Re: [RFC PATCH] ARM: Add imprecise abort enable/disable macro

[Ben Dooks]

On 10/02/14 15:21, Dave Martin wrote:
> On Mon, Feb 10, 2014 at 02:54:22PM +0000, Ben Dooks wrote:
> > On 10/02/14 14:16, Dave Martin wrote:
> > > On Fri, Feb 07, 2014 at 05:19:15PM +0100, Fabrice GASNIER wrote:
> > > > This patch adds imprecise abort enable/disable macros.
> > > > It also enables imprecise aborts when starting kernel.
> > >
> > > Relying on imprecise aborts for hardware probing would be considered bad
> > > hardware and/or software design for ARM-specific stuff.
> > >
> > > PCI is more generic though, so we may have to put up with this to some
> > > extent.  Can you point me to the affected probing code?  I'm not very
> > > familiar with that stuff...
> >
> > The marvell pcie always had the option of delivering any bus
> > errors as imprecise aborts. However it was /annoying/ and therefore
>
> You don't say ;)
>
> > easier just to turn it off and rely on the hardware returning 0xffff
> > for any configuration area it couldn't get to.
>
> Does PCI have any way of finding out which parts of the configuration
> space are there before you are forced to go poking around in invalid
> address space?
>
> I'm guessing there may not be, otherwise this convsersation might not
> be happening ... but I don't know too much about PCI.

IIRC for configuration accesses you have to wait for the PCIe core
to get a response from the other end. The systems I've seen either
poll for completion or hold the transaction until the pcie core has
finished working.


--
Ben Dooks				http://www.codethink.co.uk/
Senior Engineer				Codethink - Providing Genius
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