[Qemu-devel] [Bug 608107] [NEW] ppc fails to clear MSR_POW when incurring exception

[Qemu-devel] [Bug 608107] [NEW] ppc fails to clear MSR_POW when incurring exception

[till]

Public bug reported:

QEMU VERSION: 0.12.4

According to FreeScale's 'Programming Environments Manual for 32-bit Implementations of the PowerPC Architecture' [MPCFPE32B, Rev.3, 9/2005], section 6.5, table 6-7, an interrupt resets MSR_POW to zero but qemu-0.12.4 fails to do so.
Resetting the bit is necessary in order to bring the processor out of power-management since otherwise it goes to sleep right away in the exception handler, i.e., it is impossible to leave PM-mode.

** Affects: qemu
     Importance: Undecided
         Status: New

-- 
ppc fails to clear MSR_POW when incurring exception
https://bugs.launchpad.net/bugs/608107
You received this bug notification because you are a member of qemu-
devel-ml, which is subscribed to QEMU.

Status in QEMU: New

Bug description:
QEMU VERSION: 0.12.4

According to FreeScale's 'Programming Environments Manual for 32-bit Implementations of the PowerPC Architecture' [MPCFPE32B, Rev.3, 9/2005], section 6.5, table 6-7, an interrupt resets MSR_POW to zero but qemu-0.12.4 fails to do so.
Resetting the bit is necessary in order to bring the processor out of power-management since otherwise it goes to sleep right away in the exception handler, i.e., it is impossible to leave PM-mode.

[Qemu-devel] [Bug 608107] Re: ppc fails to clear MSR_POW when incurring exception

[till]

** Patch added: "Suggested fix"
   http://launchpadlibrarian.net/52250654/ppc-msr_pow-clear.diff

-- 
ppc fails to clear MSR_POW when incurring exception
https://bugs.launchpad.net/bugs/608107
You received this bug notification because you are a member of qemu-
devel-ml, which is subscribed to QEMU.

Status in QEMU: New

Bug description:
QEMU VERSION: 0.12.4

According to FreeScale's 'Programming Environments Manual for 32-bit Implementations of the PowerPC Architecture' [MPCFPE32B, Rev.3, 9/2005], section 6.5, table 6-7, an interrupt resets MSR_POW to zero but qemu-0.12.4 fails to do so.
Resetting the bit is necessary in order to bring the processor out of power-management since otherwise it goes to sleep right away in the exception handler, i.e., it is impossible to leave PM-mode.

[Qemu-devel] [Bug 608107] Re: ppc fails to clear MSR_POW when incurring exception

[Thomas Monjalon]

** Changed in: qemu
       Status: New => Confirmed

-- 
ppc fails to clear MSR_POW when incurring exception
https://bugs.launchpad.net/bugs/608107
You received this bug notification because you are a member of qemu-
devel-ml, which is subscribed to QEMU.

Status in QEMU: Confirmed

Bug description:
QEMU VERSION: 0.12.4

According to FreeScale's 'Programming Environments Manual for 32-bit Implementations of the PowerPC Architecture' [MPCFPE32B, Rev.3, 9/2005], section 6.5, table 6-7, an interrupt resets MSR_POW to zero but qemu-0.12.4 fails to do so.
Resetting the bit is necessary in order to bring the processor out of power-management since otherwise it goes to sleep right away in the exception handler, i.e., it is impossible to leave PM-mode.

[Qemu-devel] [PATCH] target-ppc: clear MSR_POW on interrupt

[Thomas Monjalon]

From: till <608107@bugs.launchpad.net>

According to FreeScale's 'Programming Environments Manual for 32-bit
Implementations of the PowerPC Architecture' [MPCFPE32B, Rev.3, 9/2005],
section 6.5, table 6-7, an interrupt resets MSR_POW to zero but qemu-0.12.4
fails to do so.
Resetting the bit is necessary in order to bring the processor out of power
management since otherwise it goes to sleep right away in the exception
handler, i.e., it is impossible to leave PM-mode.

https://bugs.launchpad.net/qemu/+bug/608107

Signed-off-by: till <608107@bugs.launchpad.net>
Acked-by: Thomas Monjalon <thomas@monjalon.net>

---
 target-ppc/helper.c |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)

diff --git a/target-ppc/helper.c b/target-ppc/helper.c
index f66fb30..0bb353e 100644
--- a/target-ppc/helper.c
+++ b/target-ppc/helper.c
@@ -2578,6 +2578,7 @@ static inline void powerpc_excp(CPUState *env, int excp_model, int excp)
     if (new_msr & ((1 << MSR_IR) | (1 << MSR_DR)))
         tlb_flush(env, 1);
     /* reload MSR with correct bits */
+    new_msr &= ~((target_ulong)1 << MSR_POW);
     new_msr &= ~((target_ulong)1 << MSR_EE);
     new_msr &= ~((target_ulong)1 << MSR_PR);
     new_msr &= ~((target_ulong)1 << MSR_FP);

