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Re: [Qemu-ppc] [Qemu-devel] [PATCH v2] PPC: Clean up DECR implementation

From: Tom Musta
Subject: Re: [Qemu-ppc] [Qemu-devel] [PATCH v2] PPC: Clean up DECR implementation
Date: Tue, 08 Apr 2014 16:17:05 -0500
User-agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:24.0) Gecko/20100101 Thunderbird/24.4.0

On 4/8/2014 2:58 PM, Alexander Graf wrote:
> On 04/08/2014 09:56 PM, Tom Musta wrote:
>> On 4/6/2014 3:55 PM, Alexander Graf wrote:
>> <snip>
>>> @@ -806,6 +838,10 @@ clk_setup_cb cpu_ppc_tb_init (CPUPPCState *env, 
>>> uint32_t freq)
>>>       tb_env = g_malloc0(sizeof(ppc_tb_t));
>>>       env->tb_env = tb_env;
>>>       tb_env->flags = PPC_DECR_UNDERFLOW_TRIGGERED;
>>> +    if (env->insns_flags & PPC_SEGMENT_64B) {
>>> +        /* All Book3S 64bit CPUs implement level based DEC logic */
>>> +        tb_env->flags |= PPC_DECR_UNDERFLOW_LEVEL;
>>> +    }
>>>       /* Create new timer */
>>>       tb_env->decr_timer = timer_new_ns(QEMU_CLOCK_VIRTUAL, 
>>> &cpu_ppc_decr_cb, cpu);
>>>       if (0) {
>> Equating Book3S with PPC_SEGMENT_64B is clever ... is it too clever?  
>> Especially since
>> the SLB Bridge is in the phased-out category and consequently we should 
>> expect future
>> Book3S implementations to not support this instruction category.
> Maybe it's too clever :). I'm very open to suggestions on how to figure this 
> out otherwise. Or maybe we should just rework the way timers get created and 
> make them be part of the core itself?

I don't think there are existing flags that successfully describe what you want.

It seems to me that an overall timer configuration mechanism would be nice to 
have.  This would include:
 - a list of timers supported by the processor (family)
 - read / write privileges for each timer.
 - additional attributes (e.g. edge triggered vs. level triggered DEC)

It would be great to have good default configurations for the current Book 
III-S and Book III-E.

Things like read/write perms have changed over time which makes this all that 
much more fun.

I need a little time to study Book III-E and review some old documents (e.g. 
601, 401/403, etc.).
I'll propose something a little more concrete.

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