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From: Richard Henderson <richard.henderson@linaro.org>
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Date: Sat, 19 Jan 2019 08:58:36 +1100
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Subject: Re: [Qemu-devel] [PATCH v10 14/14] target/arm: Send interrupts on
 PMU counter overflow
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To: Aaron Lindsay <aaron@os.amperecomputing.com>
Cc: "qemu-arm@nongnu.org" <qemu-arm@nongnu.org>, Peter Maydell <peter.maydell@linaro.org>, Alistair Francis <alistair.francis@xilinx.com>, Wei Huang <wei@redhat.com>, Peter Crosthwaite <crosthwaite.peter@gmail.com>, "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>, Michael Spradling <mspradli@codeaurora.org>, Digant Desai <digantd@codeaurora.org>, Aaron Lindsay <alindsay@codeaurora.org>

On 1/19/19 8:40 AM, Aaron Lindsay wrote:
> In practice, I think only the 32nd bit would ever need to be cleared,
> but I agree it is more correct to clear them all.
> 
>> Given that it is architecturally defined to 32-bits, I think you could really
>> just drop the define and use
>>
>>     uint32_t new_pmevcntr = ...;
>>     if (env->cp15.c14_pmevcntr[counter] & ~new_pmevcntr & INT32_MIN)
>>
>> with equal clarity.
> 
> I don't know whether it is important for the resolution of this patch,
> but what did you mean by the following?:
> 
>> The type of new_pmevcntr means you don't have to clear any
>> high bits either.

If you use uint32_t, then no *explicit* clearing of the high bits is necessary,
and is implied by the assignment back to env->cp15.c14_pmevcntr[counter].


r~