Re: [v6] PCI: imx: make msi work without CONFIG_PCIEPORTBUS=y

[Trent Piepho <tpiepho@impinj.com>]

On Fri, 2018-12-21 at 04:33 +0000, Richard Zhu wrote:
> The MSI Enable bit in the MSI Capability (PCIe r4.0, sec 7.7.1.2)
> controls whether a Function can request service using MSI.
> 
> i.MX6 Root Ports implement the MSI Capability and may use MSI to
> request service for events like PME, hotplug, AER, etc.  In
> addition, on i.MX6, the MSI Enable bit controls delivery of MSI
> interrupts from components below the Root Port.
> 
> Prior to commit f3fdfc4ac3a2 ("PCI: Remove host driver Kconfig
> selection
> of CONFIG_PCIEPORTBUS"), enabling CONFIG_PCI_IMX6 automatically also
> enabled CONFIG_PCIEPORTBUS, and when portdrv claimed the Root Ports,
> it set the MSI Enable bit so it could use PME, hotplug, AER, etc.
> As a side effect, that also enabled delivery of MSI interrupts from
> downstream components.
> 
> After f3fdfc4ac3a2, the imx6q-pcie driver can operate without
> portdrv, but that means imx6q-pcie must set the MSI Enable bit
> itself if downstream components use MSI.
> 
> Fixes: f3fdfc4ac3a2 ("PCI: Remove host driver Kconfig selection of
> CONFIG_PCIEPORTBUS")
> 
> Signed-off-by: Richard Zhu <hongxing.zhu@nxp.com>
> Reviewed-by: Lucas Stach <l.stach@pengutronix.de>
> Tested-by: Sven Van Asbroeck <TheSven73@googlemail.com>
> Acked-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>

Tested on IMX7d, allows MSI to work without enabling PCIEPORTBUS, which
fails without this patch.