linux-kernel - Re: [PATCH] PCI: tegra: Use PCI_CONF1_EXT

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Message-ID: <Y00HiWT+N6Fo9KVD@lpieralisi>
Date:   Mon, 17 Oct 2022 09:43:05 +0200
From:   Lorenzo Pieralisi <lpieralisi@...nel.org>
To:     Jon Hunter <jonathanh@...dia.com>
Cc:     Pali Rohár <pali@...nel.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Rob Herring <robh@...nel.org>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Vidya Sagar <vidyas@...dia.com>, linux-tegra@...r.kernel.org,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] PCI: tegra: Use PCI_CONF1_EXT_ADDRESS() macro

On Tue, Oct 11, 2022 at 05:47:50PM +0100, Jon Hunter wrote:
> 
> On 11/10/2022 17:16, Pali Rohár wrote:
> 
> ...
> 
> > I see, this is stupid mistake. PCIe config read and write operations
> > needs to be 4-byte aligned, so normally it is done by calculating 4-byte
> > aligned base address and then using appropriate cpu load/store
> > instruction to access just defined size/offset of 4-byte config space
> > register.
> > 
> > pci-tegra.c is using common helper functions pci_generic_config_read()
> > and pci_generic_config_write(), which expects final address with offset,
> > and not 4-byte aligned address.
> > 
> > I'm not sure what should be the proper fix, but for me it looks like
> > that pci_generic_config_read() and pci_generic_config_write() could be
> > adjusted to handle it.
> > 
> > In any case, above patch is a regressions and I see there two options
> > for now:
> > 
> > 1) Reverting that patch
> > 
> > 2) Adding "offset |= where & 0x3;" after the PCI_CONF1_EXT_ADDRESS()
> >     macro to set also lower 2 bits of accessed register.
> > 
> > Jon, Lorenzo, what do you think? Could you test if 2) is working fine?
> 
> 
> I tested 'offset |= where & 0xff' which is essentially the same as the above
> and that is working and so I am sure that the above works too. However, I do
> wonder if reverting is simpler because we already have a '&
> ~PCI_CONF1_ENABLE' and now adding '| where & 0x3' seems to diminish the
> value of this change.

Hi Jon,

it is unfortunate but I think we should proceed with a revert, please
send it and I shall ask Bjorn to send it for one of the upcoming -rcX.

Thanks,
Lorenzo