Re: [Qemu-devel] [PATCH] target-ppc: clear MSR_POW on interrupt

[Alexander Graf]

Thomas Monjalon wrote:
> From: till <608107@bugs.launchpad.net>
>
> According to FreeScale's 'Programming Environments Manual for 32-bit
> Implementations of the PowerPC Architecture' [MPCFPE32B, Rev.3, 9/2005],
> section 6.5, table 6-7, an interrupt resets MSR_POW to zero but qemu-0.12.4
> fails to do so.
> Resetting the bit is necessary in order to bring the processor out of power
> management since otherwise it goes to sleep right away in the exception
> handler, i.e., it is impossible to leave PM-mode.
>   

This doesn't look right. POW shouldn't even get stored in SRR1. Could
you please redo the patch and make sure that mtmsr masks out MSR_POW?


Alex

Re: [Qemu-devel] [PATCH] target-ppc: clear MSR_POW on interrupt

[Thomas Monjalon]

Alexander Graf wrote:
> Thomas Monjalon wrote:
> > From: till <608107@bugs.launchpad.net>
> > 
> > According to FreeScale's 'Programming Environments Manual for 32-bit
> > Implementations of the PowerPC Architecture' [MPCFPE32B, Rev.3, 9/2005],
> > section 6.5, table 6-7, an interrupt resets MSR_POW to zero but
> > qemu-0.12.4 fails to do so.
> > Resetting the bit is necessary in order to bring the processor out of
> > power management since otherwise it goes to sleep right away in the
> > exception handler, i.e., it is impossible to leave PM-mode.
> 
> This doesn't look right. POW shouldn't even get stored in SRR1. Could
> you please redo the patch and make sure that mtmsr masks out MSR_POW?

Could you point sections of the specification for these requirements ?

I think SRR1 can save any bits. Non significant bits can be overriden and are 
masked out when RFI occurs.

-- 
Thomas

Re: [Qemu-devel] [PATCH] target-ppc: clear MSR_POW on interrupt

[Alexander Graf]

Thomas Monjalon wrote:
> Alexander Graf wrote:
>   
>> Thomas Monjalon wrote:
>>     
>>> From: till <608107@bugs.launchpad.net>
>>>
>>> According to FreeScale's 'Programming Environments Manual for 32-bit
>>> Implementations of the PowerPC Architecture' [MPCFPE32B, Rev.3, 9/2005],
>>> section 6.5, table 6-7, an interrupt resets MSR_POW to zero but
>>> qemu-0.12.4 fails to do so.
>>> Resetting the bit is necessary in order to bring the processor out of
>>> power management since otherwise it goes to sleep right away in the
>>> exception handler, i.e., it is impossible to leave PM-mode.
>>>       
>> This doesn't look right. POW shouldn't even get stored in SRR1. Could
>> you please redo the patch and make sure that mtmsr masks out MSR_POW?
>>     
>
> Could you point sections of the specification for these requirements ?
>
> I think SRR1 can save any bits. Non significant bits can be overriden and are 
> masked out when RFI occurs.
>   

I'm not saying I'm 100% sure on this, but take a look at the e300
reference manual
(http://cache.freescale.com/files/32bit/doc/ref_manual/e300coreRM.pdf)
section 5.2.3. POW is bit 13 in this notion. I don't see it getting
saved to SRR1.


Alex

Re: [Qemu-devel] [PATCH] target-ppc: clear MSR_POW on interrupt

[Thomas Monjalon]

Alexander Graf wrote:
> Thomas Monjalon wrote:
> > Alexander Graf wrote:
> >> Thomas Monjalon wrote:
> >>> From: till <608107@bugs.launchpad.net>
> >>> 
> >>> According to FreeScale's 'Programming Environments Manual for 32-bit
> >>> Implementations of the PowerPC Architecture' [MPCFPE32B, Rev.3,
> >>> 9/2005], section 6.5, table 6-7, an interrupt resets MSR_POW to zero
> >>> but qemu-0.12.4 fails to do so.
> >>> Resetting the bit is necessary in order to bring the processor out of
> >>> power management since otherwise it goes to sleep right away in the
> >>> exception handler, i.e., it is impossible to leave PM-mode.
> >> 
> >> This doesn't look right. POW shouldn't even get stored in SRR1. Could
> >> you please redo the patch and make sure that mtmsr masks out MSR_POW?
> > 
> > Could you point sections of the specification for these requirements ?
> > 
> > I think SRR1 can save any bits. Non significant bits can be overriden and
> > are masked out when RFI occurs.
> 
> I'm not saying I'm 100% sure on this, but take a look at the e300
> reference manual
> (http://cache.freescale.com/files/32bit/doc/ref_manual/e300coreRM.pdf)
> section 5.2.3. POW is bit 13 in this notion. I don't see it getting
> saved to SRR1.

