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From:   Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>
To:     Vineet Gupta <Vineet.Gupta1@synopsys.com>,
        "linux-snps-arc@lists.infradead.org" 
        <linux-snps-arc@lists.infradead.org>
CC:     "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "Alexey Brodkin" <Alexey.Brodkin@synopsys.com>
Subject: Re: [PATCH 4/5] ARC: add support for DSP-enabled userspace
 applications
Thread-Topic: [PATCH 4/5] ARC: add support for DSP-enabled userspace
 applications
Thread-Index: AQHVvOALEgJG1jhHKUKrXAMj7igcXqfflg6AgFkkVq8=
Date:   Wed, 4 Mar 2020 11:51:17 +0000
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 <20191227180347.3579-5-Eugeniy.Paltsev@synopsys.com>,<a3890ccb-e948-6ad6-c2ea-5b77b9d3a289@synopsys.com>
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Hi Vineet,=0A=
=0A=
>From: Vineet Gupta <vgupta@synopsys.com>=0A=
>Sent: Tuesday, January 7, 2020 21:25=0A=
>To: Eugeniy Paltsev; linux-snps-arc@lists.infradead.org=0A=
>Cc: linux-kernel@vger.kernel.org; Alexey Brodkin=0A=
>Subject: Re: [PATCH 4/5] ARC: add support for DSP-enabled userspace applic=
ations=0A=
>> +/*=0A=
>> + * As we save new and restore old AUX register value in the same place =
we=0A=
>> + * can optimize a bit and use AEX instruction (swap contents of an auxi=
liary=0A=
>> + * register with a core register) instead of LR + SR pair.=0A=
>> + */=0A=
>> +#define AUX_SAVE_RESTORE(_saveto, _readfrom, _offt, _aux, _scratch)  \=
=0A=
>> +do {                                                                 \=
=0A=
>> +     __asm__ __volatile__(                                           \=
=0A=
>> +             "ld     %0, [%2, %4]                    \n"             \=
=0A=
>> +             "aex    %0, [%3]                        \n"             \=
=0A=
>> +             "st     %0, [%1, %4]                    \n"             \=
=0A=
>> +             :                                                       \=
=0A=
>> +               "=3D&r" (_scratch)      /* must be early clobber */     =
\=0A=
>> +             :                                                       \=
=0A=
>> +                "r" (_saveto),                                       \=
=0A=
>> +                "r" (_readfrom),                                     \=
=0A=
>> +                "I" (_aux),                                          \=
=0A=
>> +                "I" (_offt)                                          \=
=0A=
>> +             :                                                       \=
=0A=
>=0A=
>AEX with "I" constraint will likely be an 8 byte instructions always. Best=
 to give=0A=
>compiler wiggle room with "Ir"=0A=
=0A=
Could you please explain how "Ir" will work in this case?=0A=
Does this mean that compiler can pass the value either as constant ('I') or=
=0A=
via register ('r')?=0A=
=0A=
Note that in this case both _aux and _offt are compile-time constants -=0A=
_aux comes from define and _offt comes from offsetof().=0A=
=0A=
>> +               "memory"                                              \=
=0A=
>> +     );                                                              \=
=0A=
>> +} while (0)=0A=
>> +=