Re: [PATCH 06/17] pci: host: pcie-designware: Use *base-mask* for configuring the iATU

Arnd Bergmann
2014-05-13T12:47:25Z

On Tuesday 13 May 2014 18:01:59 Kishon Vijay Abraham I wrote:
> On Thursday 08 May 2014 02:48 PM, Arnd Bergmann wrote:
> > On Thursday 08 May 2014 18:05:11 Jingoo Han wrote:
> >> On Tuesday, May 06, 2014 10:59 PM, Arnd Bergmann wrote:
> >>> On Tuesday 06 May 2014 19:03:52 Kishon Vijay Abraham I 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.
> >>>>
> >>>> Cc: Bjorn Helgaas <bhelgaas-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
> >>>> Cc: Marek Vasut <marex-ynQEQJNshbs@public.gmane.org>
> >>>> Signed-off-by: Kishon Vijay Abraham I <kishon-l0cyMroinI0@public.gmane.org>
> >>>> Acked-by: Jingoo Han <jg1.han-Sze3O3UU22JBDgjK7y7TUQ@public.gmane.org>
> >>>> Acked-by: Mohit Kumar <mohit.kumar-qxv4g6HH51o@public.gmane.org>
> >>>
> >>> Sorry, but NAK.
> >>>
> >>> We have a standard 'dma-ranges' property to handle this, so use it.
> >>>
> >>> See the x-gene PCIe driver patches for an example. Please also talk
> >>> to Santosh about it, as he is implementing generic support for
> >>> parsing dma-ranges in platform devices at the moment.
> >>
> >> Hi Arnd,
> >>
> >> Do you mean the following patch?
> >> http://www.spinics.net/lists/kernel/msg1737725.html
> >>
> >
> > That is the patch Santosh did for platform devices, which is related but not
> > what I meant here. For the PCI inbound window setup, please have a look
> > at https://lkml.org/lkml/2014/3/19/607
>
> Do you think it can be used for *outbound* window setup too? The problem is the
> *ranges* property defines both the pci address and cpu address which should
> have been enough to program the ob translation window, but the hw is designed
> so that the controller sees only the 28 bits. (The most significant 4 bits is
> for the l3 to address the controller).

I'm not following what the problem is. You should always be able to describe
in the inbound window (that is from the CPU perspective) using dma-ranges
and the outbound window using ranges.

If you have a case where the outbound translation is a 256MB (i.e. 28bit)
section of the CPU address space, that could be represented as

ranges = <0x82000000 0 0 0xb0000000 0 0x10000000>;

or

ranges = <0x82000000 0 0xb0000000 0xb0000000 0 0x10000000>;

depending on whether you want the BARs to be programmed using a low
address 0x0-0x0fffffff or an address matching the window
0xb0000000-0xbfffffff.

Arnd
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