linux-kernel - Re: [PATCH v3 09/10] iommu/dart: Exclude MSI doorbell from PCIe device IOVA range

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Message-ID: <87h7ejbjq9.wl-maz@kernel.org>
Date:   Fri, 17 Sep 2021 11:05:18 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Alyssa Rosenzweig <alyssa@...enzweig.io>
Cc:     devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-pci@...r.kernel.org, Bjorn Helgaas <bhelgaas@...gle.com>,
        Rob Herring <robh+dt@...nel.org>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Stan Skowronek <stan@...ellium.com>,
        Mark Kettenis <kettenis@...nbsd.org>,
        Sven Peter <sven@...npeter.dev>,
        Hector Martin <marcan@...can.st>,
        Robin Murphy <Robin.Murphy@....com>, kernel-team@...roid.com
Subject: Re: [PATCH v3 09/10] iommu/dart: Exclude MSI doorbell from PCIe device IOVA range

On Mon, 13 Sep 2021 19:55:53 +0100,
Alyssa Rosenzweig <alyssa@...enzweig.io> wrote:
> 
> > +config PCIE_APPLE_MSI_DOORBELL_ADDR
> > +	hex
> > +	default 0xfffff000
> > +	depends on PCIE_APPLE
> > +
> >  config PCIE_APPLE
> >  	tristate "Apple PCIe controller"
> >  	depends on ARCH_APPLE || COMPILE_TEST
> > diff --git a/drivers/pci/controller/pcie-apple.c b/drivers/pci/controller/pcie-apple.c
> > index 1ed7b90f8360..76344223245d 100644
> > --- a/drivers/pci/controller/pcie-apple.c
> > +++ b/drivers/pci/controller/pcie-apple.c
> > @@ -120,8 +120,10 @@
> >   * The doorbell address is set to 0xfffff000, which by convention
> >   * matches what MacOS does, and it is possible to use any other
> >   * address (in the bottom 4GB, as the base register is only 32bit).
> > + * However, it has to be excluded from the the IOVA range, and the
> > + * DART driver has to know about it.
> >   */
> > -#define DOORBELL_ADDR			0xfffff000
> > +#define DOORBELL_ADDR		CONFIG_PCIE_APPLE_MSI_DOORBELL_ADDR
> 
> I'm unsure if Kconfig is the right place for this. But if it is, these
> hunks should be moved earlier in the series (so the deletion gets
> squashed away of the hardcoded-in-the-C.)

I'd rather not doing that. There is a progression in the series, and
moving the value over to Kconfig is part of that progression.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.