* Matthijs van Duin <matthijsvanduin@xxxxxxxxx> [150528 18:37]: > On 29 May 2015 at 02:58, Matthijs van Duin <matthijsvanduin@xxxxxxxxx> wrote: > > It is only guaranteed to happen immediately (before the next > > instruction is executed) if the error occurs before the posting-point > > of the write. However, in that case the error is reported in-band to > > the cpu, resulting in a (synchronous) bus error which takes precedence > > over the out-of-band error irq (if any is signalled). > > OK, all this was actually assuming linux uses device-type mappings for > device mappings, which was also the impression I got from > build_mem_type_table() in arch/arm/mm/mmu.c (although it's a bit of a > maze). A quick test however seems to imply otherwise: > > ~# ./bogus-dev-write > Bus error > > So... linux actually uses strongly-ordered mappings? I really didn't > expect that, given the performance implications (especially on a > strictly in-order cpu like the Cortex-A8 which will really just sit > there picking its nose until the write completes) and I think I recall > having seen an OCP barrier being used somewhere in driver code... I believe some TI kernels use strongly-ordered mappings, mainline kernel does not. Which kernel version are you using? > Well, in that case everything I said is technically still true, except > the posting point is the peripheral itself. That also means the > interconnect error reporting mechanism is not really useful for > probing since you'll get a bus error before any error irq is > delivered. Hmm if that's the case then yes we can't use the error irq. However, what I've seen so far is that we only get the bus error if the l3_* drivers are configured. I guess some more testing is needed. > So I'd say you're back at having to trap that bus error using the > exception handling mechanism, which I still suspect shouldn't be hard > to do. And in that case it makes sense to do that in the bootloader to avoid adding any custom early boot code to Linux kernel. > Or perhaps you could probe the device using a DMA access and combine > that with the interconnect error reporting irq... ;-) Heh too many dependencies :) Tony -- 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
