linux-kernel - Re: [PATCH 2/2] PCI: mediatek: Add controller support for MT7629

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Message-ID: <20181217143247.GK20725@google.com>
Date:   Mon, 17 Dec 2018 08:32:47 -0600
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Jianjun Wang <jianjun.wang@...iatek.com>
Cc:     ryder.lee@...iatek.com, robh+dt@...nel.org,
        lorenzo.pieralisi@....com, matthias.bgg@...il.com,
        linux-pci@...r.kernel.org, mark.rutland@....com,
        devicetree@...r.kernel.org, youlin.pei@...iatek.com,
        linux-kernel@...r.kernel.org, linux-mediatek@...ts.infradead.org,
        honghui.zhang@...iatek.com, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 2/2] PCI: mediatek: Add controller support for MT7629

On Mon, Dec 17, 2018 at 04:19:39PM +0800, Jianjun Wang wrote:
> On Thu, 2018-12-13 at 08:55 -0600, Bjorn Helgaas wrote:
> > On Thu, Dec 06, 2018 at 09:09:13AM +0800, Jianjun Wang wrote:
> > > The read value of BAR0 is 0xffff_ffff, it's size will be calculated as 4GB
> > > in arm64 but bogus alignment values at arm32, the pcie device and devices
> > > behind this bridge will not be enabled. Fix it's BAR0 resource size to
> > > guarantee the pcie devices will be enabled correctly.
> > 
> > So this is a hardware erratum?  Per spec, a memory BAR has bit 0 hardwired
> > to 0, and an IO BAR has bit 1 hardwired to 0.
> 
> Yes, it only works properly on 64bit platform.

I don't understand.  BARs are supposed to work the same regardless of
whether it's a 32- or 64-bit platform.  If this is a workaround for a
hardware defect, please just say that explicitly.

Bjorn