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

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Date:   Tue, 11 Oct 2022 18:16:38 +0200
From:   Pali Rohár <pali@...nel.org>
To:     Jon Hunter <jonathanh@...dia.com>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        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 Tuesday 11 October 2022 16:42:34 Jon Hunter wrote:
> On 28/09/2022 13:19, Pali Rohár wrote:
> > Simplify pci-tegra.c driver code and use new PCI_CONF1_EXT_ADDRESS() macro
> > for accessing PCI config space.
> > 
> > Signed-off-by: Pali Rohár <pali@...nel.org>
> > ---
> > Please look also at this related patch:
> > https://patchwork.kernel.org/project/linux-pci/patch/20220911113216.14892-1-pali@kernel.org/
> > ---
> >   drivers/pci/controller/pci-tegra.c | 11 +++--------
> >   1 file changed, 3 insertions(+), 8 deletions(-)
> > 
> > diff --git a/drivers/pci/controller/pci-tegra.c b/drivers/pci/controller/pci-tegra.c
> > index 5df90d183526..c9924e75e597 100644
> > --- a/drivers/pci/controller/pci-tegra.c
> > +++ b/drivers/pci/controller/pci-tegra.c
> > @@ -417,13 +417,6 @@ static inline u32 pads_readl(struct tegra_pcie *pcie, unsigned long offset)
> >    * address (access to which generates correct config transaction) falls in
> >    * this 4 KiB region.
> >    */
> > -static unsigned int tegra_pcie_conf_offset(u8 bus, unsigned int devfn,
> > -					   unsigned int where)
> > -{
> > -	return ((where & 0xf00) << 16) | (bus << 16) | (PCI_SLOT(devfn) << 11) |
> > -	       (PCI_FUNC(devfn) << 8) | (where & 0xff);
> > -}
> > -
> >   static void __iomem *tegra_pcie_map_bus(struct pci_bus *bus,
> >   					unsigned int devfn,
> >   					int where)
> > @@ -445,7 +438,9 @@ static void __iomem *tegra_pcie_map_bus(struct pci_bus *bus,
> >   		unsigned int offset;
> >   		u32 base;
> > -		offset = tegra_pcie_conf_offset(bus->number, devfn, where);
> > +		offset = PCI_CONF1_EXT_ADDRESS(bus->number, PCI_SLOT(devfn),
> > +					       PCI_FUNC(devfn), where) &
> > +			 ~PCI_CONF1_ENABLE;
> >   		/* move 4 KiB window to offset within the FPCI region */
> >   		base = 0xfe100000 + ((offset & ~(SZ_4K - 1)) >> 8);
> 
> 
> Our PCIe test on Tegra124 Jetson TK1 is currently failing on -next and
> bisect points to this commit. Looking at bit closer, the problem appears to
> be the PCI_CONF1_REG_MASK which has a value of 0xfc. Before this patch was
> applied a mask of 0xff was applied to the lower 8-bits of 'where' and now it
> is 0xfc. So this does not work for Tegra as it is.
> 
> Let me know if you have any thoughts?
> 
> Jon
> 
> -- 
> nvpublic

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?