The current implementation (commit c3d420e) save all the bits and restore only 
the needed ones (excluding POW). So POW is cleared after an interrupt.

But the subject of this patch wasn't on saved bits. It is to clear POW in the 
interrupt context. For an unknown reason, it's not done and it's clearly a bug 
to fix.

-- 
Thomas

Re: [Qemu-devel] [PATCH] target-ppc: clear MSR_POW on interrupt

[Alexander Graf]

Thomas Monjalon wrote:
> Alexander Graf wrote:
>   
>> Thomas Monjalon wrote:
>>     
>>> Alexander Graf wrote:
>>>       
>>>> Thomas Monjalon wrote:
>>>>         
>>>>> From: till <608107@bugs.launchpad.net>
>>>>>
>>>>> According to FreeScale's 'Programming Environments Manual for 32-bit
>>>>> Implementations of the PowerPC Architecture' [MPCFPE32B, Rev.3,
>>>>> 9/2005], section 6.5, table 6-7, an interrupt resets MSR_POW to zero
>>>>> but qemu-0.12.4 fails to do so.
>>>>> Resetting the bit is necessary in order to bring the processor out of
>>>>> power management since otherwise it goes to sleep right away in the
>>>>> exception handler, i.e., it is impossible to leave PM-mode.
>>>>>           
>>>> This doesn't look right. POW shouldn't even get stored in SRR1. Could
>>>> you please redo the patch and make sure that mtmsr masks out MSR_POW?
>>>>         
>>> Could you point sections of the specification for these requirements ?
>>>
>>> I think SRR1 can save any bits. Non significant bits can be overriden and
>>> are masked out when RFI occurs.
>>>       
>> I'm not saying I'm 100% sure on this, but take a look at the e300
>> reference manual
>> (http://cache.freescale.com/files/32bit/doc/ref_manual/e300coreRM.pdf)
>> section 5.2.3. POW is bit 13 in this notion. I don't see it getting
>> saved to SRR1.
>>     
>
> The current implementation (commit c3d420e) save all the bits and restore only 
> the needed ones (excluding POW). So POW is cleared after an interrupt.
>
> But the subject of this patch wasn't on saved bits. It is to clear POW in the 
> interrupt context. For an unknown reason, it's not done and it's clearly a bug 
> to fix.
>   

I completely agree. In fact, the mere fact that a bit can slip through
this loop indicates that something goes wrong.

As far as SRR1 goes, PowerISA 2.06 draws an even more complicated
picture: Page 816 says that SRR1 bits 42:44 indicate the power save exit
reason while 46:47 indicate how much state was transferred. Bit 45 would
be MSR_POW which is defined as "set to 0".

Because that means that we'll have to set MSR_POW in to 0 in SRR1 and
the interrupt switching function, we can just set it to 0 on mtmsr. That
was my point :).


Alex

Re: [Qemu-devel] [PATCH] target-ppc: clear MSR_POW on interrupt

[Edgar E. Iglesias]

On Fri, Sep 10, 2010 at 05:50:27PM +0200, Alexander Graf wrote:
> Thomas Monjalon wrote:
> > Alexander Graf wrote:
> >   
> >> Thomas Monjalon wrote:
> >>     
> >>> Alexander Graf wrote:
> >>>       
> >>>> Thomas Monjalon wrote:
> >>>>         
> >>>>> From: till <608107@bugs.launchpad.net>
> >>>>>
> >>>>> According to FreeScale's 'Programming Environments Manual for 32-bit
> >>>>> Implementations of the PowerPC Architecture' [MPCFPE32B, Rev.3,
> >>>>> 9/2005], section 6.5, table 6-7, an interrupt resets MSR_POW to zero
> >>>>> but qemu-0.12.4 fails to do so.
> >>>>> Resetting the bit is necessary in order to bring the processor out of
> >>>>> power management since otherwise it goes to sleep right away in the
> >>>>> exception handler, i.e., it is impossible to leave PM-mode.
> >>>>>           
> >>>> This doesn't look right. POW shouldn't even get stored in SRR1. Could
> >>>> you please redo the patch and make sure that mtmsr masks out MSR_POW?
> >>>>         
> >>> Could you point sections of the specification for these requirements ?
> >>>
> >>> I think SRR1 can save any bits. Non significant bits can be overriden and
> >>> are masked out when RFI occurs.
> >>>       
> >> I'm not saying I'm 100% sure on this, but take a look at the e300
> >> reference manual
> >> (http://cache.freescale.com/files/32bit/doc/ref_manual/e300coreRM.pdf)
> >> section 5.2.3. POW is bit 13 in this notion. I don't see it getting
> >> saved to SRR1.
> >>     
> >
> > The current implementation (commit c3d420e) save all the bits and restore only 
> > the needed ones (excluding POW). So POW is cleared after an interrupt.
> >
> > But the subject of this patch wasn't on saved bits. It is to clear POW in the 
> > interrupt context. For an unknown reason, it's not done and it's clearly a bug 
> > to fix.
> >   
> 
> I completely agree. In fact, the mere fact that a bit can slip through
> this loop indicates that something goes wrong.
> 
> As far as SRR1 goes, PowerISA 2.06 draws an even more complicated
> picture: Page 816 says that SRR1 bits 42:44 indicate the power save exit
> reason while 46:47 indicate how much state was transferred. Bit 45 would
> be MSR_POW which is defined as "set to 0".
> 
> Because that means that we'll have to set MSR_POW in to 0 in SRR1 and
> the interrupt switching function, we can just set it to 0 on mtmsr. That
> was my point :).

