Re: runtime check for omap-aes bus access permission (was: Re: 3.13-rc3 (commit 7ce93f3) breaks Nokia N900 DT boot)

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



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...

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.

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.

Or perhaps you could probe the device using a DMA access and combine
that with the interconnect error reporting irq... ;-)
--
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




[Index of Archives]     [Linux Arm (vger)]     [ARM Kernel]     [ARM MSM]     [Linux Tegra]     [Linux WPAN Networking]     [Linux Wireless Networking]     [Maemo Users]     [Linux USB Devel]     [Video for Linux]     [Linux Audio Users]     [Yosemite Trails]     [Linux Kernel]     [Linux SCSI]

  Powered by Linux