linux-kernel - Re: [PATCH 1/1] ARM: pxa168: fix corrected reset vector

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Message-ID: <AANLkTikUEav5Jo9rCFw7hTs8U3anpDZhSF_jtGKKMma7@mail.gmail.com>
Date:	Tue, 31 Aug 2010 15:27:48 +0800
From:	Eric Miao <eric.y.miao@...il.com>
To:	Haojian Zhuang <haojian.zhuang@...il.com>
Cc:	"Mark F. Brown" <mark.brown314@...il.com>,
	Haojian Zhuang <haojian.zhuang@...vell.com>,
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/1] ARM: pxa168: fix corrected reset vector

On Tue, Aug 31, 2010 at 3:21 PM, Haojian Zhuang
<haojian.zhuang@...il.com> wrote:
> On Tue, Aug 31, 2010 at 3:08 PM, Eric Miao <eric.y.miao@...il.com> wrote:
>> On Tue, Aug 31, 2010 at 3:02 PM, Haojian Zhuang
>> <haojian.zhuang@...il.com> wrote:
>>> On Tue, Aug 31, 2010 at 2:48 PM, Mark F. Brown <mark.brown314@...il.com> wrote:
>>>> On Tue, Aug 31, 2010 at 2:26 AM, Haojian Zhuang
>>>> <haojian.zhuang@...il.com> wrote:
>>>>> On Tue, Aug 31, 2010 at 2:08 PM, Eric Miao <eric.y.miao@...il.com> wrote:
>>>>>> On Tue, Aug 31, 2010 at 2:04 PM, Eric Miao <eric.y.miao@...il.com> wrote:
>>>>>>> On Tue, Aug 31, 2010 at 2:02 PM, Mark F. Brown <mark.brown314@...il.com> wrote:
>>>>>>>> On Tue, Aug 31, 2010 at 1:48 AM, Eric Miao <eric.y.miao@...il.com> wrote:
>>>>>>>>> On Thu, Aug 26, 2010 at 5:07 PM, Mark F. Brown <mark.brown314@...il.com> wrote:
>>>>>>>>>> Signed-off-by: Mark F. Brown <mark.brown314@...il.com>
>>>>>>>>>> ---
>>>>>>>>>>  arch/arm/mach-mmp/include/mach/system.h |    2 +-
>>>>>>>>>>  1 files changed, 1 insertions(+), 1 deletions(-)
>>>>>>>>>>
>>>>>>>>>> diff --git a/arch/arm/mach-mmp/include/mach/system.h b/arch/arm/mach-mmp/include/mach/system.h
>>>>>>>>>> index 4f5b0e0..926e9c0 100644
>>>>>>>>>> --- a/arch/arm/mach-mmp/include/mach/system.h
>>>>>>>>>> +++ b/arch/arm/mach-mmp/include/mach/system.h
>>>>>>>>>> @@ -16,6 +16,6 @@ static inline void arch_idle(void)
>>>>>>>>>>
>>>>>>>>>>  static inline void arch_reset(char mode, const char *cmd)
>>>>>>>>>>  {
>>>>>>>>>> -       cpu_reset(0);
>>>>>>>>>> +       cpu_reset(0xffff0000);
>>>>>>>>>
>>>>>>>>> Not sure if this correct. But normally reset jump happens after we turn
>>>>>>>>> off the MMU and so on. Ain't the BootROM starts from 0 ?
>>>>>>>>>
>>>>>>>>>>  }
>>>>>>>>>>  #endif /* __ASM_MACH_SYSTEM_H */
>>>>>>>>>> --
>>>>>>>>>> 1.7.0.4
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>
>>>>>>>> Eric, the boot-rom for pxa168 starts at 0xffff_0000. I am pretty sure
>>>>>>>> about that! If you set the reset vector to 0x0 it will crash during
>>>>>>>> reboot. I will send you xdb snapshots if you need me to.
>>>>>>>>
>>>>>>>
>>>>>>> OK, you are expert on this :-)
>>>>>>>
>>>>>>> Applied to 'fix'.
>>>>>>>
>>>>>>
>>>>>> One moment. Since this is really global to pxa910 and mmp2, so I
>>>>>> suggest this being fixed for pxa168 only first. How about this:
>>>>>>
>>>>>>    ARM: pxa168: fix corrected reset vector
>>>>>>
>>>>>>    Reset vector for pxa168 is 0xffff_0000 not 0x0. This fix allows
>>>>>>    reboot to work
>>>>>>
>>>>>>    Signed-off-by: Mark F. Brown <mark.brown314@...il.com>
>>>>>>
>>>>>> diff --git a/arch/arm/mach-mmp/include/mach/system.h
>>>>>> b/arch/arm/mach-mmp/include/mach/system.h
>>>>>> index 4f5b0e0..1a8a25e 100644
