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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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