Hi,

I'm not very familiar with PPC but the way I interpret it, we should clear
the POW bit in both MSR and SRR1 when the interrupt waking the CPU is
taken. While the CPU is sleeping, the POW bit should remain set in MSR
though.

As Alex comments, the submited patch fails to make sure the SRR1 bit
13 is cleared when taking the interrupt, but I don't think clearing
MSR[POW] in mtmsr is the right thing. In practice it probably doesn't
matter much, possibly a bit annoying if you inspect the sleeping state
from a debugger or similar.

I think mtmsr should set MSR[POW] and powerpc_excp() should clear
MSR[POW] prior to copying MSR into SRR1.

Not sure, but thats the way I interpret it...

Cheers

Re: [Qemu-devel] [PATCH] target-ppc: clear MSR_POW on interrupt

[Alexander Graf]

Am 10.09.2010 um 18:08 schrieb "Edgar E. Iglesias" <edgar.iglesias@gmail.com>:

> On Fri, Sep 10, 2010 at 05:50:27PM +0200, Alexander Graf wrote:
>> Thomas Monjalon wrote:
>>> Alexander Graf wrote:
>>> 
>>>> Thomas Monjalon wrote:
>>>> 
>>>>> Alexander Graf wrote:
>>>>> 
>>>>>> Thomas Monjalon wrote:
>>>>>> 
>>>>>>> From: till <608107@bugs.launchpad.net>
>>>>>>> 
>>>>>>> According to FreeScale's 'Programming Environments Manual for 32-bit
>>>>>>> Implementations of the PowerPC Architecture' [MPCFPE32B, Rev.3,
>>>>>>> 9/2005], section 6.5, table 6-7, an interrupt resets MSR_POW to zero
>>>>>>> but qemu-0.12.4 fails to do so.
>>>>>>> Resetting the bit is necessary in order to bring the processor out of
>>>>>>> power management since otherwise it goes to sleep right away in the
>>>>>>> exception handler, i.e., it is impossible to leave PM-mode.
>>>>>>> 
>>>>>> This doesn't look right. POW shouldn't even get stored in SRR1. Could
>>>>>> you please redo the patch and make sure that mtmsr masks out MSR_POW?
>>>>>> 
>>>>> Could you point sections of the specification for these requirements ?
>>>>> 
>>>>> I think SRR1 can save any bits. Non significant bits can be overriden and
>>>>> are masked out when RFI occurs.
>>>>> 
>>>> I'm not saying I'm 100% sure on this, but take a look at the e300
>>>> reference manual
>>>> (http://cache.freescale.com/files/32bit/doc/ref_manual/e300coreRM.pdf)
>>>> section 5.2.3. POW is bit 13 in this notion. I don't see it getting
>>>> saved to SRR1.
>>>> 
>>> 
>>> The current implementation (commit c3d420e) save all the bits and restore only 
>>> the needed ones (excluding POW). So POW is cleared after an interrupt.
>>> 
>>> But the subject of this patch wasn't on saved bits. It is to clear POW in the 
>>> interrupt context. For an unknown reason, it's not done and it's clearly a bug 
>>> to fix.
>>> 
>> 
>> I completely agree. In fact, the mere fact that a bit can slip through
>> this loop indicates that something goes wrong.
>> 
>> As far as SRR1 goes, PowerISA 2.06 draws an even more complicated
>> picture: Page 816 says that SRR1 bits 42:44 indicate the power save exit
>> reason while 46:47 indicate how much state was transferred. Bit 45 would
>> be MSR_POW which is defined as "set to 0".
>> 
>> Because that means that we'll have to set MSR_POW in to 0 in SRR1 and
>> the interrupt switching function, we can just set it to 0 on mtmsr. That
>> was my point :).
> 
> Hi,
> 
> I'm not very familiar with PPC but the way I interpret it, we should clear
> the POW bit in both MSR and SRR1 when the interrupt waking the CPU is
> taken. While the CPU is sleeping, the POW bit should remain set in MSR
> though.
> 
> As Alex comments, the submited patch fails to make sure the SRR1 bit
> 13 is cleared when taking the interrupt, but I don't think clearing
> MSR[POW] in mtmsr is the right thing. In practice it probably doesn't
> matter much, possibly a bit annoying if you inspect the sleeping state
> from a debugger or similar.
> 
> I think mtmsr should set MSR[POW] and powerpc_excp() should clear
> MSR[POW] prior to copying MSR into SRR1.
> 
> Not sure, but thats the way I interpret it...

