Re: [PATCH v2 05/27] arm: pci: add a align_resource hook

[Thomas Petazzoni <thomas.petazzoni@free-electrons.com>]

Dear Arnd Bergmann,

On Wed, 30 Jan 2013 09:46:53 +0000, Arnd Bergmann wrote:
> On Wednesday 30 January 2013, Jason Gunthorpe wrote:
> > > But we normally only assign a 64 KB I/O window to each PCI host bridge.
> > > Requiring PCI bridges to be space 64 KB apart would mean that we cannot
> > > actually support bridges at all.
> > 
> > The PCI resource code uses full 32 bit integers when it handles IO
> > addresses, so this actually does sort of work out.
> 
> However, we only reserve 1 MB (I think) virtual address window for all
> I/O spaces of all PCI domains combined, at a fixed location (0xfee00000).
> This means we can have at most 16 such windows at run-time. That can
> be changed if necessary, but it seems like overkill when in practice
> you only need a few bytes at most.

I am not sure where this 0xfee00000 address comes from, but in my case
(and I think in the Tegra PCI driver as well), we tell the Linux PCI
core from which addresses the I/O ranges should be allocated. In my DT,
I have:

                        ranges = <0x00000800 0 0xd0040000 0xd0040000 0 0x00002000   /* port 0.0 registers */
                                  0x00004800 0 0xd0042000 0xd0042000 0 0x00002000   /* port 2.0 registers */
                                  0x00001000 0 0xd0044000 0xd0044000 0 0x00002000   /* port 0.1 registers */
                                  0x00001800 0 0xd0048000 0xd0048000 0 0x00002000   /* port 0.2 registers */
                                  0x00002000 0 0xd004C000 0xd004C000 0 0x00002000   /* port 0.3 registers */
                                  0x00002800 0 0xd0080000 0xd0080000 0 0x00002000   /* port 1.0 registers */
                                  0x00005000 0 0xd0082000 0xd0082000 0 0x00002000   /* port 3.0 registers */
                                  0x00003000 0 0xd0084000 0xd0084000 0 0x00002000   /* port 1.1 registers */
                                  0x00003800 0 0xd0088000 0xd0088000 0 0x00002000   /* port 1.2 registers */
                                  0x00004000 0 0xd008C000 0xd008C000 0 0x00002000   /* port 1.3 registers */
                                  0x81000000 0 0          0xc0000000 0 0x00100000   /* downstream I/O */
                                  0x82000000 0 0          0xc1000000 0 0x08000000>; /* non-prefetchable memory */

And then, the Marvell PCI driver gets the "downstream I/O" range,
parses it into a "struct resource", and then does (where &pcie->io is
the struct resource into which we parsed the "downstream I/O" range):

        pci_add_resource_offset(&sys->resources, &pcie->io, sys->io_offset);
	[...]
	pci_ioremap_io(nr * SZ_64K, pcie->io.start);

And it works just fine, I get my I/O ranges allocated at 0xc0000000 for
the first device, 0xc0010000 (i.e base address + 64KB) for the second
device, etc.

The Tegra PCI driver does exactly the same (I shamelessly copied what
Thierry has done).

I somehow have the feeling that we are looking for problems that simply
don't exist...

Best regards,

Thomas
-- 
Thomas Petazzoni, Free Electrons
Kernel, drivers, real-time and embedded Linux
development, consulting, training and support.
http://free-electrons.com