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SubjectRe: [PATCH] PCI: Fix regression in pci_restore_state()
Date
On Monday, April 23, 2012, Bjorn Helgaas wrote:
> On Sun, Apr 15, 2012 at 1:40 PM, Rafael J. Wysocki <rjw@sisk.pl> wrote:
> > On Sunday, April 15, 2012, Linus Torvalds wrote:
> >> On Sun, Apr 15, 2012 at 11:47 AM, Rafael J. Wysocki <rjw@sisk.pl> wrote:
> >> >
> >> > mdelay(10) doesn't really look good either to me in this case, though.
> >>
> >> Oh, I agree. What kind of ass-backwards device actually needs that
> >> kind of crazy delays? It is almost certainly buggy.
> >>
> >> With retries, 10ms delays are totally unacceptable. There's something wrong.
> >>
> >> A single ms *may* be ok.
> >>
> >> Anyway, can you also split the actual "write _one_ register with
> >> retry" into a function of its own? The code looks like crap with those
> >> multiple levels of looping, with conditionals inside them etc. With a
> >> simple helper function, you could change the break into return, and it
> >> would look much better, I bet.
> >
> > Sure. It appears cleaner this way.
> >
> > ---
> > From: Rafael J. Wysocki <rjw@sisk.pl>
> > Subject: PCI: Fix regression in pci_restore_state(), v3
> >
> > Commit 26f41062f28de65e11d3cf353e52d0be73442be1
> >
> > PCI: check for pci bar restore completion and retry
> >
> > attempted to address problems with PCI BAR restoration on systems
> > where FLR had not been completed before pci_restore_state() was
> > called, but it did that in an utterly wrong way.
> >
> > First off, instead of retrying the writes for the BAR registers
> > only, it did that for all of the PCI config space of the device,
> > including the status register (whose value after the write quite
> > obviously need not be the same as the written one). Second, it
> > added arbitrary delay to pci_restore_state() even for systems
> > where the PCI config space restoration was successful at first
> > attempt. Finally, the mdelay(10) it added to every iteration of the
> > writing loop was way too much of a delay for any reasonable device.
> >
> > All of this actually caused resume failures for some devices on
> > the Mikko's system.
> >
> > To fix the regression, make pci_restore_state() only retry the
> > writes for BAR registers and only wait if the first read from
> > the register doesn't return the written value. Additionaly, make
> > it wait for 1 ms, instead of 10 ms, after every failing attempt
> > to write into config space.
> >
> > Reported-by: Mikko Vinni <mmvinni@yahoo.com>
> > Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
> > ---
> > drivers/pci/pci.c | 57 ++++++++++++++++++++++++++++++++++++------------------
> > 1 file changed, 39 insertions(+), 18 deletions(-)
> >
> > Index: linux/drivers/pci/pci.c
> > ===================================================================
> > --- linux.orig/drivers/pci/pci.c
> > +++ linux/drivers/pci/pci.c
> > @@ -967,16 +967,47 @@ pci_save_state(struct pci_dev *dev)
> > return 0;
> > }
> >
> > +static void pci_restore_config_dword(struct pci_dev *pdev, int offset,
> > + u32 saved_val, int retry)
> > +{
> > + u32 val;
> > +
> > + pci_read_config_dword(pdev, offset, &val);
> > + if (val == saved_val)
> > + return;
> > +
> > + for (;;) {
> > + dev_dbg(&pdev->dev, "restoring config space at offset "
> > + "%#x (was %#x, writing %#x)\n", offset, val, saved_val);
> > + pci_write_config_dword(pdev, offset, saved_val);
> > + if (retry-- <= 0)
> > + return;
> > +
> > + pci_read_config_dword(pdev, offset, &val);
> > + if (val == saved_val)
> > + return;
> > +
> > + mdelay(1);
> > + }
> > +}
> > +
> > +static void pci_restore_config_space(struct pci_dev *pdev, int start, int end,
> > + int retry)
> > +{
> > + int index;
> > +
> > + for (index = end; index >= start; index--)
> > + pci_restore_config_dword(pdev, 4 * index,
> > + pdev->saved_config_space[index],
> > + retry);
> > +}
> > +
> > /**
> > * pci_restore_state - Restore the saved state of a PCI device
> > * @dev: - PCI device that we're dealing with
> > */
> > void pci_restore_state(struct pci_dev *dev)
> > {
> > - int i;
> > - u32 val;
> > - int tries;
> > -
> > if (!dev->state_saved)
> > return;
> >
> > @@ -984,24 +1015,14 @@ void pci_restore_state(struct pci_dev *d
> > pci_restore_pcie_state(dev);
> > pci_restore_ats_state(dev);
> >
> > + pci_restore_config_space(dev, 10, 15, 0);
> > /*
> > * The Base Address register should be programmed before the command
> > * register(s)
> > */
> > - for (i = 15; i >= 0; i--) {
> > - pci_read_config_dword(dev, i * 4, &val);
> > - tries = 10;
> > - while (tries && val != dev->saved_config_space[i]) {
> > - dev_dbg(&dev->dev, "restoring config "
> > - "space at offset %#x (was %#x, writing %#x)\n",
> > - i, val, (int)dev->saved_config_space[i]);
> > - pci_write_config_dword(dev,i * 4,
> > - dev->saved_config_space[i]);
> > - pci_read_config_dword(dev, i * 4, &val);
> > - mdelay(10);
> > - tries--;
> > - }
> > - }
> > + pci_restore_config_space(dev, 4, 9, 10);
> > + pci_restore_config_space(dev, 0, 3, 0);
> > +
> > pci_restore_pcix_state(dev);
> > pci_restore_msi_state(dev);
> > pci_restore_iov_state(dev);
>
> I'd feel better about this if there were a way to delay in the FLR
> path instead. If we delay in the restore path, we're only fixing one
> of the many ways config space can be written. Other paths that write
> config space will just silently fail.
>
> The PCIe spec (r3.0, sec 6.6.2) mentions waiting for the "pre-FLR
> value for Completion Timeout," but I don't see anything that looks
> like that in pcie_flr() or pci_af_flr(). Are there any other direct
> ways we can detect when the FLR is complete?

I'm not aware of any.

Thanks,
Rafael


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