Agreed.

Alex

> 

Re: [Qemu-devel] [PATCH] target-ppc: clear MSR_POW on interrupt

[Thomas Monjalon]

Alexander Graf wrote:
> Am 10.09.2010 um 18:08 schrieb "Edgar E. Iglesias" 
<edgar.iglesias@gmail.com>:
> > On Fri, Sep 10, 2010 at 05:50:27PM +0200, Alexander Graf wrote:
> >> Thomas Monjalon wrote:
> >>> Alexander Graf wrote:
> >>>> Thomas Monjalon wrote:
> >>>>> Alexander Graf wrote:
> >>>>>> Thomas Monjalon wrote:
> >>>>>>> From: till <608107@bugs.launchpad.net>
> >>>>>>> 
> >>>>>>> According to FreeScale's 'Programming Environments Manual for
> >>>>>>> 32-bit Implementations of the PowerPC Architecture' [MPCFPE32B,
> >>>>>>> Rev.3, 9/2005], section 6.5, table 6-7, an interrupt resets
> >>>>>>> MSR_POW to zero but qemu-0.12.4 fails to do so.
> >>>>>>> Resetting the bit is necessary in order to bring the processor out
> >>>>>>> of power management since otherwise it goes to sleep right away in
> >>>>>>> the exception handler, i.e., it is impossible to leave PM-mode.
> >>>>>> 
> >>>>>> This doesn't look right. POW shouldn't even get stored in SRR1.
> >>>>>> Could you please redo the patch and make sure that mtmsr masks out
> >>>>>> MSR_POW?
> >>>>> 
> >>>>> Could you point sections of the specification for these requirements
> >>>>> ?
> >>>>> 
> >>>>> I think SRR1 can save any bits. Non significant bits can be overriden
> >>>>> and are masked out when RFI occurs.
> >>>> 
> >>>> I'm not saying I'm 100% sure on this, but take a look at the e300
> >>>> reference manual
> >>>> (http://cache.freescale.com/files/32bit/doc/ref_manual/e300coreRM.pdf)
> >>>> section 5.2.3. POW is bit 13 in this notion. I don't see it getting
> >>>> saved to SRR1.
> >>> 
> >>> The current implementation (commit c3d420e) save all the bits and
> >>> restore only the needed ones (excluding POW). So POW is cleared after
> >>> an interrupt.
> >>> 
> >>> But the subject of this patch wasn't on saved bits. It is to clear POW
> >>> in the interrupt context. For an unknown reason, it's not done and
> >>> it's clearly a bug to fix.
> >> 
> >> I completely agree. In fact, the mere fact that a bit can slip through
> >> this loop indicates that something goes wrong.
> >> 
> >> As far as SRR1 goes, PowerISA 2.06 draws an even more complicated
> >> picture: Page 816 says that SRR1 bits 42:44 indicate the power save exit
> >> reason while 46:47 indicate how much state was transferred. Bit 45 would
> >> be MSR_POW which is defined as "set to 0".
> >> 
> >> Because that means that we'll have to set MSR_POW in to 0 in SRR1 and
> >> the interrupt switching function, we can just set it to 0 on mtmsr. That
> >> was my point :).
> > 
> > Hi,
> > 
> > I'm not very familiar with PPC but the way I interpret it, we should
> > clear the POW bit in both MSR and SRR1 when the interrupt waking the CPU
> > is taken. While the CPU is sleeping, the POW bit should remain set in
> > MSR though.
> > 
> > As Alex comments, the submited patch fails to make sure the SRR1 bit
> > 13 is cleared when taking the interrupt, but I don't think clearing
> > MSR[POW] in mtmsr is the right thing. In practice it probably doesn't
> > matter much, possibly a bit annoying if you inspect the sleeping state
> > from a debugger or similar.
> > 
> > I think mtmsr should set MSR[POW] and powerpc_excp() should clear
> > MSR[POW] prior to copying MSR into SRR1.
> > 
> > Not sure, but thats the way I interpret it...
> 
> Agreed.
> 
> Alex

I think we should first ack and commit this patch as it is sure it is needed.

Regarding the SRR1 question, it can be another patch because it is more 
general than the POW bit.
In the commit c3d420e which was about MSR restoring in RFI, I have removed the 
clearing of bits in SRR1. But I am OK to redo it after check that some 
exceptions doesn't rely on the presence of these bits. I mean clearing bits in 
SRR1 can be architecture-specific and exception-specific. Each exception has its 
own scheme for SRR1 clearing.

