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

[Lucas Stach]

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.

Regards,
Lucas