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Message-ID: <CAMxnaaVfpJCW7e-b80y4wmVWcRDK5t7qY+pNn71CsLPRN2ojnA@mail.gmail.com>
Date: Sat, 8 Mar 2014 10:55:23 +0100
From: Andreas Noever <andreas.noever@...il.com>
To: Bjorn Helgaas <bhelgaas@...gle.com>
Cc: Yinghai Lu <yinghai@...nel.org>,
"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
On Sat, Mar 8, 2014 at 2:04 AM, Bjorn Helgaas <bhelgaas@...gle.com> wrote:
> [+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.
Just a quick note: With pci_intx_for_msi removed no hotplug events are
ever delivered. Everything else still works though. So it is either a
problem specific to Thunderbolt bridges or maybe it just affects
hotplug (and PME?) interrupts.
I also attempted booting with pcie_hp=nomsi and now everything works.
Interestingly pciehp now also gets an interrupt from 09 (event though
that card has just been removed). I suspect this is just pciehp not
noticing that it itself is gone.
pciehp 0000:06:03.0:pcie24: Card not present on Slot(3-1)
pciehp 0000:09:00.0:pcie24: Latch open on Slot(9)
pciehp 0000:09:00.0:pcie24: Button pressed on Slot(9)
pciehp 0000:09:00.0:pcie24: Card present on Slot(9)
pciehp 0000:09:00.0:pcie24: Power fault on slot 9
pciehp 0000:09:00.0:pcie24: Power fault bit 0 set
pciehp 0000:09:00.0:pcie24: PCI slot #9 - powering on due to button press.
pciehp 0000:09:00.0:pcie24: unloading service driver pciehp
pciehp 0000:09:00.0:pcie24: Link Training Error occurs
pciehp 0000:09:00.0:pcie24: Failed to check link status
> 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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