linux-kernel - Re: [PATCH v2 4/4] pci: Add support for creating a generic host

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Date:	Thu, 27 Feb 2014 17:45:24 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	linaro-kernel@...ts.linaro.org
Cc:	Liviu Dudau <Liviu.Dudau@....com>,
	linux-pci <linux-pci@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 4/4] pci: Add support for creating a generic host_bridge from device tree

On Thursday 27 February 2014 16:20:03 Liviu Dudau wrote:
> On Thu, Feb 27, 2014 at 03:58:41PM +0000, Arnd Bergmann wrote:
> > On Thursday 27 February 2014 14:13:22 Liviu Dudau wrote:
> > > 
> > > It is useful for host bridge drivers as this is the only place where we store
> > > the physical CPU address for the IO range. This is then needed when setting up the
> > > translation registers. Also used when calling the pci_ioremap_io function that I'm
> > > introducing in the AArch64 patches.
> > 
> > I don't understand what translation windows you are talking about. Is this
> > about how the PCI spaces are mapped into the CPU address space? If so, I
> > would strongly recommend to have this handled by the boot loader before
> > calling into the kernel. For ARM32, we have a lot of embedded systems
> > that require the PCI host driver to set up those windows, but actually
> > it would be much better to just have the firmware tell us what the setup
> > is and that use that.
> 
> The AXI to PCI bridge that I'm using has a set of registers for doing address translation.
> When it sees an AXI translation that matches the programmed translation window will
> convert it into a PCI write using the PCI address base written in that translation window.
> In other words you basically program the DT range into those address translation registers
> and the bridge does the AXI to PCI conversion for you.

Right. That should definitely be done in the boot loader
before Linux is started.


	Arnd
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