linux-kernel - Re: [v2] PCI: imx: make msi work without pcieportbus

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Message-ID: <1544695636.3137.27.camel@pengutronix.de>
Date:   Thu, 13 Dec 2018 11:07:16 +0100
From:   Lucas Stach <l.stach@...gutronix.de>
To:     Richard Zhu <hongxing.zhu@....com>,
        "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
        "lorenzo.pieralisi@....com" <lorenzo.pieralisi@....com>,
        "andrew.smirnov@...il.com" <andrew.smirnov@...il.com>
Cc:     "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [v2] PCI: imx: make msi work without pcieportbus

Am Donnerstag, den 13.12.2018, 09:57 +0000 schrieb Richard Zhu:
> Hi Lucas:
> 
> > -----Original Message-----
> > > > From: Lucas Stach [mailto:l.stach@...gutronix.de]
> > Sent: 2018年12月13日 17:19
> > > > > > To: Richard Zhu <hongxing.zhu@....com>; bhelgaas@...gle.com;
> > lorenzo.pieralisi@....com; andrew.smirnov@...il.com
> > > > > > Cc: linux-pci@...r.kernel.org; linux-arm-kernel@...ts.infradead.org;
> > linux-kernel@...r.kernel.org
> > Subject: Re: [v2] PCI: imx: make msi work without pcieportbus
> > 
> > Hi Richard,
> > 
> > Am Donnerstag, den 13.12.2018, 08:02 +0000 schrieb Richard Zhu:
> > > MSI_EN of iMX PCIe RC would be asserted when PCIEPORTBUS driver is
> > > selected.
> > > Thus, the MSI works fine on iMX PCIe before.
> > > Assert it unconditionally when MSI is supported.
> > > Otherwise, the MSI wouldn't be triggered although the EP is present
> > > and the MSIs are assigned.
> > 
> > Thanks for digging into this issue. This seems like the right way forward.
> > However, did you test this with devices using legacy IRQs?
> > I.e. booting with "nomsi" on the kernel command line to see if legacy IRQs still
> > work if this bit is set, or if we need to avoid setting this when the user
> > explicitly requests to disable MSIs?
> > 
> > Regards,
> > Lucas
> > 
> 
> [Richard Zhu] Thanks for your review.
> The Legacy INTx is broken.
> The MSI_EN bit shouldn't be asserted when the user explicitly requests to disable MSIs.

Okay, so this patch should be extended with a check for
pci_msi_enabled() to see if the user explicitly want legacy IRQs.

> BTW, regarding to Baruch's comments, it seems that all the (IS_ENABLED(CONFIG_PCI_MSI) check in
>  the dwc host drivers are not required anymore, since the depends on PCI_MSI_IRQ_DOMAIN, right?

That's correct. This is mostly a historical artifact from the time when
 we were able to build without MSI support. Those checks could be
cleaned up now that we depend on the MSI options.

Regards,
Lucas