Re: Questions about pci configuration and the mpt(4) driver

[David Young <dyoung%pobox.com@localhost>]

On Sat, Nov 17, 2012 at 02:18:18AM -0800, Brian Buhrow wrote:
>       Hello.  I've been working on an issue with the mpt(4) driver, the
> driver for the LSI Fusion SCSI controller cards and raid cards.  In the
> process of working through the issue, I've discovered that the mpt(4)
> driver is very fragile if the need to reset the hardware arises.  In
> particular, if a hardware reset is done, all of the pci configuration
> registers get zorched, causing interrupt handling to fail and requests to
> get stuck in the driver and hardware's queue.

When does the need for a reset arise?  Is the cause a driver bug or a
hardware/firmware bug?

It sounds to me like you should detach the device (perhaps resetting
in the final stages of the detachment---i.e., before unmapping the
registers) and re-attach it.

Since detachment ordinarily loses all of the software state, you may
need to stash the outstanding requests somewhere that the re-attached
device can find them.

Dave

> I've been looking for
> examples of how to reset the PCI registers after such a reset, but neither
> the OpenBSD or FreeBSD drivers offer a clue.  All BSD drivers I've looked
> at lament the problem, but none provide a solution.  I've considered
> extracting the PCI initialization process from the mpt_pci_attach() routine
> into a separate function that can be called at any time while things are
> running, but there must be a reason this hasn't been done already and why I
> don't see any examples that look obvious to me of any drivers that do this.
> Is it safe to call pci_intr_disestablish() and pci_intr_establish() during
> the course of normal multi-user operation for a particular driver as a
> means of re-attaching interrupts to a device that's forgotten how to
> generate them?  Are there any examples of drivers that do a complete reset
> of the hardware, including pci and pci interrupt settings while continuing
> to operate in multi-user mode?
> -thanks
> -Brian
> 

-- 
David Young
dyoung%pobox.com@localhost    Urbana, IL    (217) 721-9981