Re: pci error recovery procedure
- From: linas@xxxxxxxxxxxxxx (Linas Vepstas)
- Date: Fri, 1 Sep 2006 16:25:48 -0500
On Fri, Sep 01, 2006 at 11:33:49AM +0800, Zhang, Yanmin wrote:
On Fri, 2006-09-01 at 01:50, Linas Vepstas wrote:
On Thu, Aug 31, 2006 at 03:10:12PM +0800, Zhang, Yanmin wrote:Originally, I didn't think so, but after I try to add err_handlers to some
Linas,
I am reviewing the error handlers of e1000 driver and got some ideas. My
startpoint is to simplify the err handler implementations for drivers, or
driver developers are *not willing* to add it if it's too complicated.
I don't see that its to complicated ...
drivers, I feel it's too complicated.
Which drivers are you working on?
The new error_resume, or the old slot_reset could take care of it. The specific1) Callback mmio_enabled looks useless. Documentation/pci-error-recovery.txt
says the current powerpc implementation does not implement this callback.
I don't know if its useless or not. I have not needed it yet for the
symbios, ipr and e1000 drivers, but its possible that some more
sophisticated device may want it. I'm tempted to keep it a while
longer befoe discarding it.
The scenario is this: the device driver decides that, rather than asking
for a full electical reset of the card, instead, it wants to perform
its own recovery. It can do this as follows:
a) enable MMIO
b) issue reset command to adapter
c) enable DMA.
If we enabled both DMA and MMIO at the same time, there are mnay cases
where the card will immediately trap again -- for example, if its
DMA'ing to some crazy address. Thus, typically, one wants DMA disabled
until after the card reset. Withouth the mmio_enabled() reset, there
is no way of doing this.
device driver knows all the details about how to initiate the devices. The
error_resume could call the step a) b) c) sequencially while doing checking among
steps.
Again, consider the multi-function cards. On pSeries, I can only enable
DMA on a er-slot basis, not a per-function basis. So if one driver
enables DMA before some other driver has reset appropriately, everything
breaks.
If there is really a device having specific requirement to reinitiate it (very rarely),
it could use walkaround, such like schedule a WORKER. No need to provide a generic
mmio_enabled.
I don't understand. Enabling MMIO and enabling DMA both require specific
commands to be sent to the PCI-host bridge. These commands are not a
part of the PCI spec.
I don't think we need slot_reset to coordinate multi-function devices. The new2) Callback slot_reset could be merged with resume. The new resume could be:
int (*error_resume)(struct pci_dev *dev); I checked e1000 and e100 drivers and
think there is no actual reason to have both slot_reset and resume.
The idea here was to handle multi-function cards. On a multi-function card,
*all* devices need to indicate that they were able to reset. Once all devices
have been successfuly reset, then operation can be resumed. If the reset
of one function fails, then operation is not resumed for any f the
functions.
error_resume could take care of multi-function card.
How?
'reset' here means driver
need do I/O to detect if the device (function) still works well. If a function
of a multi-function device couldn't reset while other functions could reset,
other functions could just go on to reinitiate. In the end, the error recovery
procedure (handle_eeh_events in PowerPC implementation) could check all the
returning values of error_resume. If there is a failure value, then removes
all the functions' pci_dev of the device from the bus.
I can only enable or disable an entire PCI slot, and not individual PCI
functions. If there are some pins that are shorted, or parity errors or
whatever, I can only turn off the whole card.
Who will perform the electrical reset of the card? Function e1000_reset or the platform?During
our last discussion on LKML, you said PowerPC will block further I/O if the platform captures
a pci error, so the all I/O in e1000_down will be blocked. Later on, e1000_io_slot_reset
will reenable pci device and initiate NIC. I guess late initiate might fail because prior
e1000_down I/O don't reach NIC.
Why would it fail? The e1000_down serves primarily to get the Linux
kernel into a known state. It doesn't matter what happens to the card,
since the next step will be to perform an electrical reset of the card.
The platform. By "electrical reset", I mean "dropping the #RST pin low
for 200mS". Only the platform can do this.
If it's the platform, I agree with you, but if it's e1000_reset, it might not work because
e1000_reset uses a e1000-specific approach to reset the card.
The driver has to choices: it can ask for the electrical reset, by
returning PCI_ERS_RESULT_NEED_RESET. But if the driver doesn't need
the electrical reset, then it can return PCI_ERS_RESULT_CAN_RECOVER,
and issue whatever device-specific commands it needs to reset.
I'm not sure if the e1000_reset
will restore the NIC to fresh system power-on state. At least, from the source codes, e1000_reset
couldn't.
I have no idea. That's why this driver issues PCI_ERS_RESULT_NEED_RESET,
which will get it into a fresh system power-on state. Its easy, its
brute-force, it works.
--linas
--
VGER BF report: U 0.5
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