linux-kernel - Re: [PATCH] powerpc/8xx: use SPRN_EIE and SPRN

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Date:   Fri, 19 Aug 2016 08:59:45 +0200
From:   Christophe Leroy <christophe.leroy@....fr>
To:     Segher Boessenkool <segher@...nel.crashing.org>
Cc:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Scott Wood <oss@...error.net>, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] powerpc/8xx: use SPRN_EIE and SPRN_EID to enable/disable
 interrupts



Le 18/08/2016 à 19:54, Segher Boessenkool a écrit :
> On Thu, Aug 18, 2016 at 06:52:47PM +0200, Christophe Leroy wrote:
>> Le 18/08/2016 à 18:34, Segher Boessenkool a écrit :
>>> On Thu, Aug 18, 2016 at 05:56:02PM +0200, Christophe Leroy wrote:
>>>> The 8xx has two special registers called EID (External Interrupt
>>>> Disable) and EIE (External Interrupt Enable) for clearing/setting
>>>> EE in MSR. It avoids the three instructions set mfmsr/ori/mtmsr or
>>>> mfmsr/rlwinm/mtmsr.
>>>
>>> All 8xx?  What other models?  (5xx for example).
>>
>> At least 823, 860, 866 and 885 have it.
>
> I haven't been able to find a manual for all 8xx.  But there is AN2055,
> which suggests EIE etc. is for all 8xx indeed.
>
>> Looks like the 5xx have it too (at least the 565). Does Linux supports
>> that one at all ?
>
> All 5xx have it, there is a manual for *that* ("RCPU") :-)
>
>>>> +/* Special MSR manipulation registers */
>>>> +#define SPRN_EIE	80	/* External interrupt enable (EE=1, RI=1) */
>>>> +#define SPRN_EID	81	/* External interrupt disable (EE=0, RI=1) */
>>>> +#define SPRN_NRI	81	/* Non Recoverable interrupt (EE=0, RI=0) */
>
> Is it correct to set RI in all places you do now?

MSR_KERNEL contains the RI bit.
MSR_KERNEL less MSR_IR and MSR_DR is loaded into MSR in 
EXCEPTION_PROLOG_2() in head_8xx.S
Then reloaded with MSR_KERNEL in some places in entry_32.S

And MSR_RI is cleared in restore: in entry_32.S a few insns before the RFI.

So in all C functions, MSR_RI is set.

Christophe

>
>>> This is wrong (NRI is 82).  Don't write code you cannot test / don't submit
>>> code you haven't tested?  :-)
>>
>> Oops. You're right, copy/paste failure.
>> Was tested on an 885. Unfortunatly SPRN_NRI is not used (yet) :-(
>
> Well, that was my point!
>
>
> Segher
>