Re: [PATCH] MIPS: CPS: Fix r1 .set mt assembler warning

[James Hogan <jhogan@kernel.org>]

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Hi Greg,

On Fri, Feb 02, 2018 at 01:34:20PM +1000, Greg Ungerer wrote:
> Hi James,
> 
> James Hogan wrote:
> > From 17278a91e04f858155d54bee5528ba4fbcec6f87 Mon Sep 17 00:00:00 2001
> > From: James Hogan <jhogan@kernel.org>
> > Date: Tue, 14 Nov 2017 12:01:20 +0000
> > Subject: [PATCH] MIPS: CPS: Fix r1 .set mt assembler warning
> > 
> > MIPS CPS has a build warning on kernels configured for MIPS32R1 or
> > MIPS64R1, due to the use of .set mt without a prior .set mips{32,64}r2:
> > 
> > arch/mips/kernel/cps-vec.S Assembler messages:
> > arch/mips/kernel/cps-vec.S:238: Warning: the `mt' extension requires MIPS32 revision 2 or greater
> > 
> > Add .set MIPS_ISA_LEVEL_RAW before .set mt to silence the warning.
> 
> This change breaks booting for me on a MediaTek MT7621 platform:
> 
>   ...
>   Calibrating delay loop... 586.13 BogoMIPS (lpj=2930688)^M
>   pid_max: default: 32768 minimum: 301^M
>   Mount-cache hash table entries: 1024 (order: 0, 4096 bytes)^M
>   Mountpoint-cache hash table entries: 1024 (order: 0, 4096 bytes)^M
>   Hierarchical SRCU implementation.^M
>   smp: Bringing up secondary CPUs ...^M
>   Reserved instruction in kernel code[#1]:^M
>   CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.15.0-ac0 #3^M
>   $ 0   : 00000000 00000001 00000000 00000000^M
>   $ 4   : 8501dd80 00000001 00000004 00000000^M
>   $ 8   : 00000004 00000002 00000001 ffffffff^M
>   $12   : 00000000 00000400 00000003 8501de00^M
>   $16   : 807d5ca0 8501dd80 00000000 00000001^M
>   $20   : 80842814 00000000 00000001 000000e0^M
>   $24   : fffffffc 00000001                  ^M
>   $28   : 85026000 85027de0 00000020 80013538^M
>   Hi    : 00000006^M
>   Lo    : 8e778000^M
>   epc   : 80656620 mips_cps_boot_vpes+0x4c/0x160^M
>   ra    : 80013538 cps_boot_secondary+0x280/0x440^M
>   Status: 11000403        KERNEL EXL IE ^M
>   Cause : 50800028 (ExcCode 0a)^M
>   PrId  : 0001992f (MIPS 1004Kc)^M
> 
> If I revert the patch then I can boot up again, all works as expected.
> 
> I am not exactly using a pure mainline 4.15 source base though.
> (I have a bunch of additional changes to make this platform actually work).
> 
> But this patch certainly does trap as above when present. I am using
> a gcc-5.4.0/binutils-2.25.1 toolchain.
> 
> Any thoughts?

Hmm, sorry about that.

If there is some more of the log which shows code around the EPC
(usually a few lines below where you stopped), that would be helpful to
see exactly whats happening. Perhaps it has used a 64-bit instruction.

When I build 32r2el_defconfig, that EPC (relative to mips_cps_boot_vpes)
is a move instruction, which is implemented with OR (which should be
safe on MIPS32 and MIPS64), both with binutils 2.28ish and 2.24ish (MTI
/ IMG toolchains, so they may have additional patches).

I'll try limiting the .set mt to code that needs it.

Thanks
James

> 
> Regards
> Greg
> 
> 
> > Fixes: 245a7868d2f2 ("MIPS: smp-cps: rework core/VPE initialisation")
> > Signed-off-by: James Hogan <jhogan@kernel.org>
> > Cc: Paul Burton <paul.burton@mips.com>
> > Cc: James Hogan <james.hogan@mips.com>
> > Cc: James Hogan <jhogan@kernel.org>
> > Cc: Paul Burton <paul.burton@mips.com>
> > Cc: linux-mips@linux-mips.org
> > Patchwork: https://patchwork.linux-mips.org/patch/17699/
> > Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
> > ---
> >  arch/mips/kernel/cps-vec.S | 2 ++
> >  1 file changed, 2 insertions(+)
> > 
> > diff --git a/arch/mips/kernel/cps-vec.S b/arch/mips/kernel/cps-vec.S
> > index c7ed260..e68e6e0 100644
> > --- a/arch/mips/kernel/cps-vec.S
> > +++ b/arch/mips/kernel/cps-vec.S
> > @@ -235,6 +235,7 @@ LEAF(mips_cps_core_init)
> >         has_mt  t0, 3f
> > 
> >         .set    push
> > +       .set    MIPS_ISA_LEVEL_RAW
> >         .set    mt
> > 
> >         /* Only allow 1 TC per VPE to execute... */
> > @@ -388,6 +389,7 @@ LEAF(mips_cps_boot_vpes)
> >  #elif defined(CONFIG_MIPS_MT)
> > 
> >         .set    push
> > +       .set    MIPS_ISA_LEVEL_RAW
> >         .set    mt
> > 
> >         /* If the core doesn't support MT then return */
> > -- 
> > 1.9.1
> 

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