On 11/14/2012 02:32 PM, Tony Lindgren wrote: > * Russell King - ARM Linux <linux@xxxxxxxxxxxxxxxx> [121114 12:24]: >> On Wed, Nov 14, 2012 at 01:06:53PM -0600, Jon Hunter wrote: >>> >>> On 11/14/2012 12:53 PM, Tony Lindgren wrote: >>>> Looks like enabling CONFIG_ARM_ERRATA_751472 causes omap4 blaze >>>> to not boot when enabled. The ARM core on it is an earlier r1p2: >>>> >>>> CPU: ARMv7 Processor [411fc092] revision 2 (ARMv7), cr=10c53c7d >>>> >>>> Unfortunately I don't have the details of errata 751472, but I'm >>>> guessing we need to disable it for r1p*. >>> >>> I checked the CA9MP errata document and this erratum impacts all >>> r0/r1/r2 CPUs. I am wondering if the problem is because the workaround >>> requires you to set a bit in the Diagnostic Control register and the >>> read-modify-write sequence provided in the workaround is for secure >>> mode. Not sure if there is a non-secure workaround available :-( >> >> Most likely, and there's not a lot that the kernel can sanely do about >> that. We have ended up deciding (through being forced to because of >> how the security stuff works) that the stages prior to the kernel will >> implement the work-around enables because those stages are already >> platform specific, and the kernel will implement a "test for the >> work-around already enabled." >> >> The net result is, if you enable an Errata in the kernel which your >> earlier boot stages has not already configured, the kernel will hang. >> Not much we can do about the hanging aspect, because the kernel takes >> an exception which we can't trap at those early stages in the boot >> process. >> >> I'm not particularly happy about that design, but that's what we've >> ended up with through the 'design' of the security stuff forced onto >> us. > > 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? Multi-platform kernels present a new problem in that we basically need to enable all errata work-arounds. I've been meaning to look thru the errata work-arounds to figure out which ones can be selected for multi-platform kernels without side effects on unaffected parts (i.e. set a chicken bit based on core revision). For any in runtime paths, we may need to do runtime patching if they have performance impact. Rob -- 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
