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Message-ID: <20130712102430.GA3249@localhost.localdomain>
Date: Fri, 12 Jul 2013 11:24:37 +0100
From: Dave Martin <Dave.Martin@....com>
To: Santosh Shilimkar <santosh.shilimkar@...com>
Cc: Ивайло Димитров
<freemangordon@....bg>, nm@...com, linux@....linux.org.uk,
aaro.koskinen@....fi, tony@...mide.com, pdeschrijver@...dia.com,
linux-kernel@...r.kernel.org, pavel@....cz, pali.rohar@...il.com,
linux-omap@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 1/2] ARM: OMAP: Add secure function omap_smc3() which
calling instruction smc #1
On Thu, Jul 11, 2013 at 03:54:34PM -0400, Santosh Shilimkar wrote:
> On Thursday 11 July 2013 03:43 PM, Ивайло Димитров wrote:
> >
> >
> >
> >
> >
> > >-------- Оригинално писмо --------
> > >От: Dave Martin
> > >Относно: Re: [PATCH v2 1/2] ARM: OMAP: Add secure function omap_smc3() which
> > calling instruction smc #1
> > >До: Pali Rohár
> > >Изпратено на: Сряда, 2013, Юли 10 20:45:26 EEST
> > >
> > >
> > >On Wed, Jul 10, 2013 at 02:59:04PM +0200, Pali Rohár wrote:
> > >> Other secure functions omap_smc1() and omap_smc2() calling instruction smc #0
> > >> but Nokia RX-51 board needs to call smc #1 for PPA access.
> > >>
> > >> Signed-off-by: Ivaylo Dimitrov
> > >> Signed-off-by: Pali Rohár
> > >> ---
> > >> arch/arm/mach-omap2/omap-secure.h | 1 +
> > >> arch/arm/mach-omap2/omap-smc.S | 22 +++++++++++++++++++++-
> > >> 2 files changed, 22 insertions(+), 1 deletion(-)
> > >>
> > >> diff --git a/arch/arm/mach-omap2/omap-secure.h b/arch/arm/mach-omap2/omap-secure.h
> > >> index 0e72917..c4586f4 100644
> > >> --- a/arch/arm/mach-omap2/omap-secure.h
> > >> +++ b/arch/arm/mach-omap2/omap-secure.h
> > >> @@ -51,6 +51,7 @@
> > >> extern u32 omap_secure_dispatcher(u32 idx, u32 flag, u32 nargs,
> > >> u32 arg1, u32 arg2, u32 arg3, u32 arg4);
> > >> extern u32 omap_smc2(u32 id, u32 falg, u32 pargs);
> > >> +extern u32 omap_smc3(u32 id, u32 process, u32 flag, u32 pargs);
> > >> extern phys_addr_t omap_secure_ram_mempool_base(void);
> > >> extern int omap_secure_ram_reserve_memblock(void);
> > >>
> > >> diff --git a/arch/arm/mach-omap2/omap-smc.S b/arch/arm/mach-omap2/omap-smc.S
> > >> index f6441c1..5c02b8d 100644
> > >> --- a/arch/arm/mach-omap2/omap-smc.S
> > >> +++ b/arch/arm/mach-omap2/omap-smc.S
> > >> @@ -1,9 +1,11 @@
> > >> /*
> > >> - * OMAP44xx secure APIs file.
> > >> + * OMAP34xx and OMAP44xx secure APIs file.
> > >> *
> > >> * Copyright (C) 2010 Texas Instruments, Inc.
> > >> * Written by Santosh Shilimkar
> > >> *
> > >> + * Copyright (C) 2012 Ivaylo Dimitrov
> > >> + * Copyright (C) 2013 Pali Rohár
> > >> *
> > >> * This program is free software,you can redistribute it and/or modify
> > >> * it under the terms of the GNU General Public License version 2 as
> > >> @@ -54,6 +56,24 @@ ENTRY(omap_smc2)
> > >> ldmfd sp!, {r4-r12, pc}
> > >> ENDPROC(omap_smc2)
> > >>
> > >> +/**
> > >> + * u32 omap_smc3(u32 service_id, u32 process_id, u32 flag, u32 pargs)
> > >> + * Low level common routine for secure HAL and PPA APIs via smc #1
> > >> + * r0 - @service_id: Secure Service ID
> > >> + * r1 - @process_id: Process ID
> > >> + * r2 - @flag: Flag to indicate the criticality of operation
> > >> + * r3 - @pargs: Physical address of parameter list
> > >> + */
> > >> +ENTRY(omap_smc3)
> > >> + stmfd sp!, {r4-r12, lr}
> > >
> > >You don't need to save/restore r12. The ABI allows it to be clobbered
> > >across function calls.
> > >
> > >> + mov r12, r0 @ Copy the secure service ID
> > >> + mov r6, #0xff @ Indicate new Task call
> > >> + dsb
> > >> + dmb
> > >
> > >dsb synchronises a superset of what dmb synchronises, so the dmb here is
> > >not useful.
> > >
> > >In any case, any code calling this must flush the region addressed by
> > >r3 beforehand anyway, which will include a dsb as part of its semantics
> > >-- this is how you call it from rx51_secure_dispatcher().
> > >
> > >So I think the dsb may not be needed here (?)
> > >
> > >Cheers
> > >---Dave
> > >
> > >
> >
> > Could be, but I wonder why almost all the kernel code(I am aware of) that uses SMC and is written by TI, is storing r12 and is using both DSB and DMB. See arch/arm/mach-omap2/sleep34xx.S or arch/arm/mach-omap2/omap-smc.S for examples. I'd rather play it safe and leave it that way, unless someone confirms the other code using SMC has extra DSB/DMB instructions too. I wouldn't risk passing invalid/stale data to the Secure Monitor to just save 8 bytes and barriers in a performance non-critical code which will be called only a couple of times during the boot-up process. r12 save/restore is a legacy from omap_smc2 in omap-smc.S, so I guess it can go away without much of a trouble.
> >
> Dave pointed out about the dsb and r12 to me in another thread. R12 can be easily removed
> but the DSB's were needed on OMAP for power sequencing. Without those, we have seen
> many issues. So you can leave the dsb's to be consistent with rest of the code.
Consistency is a perfectly good reason, especially in code like this
where a certain code sequence has been proven, but it's preferable to
include brief comments to explain nonetheless.
Difficulty in explaining precisely why something is needed should be a
warning flag that a comment is needed.
Cheers
---Dave
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