linux-kernel - Re: [PATCH] ARC: guard dsp early init against non ARCv2

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Date:   Wed, 29 Apr 2020 18:50:21 +0000
From:   Vineet Gupta <Vineet.Gupta1@...opsys.com>
To:     Eugeniy Paltsev <Eugeniy.Paltsev@...opsys.com>
CC:     Alexey Brodkin <Alexey.Brodkin@...opsys.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-snps-arc@...ts.infradead.org" 
        <linux-snps-arc@...ts.infradead.org>
Subject: Re: [PATCH] ARC: guard dsp early init against non ARCv2

On 4/29/20 10:12 AM, Eugeniy Paltsev wrote:
> Hi Vineet, 
>
>> From: Vineet Gupta <vgupta@...opsys.com>
>> Sent: Tuesday, April 28, 2020 22:46
>> To: Eugeniy Paltsev; linux-snps-arc@...ts.infradead.org
>> Cc: Alexey Brodkin; linux-kernel@...r.kernel.org
>> Subject: Re: [PATCH] ARC: guard dsp early init against non ARCv2
>>
>> On 4/28/20 11:50 AM, Eugeniy Paltsev wrote:
>>> As of today we guard early DSP init code with
>>> ARC_AUX_DSP_BUILD (0x7A) BCR check to verify that we have
>>> CPU with DSP configured. However that's not enough as in
>>> ARCv1 CPU the same BCR (0x7A) is used for checking MUL/MAC
>>> instructions presence.
>>>
>>> So, let's guard DSP early init against non ARCv2.
>>>
>>> Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@...opsys.com>
>>> ---
>>>  arch/arc/include/asm/dsp-impl.h | 2 ++
>>>  1 file changed, 2 insertions(+)
>>>
>>> diff --git a/arch/arc/include/asm/dsp-impl.h b/arch/arc/include/asm/dsp-impl.h
>>> index e1aa212ca6eb..e64d945ae7df 100644
>>> --- a/arch/arc/include/asm/dsp-impl.h
>>> +++ b/arch/arc/include/asm/dsp-impl.h
>>> @@ -15,12 +15,14 @@
>>>
>>>  /* clobbers r5 register */
>>>  .macro DSP_EARLY_INIT
>>> +#if defined(CONFIG_ISA_ARCV2)
>> ifdef is the canonical way for a single macro to check.
>>
>> Also, this needs to be finer grained, i.e. CONFIG_ARC_DSP_KERNEL which is already
>> tied to ARCV2 only configs.
> We shouldn't limit the scope of this code part [dsp early init] to the cases
> were DSP support is enabled in kconfig - and that is the reason why this code
> initially was guarded with BCR check only.
>
> So, I change the check to
>
> #if defined(CONFIG_ARC_DSP_HANDLED) || defined(CONFIG_ARC_DSP_NONE)

You are right. It needs to be disabled if the hardware exists independent of Kconfig.

> which is actually the equivalent to
>
> #if defined(CONFIG_ISA_ARCV2)
>
> but I don't think it's worth thing to do.

Agree.

-Vineet