Messages in this thread | | | Date | Tue, 01 Feb 2005 13:01:33 -0600 | From | Brian King <> | Subject | Re: [PATCH 1/1] pci: Block config access during BIST (resend) |
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Matthew Wilcox wrote: > On Tue, Feb 01, 2005 at 11:35:05AM -0600, Brian King wrote: > >>>If we've done a write to config space while the adapter was blocked, >>>shouldn't we replay those accesses at this point? >> >>I did not think that was necessary. > > > We have to do *something*. We can't just throw away writes. > > I see a few options: > > - Log all pending writes to config space and replay the log when the > device is unblocked.
This would need to be dynamic in size, as a device could be blocked for a long time. In the scenario that this is used for power management and the device could be blocked for a long time, its unclear that we would still want all the writes accumulated to be written out when the device becomes unblocked.
> - Fail writes to config space while the device is blocked.
This would be nice and simple. I know Alan had some issue with returning failures on reads when blocked.
Alan - do you have the same issue on writes?
> - Write to the saved config space and then blat the saved config space > back to the device upon unblocking.
Would also be pretty simple to do and seems a little safer than potentially assaulting the recently unblocked device with who knows what values. The only problem I see with this is that we could end up returning strange values on cached reads if the writes update the cache. If userspace wrote to a read only register, we would end up returning that value on the read, which may not be the right thing to do.
> Any other ideas?
We could go back to Alan's idea of putting userspace reads/writes to sleep when the device is blocked, although this has additional complications as well...
> BTW, you know things like XFree86 go completely around the kernel's PCI > accessors and poke at config space directly?
The purpose of this API is to provide a way for the kernel to stop userspace from accessing PCI devices when the results of doing so would be catastrophic, such as a PCI bus error. The only users of this API so far are device drivers running BIST on an adapter (which shouldn't happen on a video card AFAIK) and for PPC power management (Ben - will this be an issue for you?)
-- Brian King eServer Storage I/O IBM Linux Technology Center - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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