linux-kernel - Re: [PATCH v2 1/2] ARM: OMAP: Add secure function omap

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Date:	Thu, 11 Jul 2013 22:43:59 +0300 (EEST)
From:	Ивайло Димитров 
	<freemangordon@....bg>
To:	Dave Martin <Dave.Martin@....com>
Cc:	pali.rohar@...il.com, linux-kernel@...r.kernel.org,
	tony@...mide.com, aaro.koskinen@....fi, nm@...com,
	linux@....linux.org.uk, pdeschrijver@...dia.com,
	santosh.shilimkar@...com, pavel@....cz, 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

 




 >-------- 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.
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