>>>>>> --- a/arch/arm/mach-mmp/include/mach/system.h
>>>>>> +++ b/arch/arm/mach-mmp/include/mach/system.h
>>>>>> @@ -9,6 +9,8 @@
>>>>>>  #ifndef __ASM_MACH_SYSTEM_H
>>>>>>  #define __ASM_MACH_SYSTEM_H
>>>>>>
>>>>>> +#include <mach/cputype.h>
>>>>>> +
>>>>>>  static inline void arch_idle(void)
>>>>>>  {
>>>>>>        cpu_do_idle();
>>>>>> @@ -16,6 +18,9 @@ static inline void arch_idle(void)
>>>>>>
>>>>>>  static inline void arch_reset(char mode, const char *cmd)
>>>>>>  {
>>>>>> -       cpu_reset(0);
>>>>>> +       if (cpu_is_pxa168())
>>>>>> +               cpu_reset(0xffff0000);
>>>>>> +       else
>>>>>> +               cpu_reset(0);
>>>>>>  }
>>>>>>  #endif /* __ASM_MACH_SYSTEM_H */
>>>>>> --
>>>>>> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
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>>>>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>>>>> Please read the FAQ at  http://www.tux.org/lkml/
>>>>>>
>>>>> The reset code is in below.
>>>>>
>>>>>        .align  5
>>>>> ENTRY(cpu_mohawk_reset)
>>>>>        mov     ip, #0
>>>>>        mcr     p15, 0, ip, c7, c7, 0           @ invalidate I,D caches
>>>>>        mcr     p15, 0, ip, c7, c10, 4          @ drain WB
>>>>>        mcr     p15, 0, ip, c8, c7, 0           @ invalidate I & D TLBs
>>>>>        mrc     p15, 0, ip, c1, c0, 0           @ ctrl register
>>>>>        bic     ip, ip, #0x0007                 @ .............cam
>>>>>        bic     ip, ip, #0x1100                 @ ...i...s........
>>>>>        mcr     p15, 0, ip, c1, c0, 0           @ ctrl register
>>>>>        mov     pc, r0
>>>>>
>>>>> MMU is disabled at here and replace PC with r0 value. I doubt code
>>>>> executed correctly at here. While MMU is disabled, the PC should be
>>>>> continue in the range of 0xCxxx_xxxx (kernel space). "mov pc, r0"
>>>>> shouldn't be executed. Instruction fetch failure should occurs since
>>>>> there's no physical address in 0xCxxx_xxxx.
>>>>>
>>>>> Correct me if I'm wrong.
>>>>>
>>>>> Thanks
>>>>> Haojian
>>>>>
>>>>
>>>> Haojian,
>>>>
>>>> I think there is a pipeline execution of the mov pc, r0 instruction.
>>>> If I remember correctly you need to do a similar jump when you turn
>>>> the MMU on in early boot code. If it makes any difference I did test
>>>> this code on pxa168 before submitting it. I will double check the mmp2
>>>> and the pxa910 reset vectors with the Boot ROM developers.
>>>>
>>>
>>> In early boot code, 1:1 (physical:virtual) mapping is used. It means
>>> that physical address is same as virtual address. So you can operature
>>> mmu as you wish.
>>>
>>> By the way, I don't suggest to reset CPU by this way. Reset is not
>>> only make code running from the head, it should also clear registers
>>> and RTL logic in CPU.
>>>
>>
>> Depends on if pxa168 has a reset signal asserted from internal or from
>> external GPIO, which is controllable from the CPU itself. That's what
>> pxa is doing at this moment.
>>
>
> Yes, it depends on reset signal. Watchdog timer is built in pxa168. So
> I think that watchdog reset could be better.
>

Haojian, note we have a reboot mode, so possibly will have to implement
all of them if capable.
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