[+cc Rafael] On Fri, Mar 07, 2014 at 11:39:48AM -0800, Yinghai Lu wrote: > On Fri, Mar 7, 2014 at 8:45 AM, Bjorn Helgaas <bhelgaas@xxxxxxxxxx> wrote: > > > > I opened a bugzilla report at https://bugzilla.kernel.org/show_bug.cgi?id=71691 > > > > It seems like clearing DisINTx has some effect on MSI. I don't see > > anything in the spec that would suggest this (I'm looking at the PCIe > > r3.0 spec, sec 7.5.1.1). > > > > Can somebody point out a connection between DisINTx and MSI? If not, > > maybe we'll need some sort of quirk to deal with this. > > I had different impression: if you disable INTx in some chipset, MSI will not > work anymore. > > so we have > > static void pci_intx_for_msi(struct pci_dev *dev, int enable) > { > if (!(dev->dev_flags & PCI_DEV_FLAGS_MSI_INTX_DISABLE_BUG)) > pci_intx(dev, enable); > } > > and have quirks for ati and broadcom chip to set that FLAG. Setting INTX_DISABLE on some chipsets seems to disable MSI, and that behavior seems to be a hardware defect (see ba698ad4b7e4 "PCI: Add quirk for devices which disable MSI when INTX_DISABLE is set.") Andreas has a device where *clearing* INTX_DISABLE seems to disable MSI. Do you think that's also a hardware defect? If it's not a defect, is there something in the spec that explains why that happens? > regarding the regression: i would suggest move out > do_pci_enable_intx() from re-enable path. Today we have this: pcie_portdrv_probe pci_enable_device # clears INTX_DISABLE pci_enable_msi # sets INTX_DISABLE pciehp_configure_device pci_reenable_device # clears INTX_DISABLE again This is clearly not the intent; we set INTX_DISABLE when MSI was enabled, then we clear it again later even though MSI is still enabled. Maybe we should just leave INTX_DISABLE alone if (dev->msi_enabled || dev->msix_enabled). pci_reenable_device() is also used in the device resume path. I don't know what should happen there. But I'm curious about why we set INTX_DISABLE when enabling MSI/MSI-X in the first place. Per the PCI 3.0 spec, sec 6.8.3.3: While enabled for MSI or MSI-X operation, a function is prohibited from using its INTx# pin (if implemented) to request service (MSI, MSI-X, and INTx# are mutually exclusive). This suggests that we might not need to touch INTX_DISABLE when we're enabling MSI/MSI-X. I looked at these commits related to it: ba698ad4b7e4 PCI: Add quirk for devices which disable MSI when INTX_DISABLE is set. b1cbf4e4dddd msi: fix up the msi enable/disable logic 1769b46a3ed9 PCI MSI: always toggle legacy-INTx-enable bit upon MSI entry/exit 986162d3239a ia32 Message Signalled Interrupt support and none of them mentions a problem that requires us to set INTX_DISABLE. It's possible that we're causing ourselves trouble by being overly defensive. I wonder what would happen if we stopped fiddling with it in the MSI/MSI-X paths, e.g., something like this (just as an experiment, of course): diff --git a/drivers/pci/msi.c b/drivers/pci/msi.c index 7a0fec6ce571..9ef7bd608add 100644 --- a/drivers/pci/msi.c +++ b/drivers/pci/msi.c @@ -442,8 +442,6 @@ static struct msi_desc *alloc_msi_entry(struct pci_dev *dev) static void pci_intx_for_msi(struct pci_dev *dev, int enable) { - if (!