linux-kernel - Re: [v6] PCI: imx: make msi work without CONFIG

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Message-ID: <1545853546.7501.10.camel@impinj.com>
Date:   Wed, 26 Dec 2018 19:45:47 +0000
From:   Trent Piepho <tpiepho@...inj.com>
To:     "l.stach@...gutronix.de" <l.stach@...gutronix.de>,
        "lorenzo.pieralisi@....com" <lorenzo.pieralisi@....com>,
        "hongxing.zhu@....com" <hongxing.zhu@....com>,
        "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
        "andrew.smirnov@...il.com" <andrew.smirnov@...il.com>,
        "TheSven73@...glemail.com" <TheSven73@...glemail.com>
CC:     "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>
Subject: Re: [v6] PCI: imx: make msi work without CONFIG_PCIEPORTBUS=y

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@....com>
> Reviewed-by: Lucas Stach <l.stach@...gutronix.de>
> Tested-by: Sven Van Asbroeck <TheSven73@...glemail.com>
> Acked-by: Lorenzo Pieralisi <lorenzo.pieralisi@....com>

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