-- 
Thomas

Re: [Qemu-devel] [PATCH] target-ppc: clear MSR_POW on interrupt

[Edgar E. Iglesias]

On Fri, Sep 10, 2010 at 06:58:10PM +0200, Thomas Monjalon wrote:
> Alexander Graf wrote:
> > Am 10.09.2010 um 18:08 schrieb "Edgar E. Iglesias" 
> <edgar.iglesias@gmail.com>:
> > > On Fri, Sep 10, 2010 at 05:50:27PM +0200, Alexander Graf wrote:
> > >> Thomas Monjalon wrote:
> > >>> Alexander Graf wrote:
> > >>>> Thomas Monjalon wrote:
> > >>>>> Alexander Graf wrote:
> > >>>>>> Thomas Monjalon wrote:
> > >>>>>>> From: till <608107@bugs.launchpad.net>
> > >>>>>>> 
> > >>>>>>> According to FreeScale's 'Programming Environments Manual for
> > >>>>>>> 32-bit Implementations of the PowerPC Architecture' [MPCFPE32B,
> > >>>>>>> Rev.3, 9/2005], section 6.5, table 6-7, an interrupt resets
> > >>>>>>> MSR_POW to zero but qemu-0.12.4 fails to do so.
> > >>>>>>> Resetting the bit is necessary in order to bring the processor out
> > >>>>>>> of power management since otherwise it goes to sleep right away in
> > >>>>>>> the exception handler, i.e., it is impossible to leave PM-mode.
> > >>>>>> 
> > >>>>>> This doesn't look right. POW shouldn't even get stored in SRR1.
> > >>>>>> Could you please redo the patch and make sure that mtmsr masks out
> > >>>>>> MSR_POW?
> > >>>>> 
> > >>>>> Could you point sections of the specification for these requirements
> > >>>>> ?
> > >>>>> 
> > >>>>> I think SRR1 can save any bits. Non significant bits can be overriden
> > >>>>> and are masked out when RFI occurs.
> > >>>> 
> > >>>> I'm not saying I'm 100% sure on this, but take a look at the e300
> > >>>> reference manual
> > >>>> (http://cache.freescale.com/files/32bit/doc/ref_manual/e300coreRM.pdf)
> > >>>> section 5.2.3. POW is bit 13 in this notion. I don't see it getting
> > >>>> saved to SRR1.
> > >>> 
> > >>> The current implementation (commit c3d420e) save all the bits and
> > >>> restore only the needed ones (excluding POW). So POW is cleared after
> > >>> an interrupt.
> > >>> 
> > >>> But the subject of this patch wasn't on saved bits. It is to clear POW
> > >>> in the interrupt context. For an unknown reason, it's not done and
> > >>> it's clearly a bug to fix.
> > >> 
> > >> I completely agree. In fact, the mere fact that a bit can slip through
> > >> this loop indicates that something goes wrong.
> > >> 
> > >> As far as SRR1 goes, PowerISA 2.06 draws an even more complicated
> > >> picture: Page 816 says that SRR1 bits 42:44 indicate the power save exit
> > >> reason while 46:47 indicate how much state was transferred. Bit 45 would
> > >> be MSR_POW which is defined as "set to 0".
> > >> 
> > >> Because that means that we'll have to set MSR_POW in to 0 in SRR1 and
> > >> the interrupt switching function, we can just set it to 0 on mtmsr. That
> > >> was my point :).
> > > 
> > > Hi,
> > > 
> > > I'm not very familiar with PPC but the way I interpret it, we should
> > > clear the POW bit in both MSR and SRR1 when the interrupt waking the CPU
> > > is taken. While the CPU is sleeping, the POW bit should remain set in
> > > MSR though.
> > > 
> > > As Alex comments, the submited patch fails to make sure the SRR1 bit
> > > 13 is cleared when taking the interrupt, but I don't think clearing
> > > MSR[POW] in mtmsr is the right thing. In practice it probably doesn't
> > > matter much, possibly a bit annoying if you inspect the sleeping state
> > > from a debugger or similar.
> > > 
> > > I think mtmsr should set MSR[POW] and powerpc_excp() should clear
> > > MSR[POW] prior to copying MSR into SRR1.
> > > 
> > > Not sure, but thats the way I interpret it...
> > 
> > Agreed.
> > 
> > Alex
> 
> I think we should first ack and commit this patch as it is sure it is needed.
> 
> Regarding the SRR1 question, it can be another patch because it is more 
> general than the POW bit.
>
> In the commit c3d420e which was about MSR restoring in RFI, I have removed the 
> clearing of bits in SRR1. But I am OK to redo it after check that some 
> exceptions doesn't rely on the presence of these bits. I mean clearing bits in 
> SRR1 can be architecture-specific and exception-specific. Each exception has its 
> own scheme for SRR1 clearing.

