linux-kernel - Re: [PATCH] of: Support a PCI device that is compatible with 'simple-bus'

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Date:	Mon, 04 Mar 2013 10:55:36 +0800
From:	Grant Likely <grant.likely@...retlab.ca>
To:	Jason Gunthorpe <jgunthorpe@...idianresearch.com>
Cc:	linux-kernel@...r.kernel.org, devicetree-discuss@...ts.ozlabs.org,
	Rob Herring <rob.herring@...xeda.com>
Subject: Re: [PATCH] of: Support a PCI device that is compatible with 'simple-bus'

On Wed, 19 Dec 2012 12:18:00 -0700, Jason Gunthorpe <jgunthorpe@...idianresearch.com> wrote:
> On Wed, Dec 19, 2012 at 12:54:51PM +0000, Grant Likely wrote:
> > In both cases, the type of transfer is encoded by the BAR address and
> > does not get exposed to the child device. Exposing the PCI flags into
> > the child bus(es) really isn't a very good idea because they don't make
> > sense in that context. It may seem expedient, but it will be fragile.
> 
> Well, it makes as much sense as for a PCI driver - each of the three
> transfer types has different coding requirements in the driver, so
> each of the three type must be kept separate.
> 
> I haven't looked super closely at this, but the basic desire is to
> have IORESOURCE_PREFETCH tagged on the struct resource that reaches
> the platform driver. 'get_flags' for a non-PCI addresses scheme always
> returns IORESOURCE_MEM, and translating through a ranges doesn't
> appear to fix that. This is where 3dw is desirable because it uses a
> get_flags that understands the three resource types.

We could possibly change the ranges translation code to pick up
IORESOURCE_PREFETCH when a translation crosses a PREFETCH bar. That
would also ensure that child nodes don't have to keep the flags field
consistent with the ranges mapping.

g.
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