(dev->dev_flags & PCI_DEV_FLAGS_MSI_INTX_DISABLE_BUG)) - pci_intx(dev, enable); } static void __pci_restore_msi_state(struct pci_dev *dev) If we did that, INTX_DISABLE would be cleared by the first pci_enable_device() and pci_reenable_device() wouldn't do anything, leaving it cleared. The resulting state (cleared) would be the same, but the transitions would be gone, and maybe those are important. The thing I don't like about the patch below is that it's magical: the code doesn't have any obvious connection with the problem. How would one deduce that this is necessary, or explain why it's necessary? A changelog like "this makes things work" is not really very useful. If we make a change like this, it needs to be connected with MSI/MSI-X somehow so a reader can figure out why we twiddle INTX_DISABLE in the enable path but not the reenable path. Bjorn > diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c > index 5a24cb3..92718c9 100644 > --- a/drivers/pci/pci.c > +++ b/drivers/pci/pci.c > @@ -1190,11 +1190,22 @@ int __weak pcibios_enable_device(struct > pci_dev *dev, int bars) > return pci_enable_resources(dev, bars); > } > > +static void do_pci_enable_intx(struct pci_dev *dev) > +{ > + u8 pin; > + pci_read_config_byte(dev, PCI_INTERRUPT_PIN, &pin); > + if (pin) { > + pci_read_config_word(dev, PCI_COMMAND, &cmd); > + if (cmd & PCI_COMMAND_INTX_DISABLE) > + pci_write_config_word(dev, PCI_COMMAND, > + cmd & ~PCI_COMMAND_INTX_DISABLE); > + } > +} > + > static int do_pci_enable_device(struct pci_dev *dev, int bars) > { > int err; > u16 cmd; > - u8 pin; > > err = pci_set_power_state(dev, PCI_D0); > if (err < 0 && err != -EIO) > @@ -1204,14 +1215,6 @@ static int do_pci_enable_device(struct pci_dev > *dev, int bars) > return err; > pci_fixup_device(pci_fixup_enable, dev); > > - pci_read_config_byte(dev, PCI_INTERRUPT_PIN, &pin); > - if (pin) { > - pci_read_config_word(dev, PCI_COMMAND, &cmd); > - if (cmd & PCI_COMMAND_INTX_DISABLE) > - pci_write_config_word(dev, PCI_COMMAND, > - cmd & ~PCI_COMMAND_INTX_DISABLE); > - } > - > return 0; > } > > @@ -1287,6 +1290,8 @@ static int pci_enable_device_flags(struct > pci_dev *dev, unsigned long flags) > err = do_pci_enable_device(dev, bars); > if (err < 0) > atomic_dec(&dev->enable_cnt); > + else > + do_pci_enable_intx(dev); > return err; > } > diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c > index 5a24cb3..92718c9 100644 > --- a/drivers/pci/pci.c > +++ b/drivers/pci/pci.c > @@ -1190,11 +1190,22 @@ int __weak pcibios_enable_device(struct pci_dev *dev, int bars) > return pci_enable_resources(dev, bars); > } > > +static void do_pci_enable_intx(struct pci_dev *dev) > +{ > + u8 pin; > + pci_read_config_byte(dev, PCI_INTERRUPT_PIN, &pin); > + if (pin) { > + pci_read_config_word(dev, PCI_COMMAND, &cmd); > + if (cmd & PCI_COMMAND_INTX_DISABLE) > + pci_write_config_word(dev, PCI_COMMAND, > + cmd & ~PCI_COMMAND_INTX_DISABLE); > + } > +} > + > static int do_pci_enable_device(struct pci_dev *dev, int bars) > { > int err; > u16 cmd; > - u8 pin; > > err = pci_set_power_state(dev, PCI_D0); > if (err < 0 && err != -EIO) > @@ -1204,14 +1215,6 @@ static int do_pci_enable_device(struct pci_dev *dev, int bars) > return err; > pci_fixup_device(pci_fixup_enable, dev); > > - pci_read_config_byte(dev, PCI_INTERRUPT_PIN, &pin); > - if (pin) { > - pci_read_config_word(dev, PCI_COMMAND, &cmd); > - if (cmd & PCI_COMMAND_INTX_DISABLE) > - pci_write_config_word(dev, PCI_COMMAND, > - cmd & ~PCI_COMMAND_INTX_DISABLE); > - } > - > return 0; > } > > @@ -1287,6 +1290,8 @@ static int pci_enable_device_flags(struct pci_dev *dev, unsigned long flags) > err = do_pci_enable_device(dev, bars); > if (err < 0) > atomic_dec(&dev->enable_cnt); > + else > + do_pci_enable_intx(dev); > return err; > } > -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
