[PATCH 2/2] ARM: imx_v6_v7_defconfig: enable PCI_MSI

[Tim Harvey]

On Wed, Apr 5, 2017 at 5:16 AM, Lucas Stach <l.stach at pengutronix.de> wrote:
> Am Mittwoch, den 05.04.2017, 13:07 +0100 schrieb Joao Pinto:
> [...]
>> >>> Lucas,
>> >>>
>> >>> I feel a bit dumb here for forgetting about this issue and letting it
>> >>> drop, but I've just spent a day debugging an issue with the ath9k
>> >>> wireless driver only to realize it was that the ath9k card and/or
>> >>> driver doesn't support MSI interrupts and thus no longer work on
>> >>> mainline kernels that have MSI enabled. To be honest I'm not sure how
>> >>> many PCIe devices out there can't support MSI because of hardware
>> >>> limitations vs drivers that simply have not implemented it.
>> >>>
>> >>> To make matters worse 3ee803641e76bea76ec730c80dcc64739a9919ff makes
>> >>> it such that you can't disable MSI on the IMX6.
>> >>>
>> >>> Is there some fix you can think of to make the IMX6 PCIe host
>> >>> controller raise an interrupt for cards/drivers that use legacy irq's?
>> >>> If not, then we need to allow MSI to be disabled for IMX6 and default
>> >>> it to disabled for compatibility.
>> >>>
>> >>
>> >> Joao / Jingoo,
>> >>
>> >> (Adding linux-pci to the list to pick up maintainers of other DWC PCIe
>> >> core drivers)
>> >>
>> >> Is Luca's statement that 'legacy IRQs and MSIs can't be used together'
>> >> true in general for the DW PCIe core? If any of the host controllers
>> >> using this core can't support both legacy and MSI irqs together I
>> >> still believe we shouldn't enable/require MSI as it breaks any
>> >> card/driver that only supports legacy interrupts (such as ath9k).
>> >
>> > If there are 2 DW PCIe controllers, one controller can be used for legacy
>> > and another controller can be used for MSI.
>> >
>> > But, I am not sure that one DW PCIe controller can support both MSI device
>> > and legacy interrupt device at the same time.
>> >
>> > To Joao Pinto,
>> > Will you confirm this?
>> >
>>
>> Hi Jingoo,
>> I confirm that if a RC has MSI enable, it won't support legacy interrupts.
>
> Okay, so the only way to solve this in a generic way, that I can see at
> the moment is to defer MSI enable until the downstream device actually
> requests an MSI irq.
>
> Also we need to disable the MSI capability if any bridge device turns up
> during the bus topology scan, as we can have devices with conflicting
> requirements connected to the RC in that case.
>
> I'll cook up some patches to implement this.
>

Lucas,

Any thoughts yet? I'll likely want to backport this to stable although
the restructuring to drivers/pci/dwc and subsequent changes since 4.10
will likely require a re-written patch.

Best regards,

Tim