linux-kernel - Re: [PATCH v2 04/18] PCI: designware: use untranslated address while programming ATU

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Date:	Fri, 20 Jun 2014 20:54:39 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Rob Herring <robherring2@...il.com>
Cc:	Kishon Vijay Abraham I <kishon@...com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	linux-omap <linux-omap@...r.kernel.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Marek Vasut <marex@...x.de>, Tony Lindgren <tony@...mide.com>,
	Mohit Kumar <mohit.kumar@...com>,
	Jingoo Han <jg1.han@...sung.com>,
	Jason Gunthorpe <jgunthorpe@...idianresearch.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>
Subject: Re: [PATCH v2 04/18] PCI: designware: use untranslated address while programming ATU

On Friday 20 June 2014 12:45:46 Rob Herring wrote:
> On Thu, May 29, 2014 at 1:38 AM, Kishon Vijay Abraham I <kishon@...com> wrote:
> > In DRA7, the cpu sees 32bit address, but the pcie controller can see only 28bit
> > address. So whenever the cpu issues a read/write request, the 4 most
> > significant bits are used by L3 to determine the target controller.
> > For example, the cpu reserves 0x2000_0000 - 0x2FFF_FFFF for PCIe controller but
> > the PCIe controller will see only (0x000_0000 - 0xFFF_FFF). So for programming
> > the outbound translation window the *base* should be programmed as 0x000_0000.
> > Whenever we try to write to say 0x2000_0000, it will be translated to whatever
> > we have programmed in the translation window with base as 0x000_0000.
> >
> > This is needed when the dt node is modelled something like below
> > axi {
> >         compatible = "simple-bus";
> >         #size-cells = <1>;
> >         #address-cells = <1>;
> >         ranges = <0x0        0x20000000 0x10000000 // 28-bit bus
> >                   0x51000000 0x51000000 0x3000>;
> >         pcie@...00000 {
> >                 reg = <0x1000 0x2000>, <0x51002000 0x14c>, <0x51000000 0x2000>;
> >                 reg-names = "config", "ti_conf", "rc_dbics";
> >                 #address-cells = >;
> >                 #size-cells = <2>;
> >                 ranges = <0x81000000 0 0          0x03000 0 0x00010000
> >                           0x82000000 0 0x20013000 0x13000 0 0xffed000>;
> >         };
> > };
> >
> > Here the CPU address for configuration space is 0x20013000 and the controller
> > address for configuration space is 0x13000. The controller address should be
> > used while programming the ATU (in order for translation to happen properly in
> > DRA7xx).
> 
> This talks about config space, but the ranges field is PCI memory
> space. Also, does this actually work because I though Linux expects
> memory BARs to be 1MB aligned.

Good point about the alignment.

Actually both the config space and memory space are set up through the
intermediate ranges of the parent bus.

> Getting the controller offset should work whether you specify the
> address as 0x13000 with translation or the absolute address
> 0x20013000. In other words, the driver should know how many bits to
> mask off to get the offset.

That's what the first version of the patch did, and I didn't like that
because the masking is not actually a property of the controller, but
it's based on how the controller is connected to the parent bus, in this
case by using a narrower connection. We can describe the connection just
fine using standard DT properties and I think we should.

	Arnd
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