linux-kernel - Re: [PATCH] arm: omap: RX-51: ARM errata 430973 workaround

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Message-ID: <20130304185806.GS11806@atomide.com>
Date:	Mon, 4 Mar 2013 10:58:06 -0800
From:	Tony Lindgren <tony@...mide.com>
To:	Nishanth Menon <nm@...com>
Cc:	Ивайло Димитров 
	<freemangordon@....bg>, pali.rohar@...il.com,
	linux@....linux.org.uk, linux-kernel@...r.kernel.org,
	linux-omap@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] arm: omap: RX-51: ARM errata 430973 workaround

* Nishanth Menon <nm@...com> [130301 06:42]:
> On Fri, Mar 1, 2013 at 1:47 AM, Ивайло Димитров <freemangordon@....bg> wrote:
> >
> > They look similar, but they are not equivalent :). The first major difference is here (code taken from omap-smc.S)
> >
> >> ENTRY(omap_smc2)
> >>          stmfd   sp!, {r4-r12, lr}
> >>          mov     r3, r2
> >>          mov     r2, r1
> >>          mov     r1, #0x0        @ Process ID
> >>          mov     r6, #0xff
> >>          mov     r12, #0x00      @ Secure Service ID
> >
> > Always zero, while RX51 PPA expects a real value. I wonder if it is a bug, but anyway I don't see the id parameter (R0) used.
> >
> >>          mov     r7, #0
> >>          mcr     p15, 0, r7, c7, c5, 6
> >
> > According to ARM TRM, this is "Invalidate entire branch predictor array"(IIUC). NFC why it is needed here, but this will not work on RX-51 until IBE bit in ACR is set.
> >
> >>          dsb
> >>          dmb
> >>          smc     #0
> >
> > RX-51 needs smc #1 ;)
> >
> >>          ldmfd   sp!, {r4-r12, pc}
> >
> >
> > The next major difference is that RX-51 expects parameter count passed in R3[0] to be the count of the remaining parameters +1, but omap_secure_dispatcher (in omap-secure.c) is passing the exact count of the remaining parameters.
> >
> > I guess all of the above problems can be fixed/workarounded, but I wonder does it worth. Not to say that I don't have BB around to test if the code still works if I make changes to omap2-secure.c/omap-smc.S :)
> >
> >
> 
> Yep, that was my point - instead of introducing new functions,
> extending the existing functions to handle new requirements is better
> solution, IMHO.

I think there have been patches posted for ARM generic SMC
handling. Might be worth looking at those a bit and see if
this can be made generic. I think only the SMC call numbering
is different for various SoCs?

Regards,

Tony
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