linux-kernel - Re: [PATCH] pcie: Add Xilinx PCIe Host Bridge IP driver

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Date:	Tue, 18 Feb 2014 17:35:23 -0700
From:	Jason Gunthorpe <jgunthorpe@...idianresearch.com>
To:	Bjorn Helgaas <bhelgaas@...gle.com>
Cc:	Srikanth Thokala <sthokal@...inx.com>,
	Arnd Bergmann <arnd@...db.de>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	Michal Simek <michal.simek@...inx.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Rob Herring <robh+dt@...nel.org>,
	Grant Likely <grant.likely@...aro.org>,
	linux-arm <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] pcie: Add Xilinx PCIe Host Bridge IP driver

On Tue, Feb 18, 2014 at 02:32:58PM -0700, Bjorn Helgaas wrote:
> [+cc Arnd]
> 
> On Sun, Feb 16, 2014 at 8:33 AM, Srikanth Thokala <sthokal@...inx.com> wrote:
> > This is the driver for Xilinx AXI PCIe Host Bridge Soft IP
> >
> > Signed-off-by: Srikanth Thokala <sthokal@...inx.com>
> > - Rebased on v3.14.0-rc2
> >  .../devicetree/bindings/pci/xilinx-pcie.txt        |   43 +
> >  drivers/pci/host/Kconfig                           |    7 +
> >  drivers/pci/host/Makefile                          |    1 +
> >  drivers/pci/host/pci-xilinx.c                      |  985 ++++++++++++++++++++
> >  4 files changed, 1036 insertions(+)
> >  create mode 100644 Documentation/devicetree/bindings/pci/xilinx-pcie.txt
> >  create mode 100644 drivers/pci/host/pci-xilinx.c
> >
> > diff --git a/Documentation/devicetree/bindings/pci/xilinx-pcie.txt b/Documentation/devicetree/bindings/pci/xilinx-pcie.txt
> > new file mode 100644
> > index 0000000..66a2487
> > +++ b/Documentation/devicetree/bindings/pci/xilinx-pcie.txt
> > @@ -0,0 +1,43 @@
> > +* Xilinx AXI PCIe Root Port Bridge DT description
> > +
> > +Required properties:
> > +- #address-cells: Address representation for root ports, set to <3>
> > +- #size-cells: Size representation for root ports, set to <2>
> > +- compatible: Should contain "xlnx,axi-pcie-1.00.a"
> > +- reg: Should contain AXI PCIe registers location and length
> > +- interrupts: Should contain AXI PCIe interrupt
> > +- ranges: ranges for the PCI memory regions
> > +       Please refer to the standard PCI bus binding document for a more
> > +       detailed explanation
> > +- xlnx,axibar-num: Number of memory regions configured in the hardware,
> > +       maximum being three which is configurable in the hardware.
> > +- xlnx,include-rc: Root Port (=1) or End Point (=0)
> > +- xlnx,pciebar2axibar-0: Translation address from PCIe to AXI
> > +       Only one PCIe BAR is applicable in Root port mode, it can be
> > +       either 32/64-bit. If it is 64-bit BAR, lower 32 bits are present
> > +       in 'xlnx,pciebar2axibar-0' and Upper 32 bits in 'xlnx,pciebar2
> > +       axibar-1'. And if it is 32-bit BAR, only 'xlnx,pciebar2axibar-0'
> > +       is valid
> > +
> > +Optional properties
> > +- xlnx,pciebar-as: PCIe BAR aperture size is 32 (=0) or 64-bit (=1).
> > +- xlnx,pciebar2axibar-1: Translation address from PCIe to AXI, contains
> > +       upper 32 bits if PCIe BAR size is 64-bit. When xlnx,pciebar-as
> > +       is set, this is a required property and should contain a valid
> > +       value (other than FF's)
> 
> I hardly know anything about DT, but xlnx,pciebar2axibar-0,
> xlnx,pciebar-as, and xlnx,pciebar2axibar-1 look strange to me.  Is
> that really the DT way of dealing with 32/64-bit BARs and host bridge
> address translation?  I don't see similar things in the other files in
> Documentation/devicetree/bindings/pci/, even though some of the other
> drivers/pci/host/*.c files do use pci_add_resource_offset(), which
> indicates that they support address translation.

I agree Bjorn.

These should use the standard ranges mechanism for translations and
apertures.

Also, IMHO, only root ports should be supported in a host bridge
driver. A PCI end point is something entirely different.

I think with those two observations all the xlnx properties should go
away.

Thanks,
Jason
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