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Re: [Qemu-arm] [PATCH v4 2/3] utils: Add helper to read arm MIDR_EL1 reg


From: Vijay Kilari
Subject: Re: [Qemu-arm] [PATCH v4 2/3] utils: Add helper to read arm MIDR_EL1 register
Date: Fri, 4 Nov 2016 20:24:09 +0530

Hi Peter

On Fri, Oct 28, 2016 at 3:39 PM, Vijay Kilari <address@hidden> wrote:
> On Fri, Oct 28, 2016 at 2:33 PM, Peter Maydell <address@hidden> wrote:
>> On 28 October 2016 at 08:00, Vijay Kilari <address@hidden> wrote:
>>> On Thu, Oct 27, 2016 at 9:33 PM, Peter Maydell <address@hidden> wrote:
>>>> On 25 October 2016 at 13:12,  <address@hidden> wrote:
>>>>> From: Vijaya Kumar K <address@hidden>
>>>>>
>>>>> Add helper API to read MIDR_EL1 registers to fetch
>>>>> cpu identification information. This helps in
>>>>> adding errata's and architecture specific features.
>>>>>
>>>>> This is implemented only for arm architecture.
>>>>>
>>>>> Signed-off-by: Vijaya Kumar K <address@hidden>
>>
>>>>> diff --git a/util/Makefile.objs b/util/Makefile.objs
>>>>> index 36c7dcc..d14a455 100644
>>>>> --- a/util/Makefile.objs
>>>>> +++ b/util/Makefile.objs
>>>>> @@ -37,3 +37,4 @@ util-obj-y += log.o
>>>>>  util-obj-y += qdist.o
>>>>>  util-obj-y += qht.o
>>>>>  util-obj-y += range.o
>>>>> +util-obj-y += aarch64-cpuid.o
>>
>>>>
>>>>> +#include "qemu/cutils.h"
>>>>> +#include "qemu/aarch64-cpuid.h"
>>>>> +
>>>>> +#if defined(__aarch64__)
>>>>> +static uint64_t qemu_read_aarch64_midr_el1(void)
>>>>> +{
>>>>> +#ifdef CONFIG_LINUX
>>>>
>>>> When will CONFIG_LINUX not be defined but __aarch64__ is?
>>>   The contents of this file is compiled only for aarch64
>>
>> Your makefile change compiles it for everything.
>>
>>> and hence
>>> all the contents are under this __aarch64__.
>>> Also the code is only for linux, have added CONFIG_LINUX.
>>
>> ...and you haven't answered the question: in what
>> circumstances could __aarch64__ be defined but
>> CONFIG_LINUX is not, ie why is there any point in
>> checking both defines?
>
> Ok. You mean __aarch64__ and __linux__ both are defined by gcc.
> we can rely on __aarch64__ define  here?.
>
> AFAIK, the caller of this function bufferiszero.c is compiled
> for everything, I case of bufferiszero.c is compiled for other than
> linux for aarch64, compilation might fail. In such case, the header file
> needs to have dummy/empty functions.

What do you suggest for this?.

Regards
Vijay



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