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Date: Fri, 7 Mar 2014 18:04:56 -0700
From: Bjorn Helgaas <bhelgaas@...gle.com>
To: Yinghai Lu <yinghai@...nel.org>
Cc: Andreas Noever <andreas.noever@...il.com>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
Rajat Jain <rajatxjain@...il.com>,
"Rafael J. Wysocki" <rjw@...ysocki.net>
Subject: Re: [Bug] PCI: Enable INTx if BIOS left them disabled - triggers
during rescan
[+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@...gle.com> 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;
> }
>
--
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