But the MSR[POW] should be cleared prior to beeing copied to
SRR1. I dont see the point in submitting a followup patch
that moves the clearing a couple of lines up the c-file.

What about the following?

commit 7022e89d74a4299dbb431c89a684a428119242ab
Author: Edgar E. Iglesias <edgar.iglesias@gmail.com>
Date:   Fri Sep 10 21:36:09 2010 +0200

    powerpc: Clear MSR[POW] when taking exceptions
    
    When taking exceptions, clear the POW or WE bit to inditcate
    that the CPU is awake. Do it prior to saving the MSR into SRR1.
    
    Signed-off-by: Edgar E. Iglesias <edgar.iglesias@gmail.com>

diff --git a/target-ppc/helper.c b/target-ppc/helper.c
index d342b09..c25c610 100644
--- a/target-ppc/helper.c
+++ b/target-ppc/helper.c
@@ -2075,6 +2075,8 @@ static inline void powerpc_excp(CPUState *env, int excp_model, int excp)
     qemu_log_mask(CPU_LOG_INT, "Raise exception at " TARGET_FMT_lx
                   " => %08x (%02x)\n", env->nip, excp, env->error_code);
     msr = env->msr;
+    /* Taking an exception wakes up the core, clear the POW/WE bit.  */
+    msr &= ~((target_ulong)1 << MSR_POW);
     new_msr = msr;
     srr0 = SPR_SRR0;
     srr1 = SPR_SRR1;

Re: [Qemu-devel] [PATCH] target-ppc: clear MSR_POW on interrupt

[Alexander Graf]

On 10.09.2010, at 18:58, Thomas Monjalon wrote:

> Alexander Graf wrote:
>> Am 10.09.2010 um 18:08 schrieb "Edgar E. Iglesias" 
> <edgar.iglesias@gmail.com>:
>>> On Fri, Sep 10, 2010 at 05:50:27PM +0200, Alexander Graf wrote:
>>>> Thomas Monjalon wrote:
>>>>> Alexander Graf wrote:
>>>>>> Thomas Monjalon wrote:
>>>>>>> Alexander Graf wrote:
>>>>>>>> Thomas Monjalon wrote:
>>>>>>>>> From: till <608107@bugs.launchpad.net>
>>>>>>>>> 
>>>>>>>>> According to FreeScale's 'Programming Environments Manual for
>>>>>>>>> 32-bit Implementations of the PowerPC Architecture' [MPCFPE32B,
>>>>>>>>> Rev.3, 9/2005], section 6.5, table 6-7, an interrupt resets
>>>>>>>>> MSR_POW to zero but qemu-0.12.4 fails to do so.
>>>>>>>>> Resetting the bit is necessary in order to bring the processor out
>>>>>>>>> of power management since otherwise it goes to sleep right away in
>>>>>>>>> the exception handler, i.e., it is impossible to leave PM-mode.
>>>>>>>> 
>>>>>>>> This doesn't look right. POW shouldn't even get stored in SRR1.
>>>>>>>> Could you please redo the patch and make sure that mtmsr masks out
>>>>>>>> MSR_POW?
>>>>>>> 
>>>>>>> Could you point sections of the specification for these requirements
>>>>>>> ?
>>>>>>> 
>>>>>>> I think SRR1 can save any bits. Non significant bits can be overriden
>>>>>>> and are masked out when RFI occurs.
>>>>>> 
>>>>>> I'm not saying I'm 100% sure on this, but take a look at the e300
>>>>>> reference manual
>>>>>> (http://cache.freescale.com/files/32bit/doc/ref_manual/e300coreRM.pdf)
>>>>>> section 5.2.3. POW is bit 13 in this notion. I don't see it getting
>>>>>> saved to SRR1.
>>>>> 
>>>>> The current implementation (commit c3d420e) save all the bits and
>>>>> restore only the needed ones (excluding POW). So POW is cleared after
>>>>> an interrupt.
>>>>> 
>>>>> But the subject of this patch wasn't on saved bits. It is to clear POW
>>>>> in the interrupt context. For an unknown reason, it's not done and
>>>>> it's clearly a bug to fix.
>>>> 
>>>> I completely agree. In fact, the mere fact that a bit can slip through
>>>> this loop indicates that something goes wrong.
>>>> 
>>>> As far as SRR1 goes, PowerISA 2.06 draws an even more complicated
>>>> picture: Page 816 says that SRR1 bits 42:44 indicate the power save exit
>>>> reason while 46:47 indicate how much state was transferred. Bit 45 would
>>>> be MSR_POW which is defined as "set to 0".
>>>> 
>>>> Because that means that we'll have to set MSR_POW in to 0 in SRR1 and
>>>> the interrupt switching function, we can just set it to 0 on mtmsr. That
>>>> was my point :).
>>> 
>>> Hi,
>>> 
>>> I'm not very familiar with PPC but the way I interpret it, we should
>>> clear the POW bit in both MSR and SRR1 when the interrupt waking the CPU
>>> is taken. While the CPU is sleeping, the POW bit should remain set in
>>> MSR though.
>>> 
>>> As Alex comments, the submited patch fails to make sure the SRR1 bit
>>> 13 is cleared when taking the interrupt, but I don't think clearing
>>> MSR[POW] in mtmsr is the right thing. In practice it probably doesn't
>>> matter much, possibly a bit annoying if you inspect the sleeping state
>>> from a debugger or similar.
>>> 
>>> I think mtmsr should set MSR[POW] and powerpc_excp() should clear
>>> MSR[POW] prior to copying MSR into SRR1.
>>> 
>>> Not sure, but thats the way I interpret it...
>> 
>> Agreed.
>> 
>> Alex
> 
> I think we should first ack and commit this patch as it is sure it is needed.
> 
> Regarding the SRR1 question, it can be another patch because it is more 
> general than the POW bit.
> In the commit c3d420e which was about MSR restoring in RFI, I have removed the 
> clearing of bits in SRR1. But I am OK to redo it after check that some 
> exceptions doesn't rely on the presence of these bits. I mean clearing bits in 
> SRR1 can be architecture-specific and exception-specific. Each exception has its 
> own scheme for SRR1 clearing.

