate patch
>> for 4.13 and leave the name swap (this patch) for 4.14.
> 
> To the best of my knowledge there's no functional problem in this
> particular case, though it should be cleaned up so as to keep
> DEBUG_VRITUAL useful.

Exactly, it just happened to catch my eye while looking at this patch
series. I am wondering if there is a way we could check whether it makes
sense to use virt_to_phys() vs. __pa_symbol() at compile time and
produce an appropriate warning would that be the case. checkpatch.pl
would not be able to do this unless there is a prior build of the kernel
image, and a GCC plugin would not necessarily have global visibility
about other translation units either... hmmm.
-- 
Florian

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[PATCH] ARM: owl: smp: Drop owl_secondary_boot() Andreas Färber <afaerber@suse.de> - 2017-07-05 01:40 +0200
  Re: [PATCH] ARM: owl: smp: Drop owl_secondary_boot() Florian Fainelli <f.fainelli@gmail.com> - 2017-07-05 04:40 +0200
    Re: [PATCH] ARM: owl: smp: Drop owl_secondary_boot() Andreas Färber <afaerber@suse.de> - 2017-07-06 19:20 +0200
      Re: [PATCH] ARM: owl: smp: Drop owl_secondary_boot() Alexandre Belloni <alexandre.belloni@free-electrons.com> - 2017-07-06 19:40 +0200
        Re: [PATCH] ARM: owl: smp: Drop owl_secondary_boot() Florian Fainelli <f.fainelli@gmail.com> - 2017-07-06 21:50 +0200
          Re: [PATCH] ARM: owl: smp: Drop owl_secondary_boot() Gregory CLEMENT <gregory.clement@free-electrons.com> - 2017-07-07 09:40 +0200
            Re: [PATCH] ARM: owl: smp: Drop owl_secondary_boot() Florian Fainelli <f.fainelli@gmail.com> - 2017-07-07 19:40 +0200
      Re: [PATCH] ARM: owl: smp: Drop owl_secondary_boot() Mark Rutland <mark.rutland@arm.com> - 2017-07-06 19:50 +0200
        Re: [PATCH] ARM: owl: smp: Drop owl_secondary_boot() Florian Fainelli <f.fainelli@gmail.com> - 2017-07-06 23:20 +0200
      Re: [PATCH] ARM: owl: smp: Drop owl_secondary_boot() Andreas Färber <afaerber@suse.de> - 2017-07-10 00:00 +0200
        Re: [PATCH] ARM: owl: smp: Drop owl_secondary_boot() Florian Fainelli <f.fainelli@gmail.com> - 2017-07-10 06:30 +0200

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