linux-kernel - RE: [PATCH 3/3] ARM: imx: add SMP support for i.MX7D

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Date:   Fri, 26 Aug 2016 10:28:15 +0000
From:   Yongcai Huang <anson.huang@....com>
To:     Arnd Bergmann <arnd@...db.de>
CC:     "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>,
        Fabio Estevam <fabio.estevam@....com>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "linux@...linux.org.uk" <linux@...linux.org.uk>
Subject: RE: [PATCH 3/3] ARM: imx: add SMP support for i.MX7D



Best Regards!
Anson Huang



> -----Original Message-----
> From: Arnd Bergmann [mailto:arnd@...db.de]
> Sent: 2016-08-26 4:59 PM
> To: Yongcai Huang <anson.huang@....com>
> Cc: linux-arm-kernel@...ts.infradead.org; devicetree@...r.kernel.org; linux-
> kernel@...r.kernel.org; shawnguo@...nel.org; kernel@...gutronix.de;
> Fabio Estevam <fabio.estevam@....com>; robh+dt@...nel.org;
> mark.rutland@....com; linux@...linux.org.uk
> Subject: Re: [PATCH 3/3] ARM: imx: add SMP support for i.MX7D
> 
> On Friday, August 26, 2016 7:12:51 PM CEST Anson Huang wrote:
> > i.MX7D has 2 cortex-a7 ARM core, add support for booting up SMP kernel
> > with 2 CPUs.
> >
> > The existing i.MX SMP code is designed for i.MX6 series SoCs which
> > have cortex-a9 ARM core, but i.MX7D has 2 cortex-a7 ARM core, so we
> > need to add runtime check for those differences between cortex-a9 and
> > cortex-a7.
> >
> > Signed-off-by: Anson Huang <Anson.Huang@....com>
> >
> 
> Can't you just point i.MX7D to start from secondary_startup rather than
> v7_secondary_startup?
> 
>  ENTRY(v7_secondary_startup)
> +       .word   0xc070                  @ 0xc07 is cortex-a7 id
> +       .word   0xfff0                  @ mask for core type
> +
> 
> This looks like you are trying to execute instructions that are actually data. Does
> this work?
> 
> On a side note, could you rename v7_secondary_startup to
> imx6_secondary_startup? The name sounds overly generic on a multiplatform
> kernel.
> 
> 	Arnd


Thanks for review, yes, I made a mistake here, the data should put in another place,
but it accidently can work and boot up secondary CPU (see below the objdump),
 and also, I can just use  secondary_startup for i.MX7D. So I will
leave this file untouched, will verify the function next Mon and send out a V2 patch.

10 00000004 <v7_secondary_startup>:
 11    4:   0000c070        andeq   ip, r0, r0, ror r0
 12    8:   0000fff0        strdeq  pc, [r0], -r0

Anson.