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

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Date:	Fri, 1 Mar 2013 08:38:34 -0600
From:	Nishanth Menon <nm@...com>
To:	Ивайло Димитров <freemangordon@....bg>
Cc:	pali.rohar@...il.com, tony@...mide.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

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.

Regards,
Nishanth Menon
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