I'm really torn on this one. While you're right, I'd really like to see both issues fixed. To be honest, I don't think the whole function as is makes too much sense. Why would the MSR of an exception handler be based off the MSR we had before?


Alex

[Qemu-devel] [Bug 608107] Re: ppc fails to clear MSR_POW when incurring exception

[till]

I'm afraid I don't understand. My the problem and fix doesn't address mtmsr at all.
It just makes sure MSR_POW is cleared in MSR when an exception occurs.

Do you mean MSR_POW should masked from MSR before saving it to SRR1?
That's already taken care of (target-ppc/helper.c:2074 [qemu-0.12.4]).

-- 
ppc fails to clear MSR_POW when incurring exception
https://bugs.launchpad.net/bugs/608107
You received this bug notification because you are a member of qemu-
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Status in QEMU: Confirmed

Bug description:
QEMU VERSION: 0.12.4

According to FreeScale's 'Programming Environments Manual for 32-bit Implementations of the PowerPC Architecture' [MPCFPE32B, Rev.3, 9/2005], section 6.5, table 6-7, an interrupt resets MSR_POW to zero but qemu-0.12.4 fails to do so.
Resetting the bit is necessary in order to bring the processor out of power-management since otherwise it goes to sleep right away in the exception handler, i.e., it is impossible to leave PM-mode.

[Qemu-devel] [Bug 608107] Re: ppc fails to clear MSR_POW when incurring exception

[Samuel Bronson]

** Tags added: ppc

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https://bugs.launchpad.net/bugs/608107

Title:
  ppc fails to clear MSR_POW when incurring exception

Status in QEMU:
  Confirmed

Bug description:
  QEMU VERSION: 0.12.4

  According to FreeScale's 'Programming Environments Manual for 32-bit Implementations of the PowerPC Architecture' [MPCFPE32B, Rev.3, 9/2005], section 6.5, table 6-7, an interrupt resets MSR_POW to zero but qemu-0.12.4 fails to do so.
  Resetting the bit is necessary in order to bring the processor out of power-management since otherwise it goes to sleep right away in the exception handler, i.e., it is impossible to leave PM-mode.

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[Qemu-devel] [Bug 608107] Re: ppc fails to clear MSR_POW when incurring exception

[Thomas Huth]

As far as I can see, this problem has been fixed by this commit here:
http://git.qemu.org/?p=qemu.git;a=commitdiff;h=41557447d30eeb944e4
... so I'm setting the status to "Fix released" now.

** Changed in: qemu
       Status: Confirmed => Fix Released

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https://bugs.launchpad.net/bugs/608107

Title:
  ppc fails to clear MSR_POW when incurring exception

Status in QEMU:
  Fix Released

Bug description:
  QEMU VERSION: 0.12.4

  According to FreeScale's 'Programming Environments Manual for 32-bit Implementations of the PowerPC Architecture' [MPCFPE32B, Rev.3, 9/2005], section 6.5, table 6-7, an interrupt resets MSR_POW to zero but qemu-0.12.4 fails to do so.
  Resetting the bit is necessary in order to bring the processor out of power-management since otherwise it goes to sleep right away in the exception handler, i.e., it is impossible to leave PM-mode.

To manage notifications about this bug go to:
https://bugs.launchpad.net/qemu/+bug/608107/+subscriptions