On 11/15/2012 05:01 AM, Catalin Marinas wrote: > On Thu, Nov 15, 2012 at 12:54:48AM +0000, Rob Herring wrote: >> On 11/14/2012 04:21 PM, Tony Lindgren wrote: >>> * Rob Herring <robherring2@xxxxxxxxx> [121114 13:59]: >>>> On 11/14/2012 02:32 PM, Tony Lindgren wrote: >>>>> >>>>> Checking for the bit already set should work in this case, I'll post >>>>> a patch for that shortly. >>>> >>>> Can you actually read the state of the diagnostic register in non-secure >>>> mode? If you can on the A9, is the same true on A8 or others? >>> >>> Looks like it can be read on at least TI omap 4430 which is A9. >>> But it reads as zero, so the below patch is what I came up with. >>> >>> No idea if assuming that zero value for the diagnostic register >>> is safe.. What's the default value of the diagnostic register supposed >>> to be? >> >> RTFM. Oh, wait it's a super secret, undocumented register. We shouldn't >> even be talking about it. >> >> It could vary by rev, but I see 0 for the reset value, so this would not >> work if the bootloader did not do any setup of the diagnostic register. >> >> One way to determine secure mode on the A9 would be seeing if you can >> change the auxcr register. Something like this (untested): >> >> mrc p15, 0, r0, c1, c0, 1; Read ACTLR >> eor r1, r0, #0x100 ; Modify alloc in 1 way >> mcr p15, 0, r1, c1, c0, 1 >> mrc p15, 0, r2, c1, c0, 1; Read ACTLR >> mcr p15, 0, r0, c1, c0, 1 ; Restore original value >> cmp r1, r2 >> bne skip_errata > > This would fail on platforms where Linux runs in non-secure mode. What > we do for some errata workarounds is to test whether the bit was already > set and avoid writing the register. But this assumes that, for a given > workaround in the kernel, there is a corresponding workaround in the > code running before the kernel (boot-loader, firmware) which sets that > bit. > > Since the kernel will run more often in non-secure mode (on Cortex-A15 > you need this for the virtualisation extensions) I strongly suggest that > the workaround (usually undocumented bit setting) is done before the > kernel is started and we simply remove it from Linux (or add a clear > comment that it only works if running in secure mode; if unsure say > 'N'). > > I don't think it's worth the hassle detecting whether the kernel runs in > secure or non-secure mode, just assume the latter and get SoC vendors to > update the boot loaders or firmware (if possible) with any errata > workarounds. There's other places we need to know secure vs. non-secure mode like whether we can do smc calls or not. So we should make all these work-arounds depend on !MULTI_PLATFORM then. Does that work for Versatile Express CA9? It needs ARM_ERRATA_751472. Rob > > Having a common SMC API for errata workarounds is not feasible since not > all registers are public, most are implementation specific and it could > have secure implications with exposing them. > -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
