linux-kernel - Re: [RFC PATCH RESEND v2] of/pci: Provide support for parsing PCI DT ranges property

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Date:	Fri, 8 Mar 2013 16:39:24 +0000
From:	Andrew Murray <andrew.murray@....com>
To:	Rob Herring <robherring2@...il.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devicetree-discuss@...ts.ozlabs.org" 
	<devicetree-discuss@...ts.ozlabs.org>,
	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
	"rob.herring@...xeda.com" <rob.herring@...xeda.com>,
	Grant Likely <grant.likely@...retlab.ca>,
	Thierry Reding <thierry.reding@...onic-design.de>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	Linus Walleij <linus.walleij@...aro.org>,
	Liviu Dudau <Liviu.Dudau@....com>
Subject: Re: [RFC PATCH RESEND v2] of/pci: Provide support for parsing PCI
 DT ranges property

On Fri, Mar 01, 2013 at 03:13:34PM +0000, Rob Herring wrote:
> On 03/01/2013 06:23 AM, Andrew Murray wrote:
> > This patch factors out common implementations patterns to reduce overall kernel
> > code and provide a means for host bridge drivers to directly obtain struct
> > resources from the DT's ranges property without relying on architecture specific
> > DT handling. This will make it easier to write archiecture independent host bridge
> > drivers and mitigate against further duplication of DT parsing code.
> > 
> > This patch can be used in the following way:
> > 
> > 	struct of_pci_range_iter iter;
> > 	for_each_of_pci_range(&iter, np) {
> > 
> > 		//directly access properties of the address range, e.g.:
> > 		//iter.pci_space, iter.pci_addr, iter.cpu_addr, iter.size or
> > 		//iter.flags
> > 
> > 		//alternatively obtain a struct resource, e.g.:
> > 		//struct resource res;
> > 		//range_iter_fill_resource(iter, np, res);
> > 	}
> > 
> > Additionally the implementation takes care of adjacent ranges and merges them
> > into a single range (as was the case with powerpc and microblaze).
> > 
> > The modifications to microblaze, mips and powerpc have not been tested.
> > 
> > v2:
> >   This follows on from suggestions made by Grant Likely
> >   (marc.info/?l=linux-kernel&m=136079602806328)
> > 
> > Signed-off-by: Andrew Murray <Andrew.Murray@....com>
> > Signed-off-by: Liviu Dudau <Liviu.Dudau@....com>
> > ---
> >  arch/microblaze/pci/pci-common.c |  100 +++++++++++--------------------------
> >  arch/mips/pci/pci.c              |   44 ++++-------------
> >  arch/powerpc/kernel/pci-common.c |   93 ++++++++++-------------------------
> >  drivers/of/address.c             |   54 ++++++++++++++++++++
> >  include/linux/of_address.h       |   30 +++++++++++
> >  5 files changed, 151 insertions(+), 170 deletions(-)
> 
> The thing is that this still leaves pci_process_bridge_OF_ranges
> basically identical for microblaze and powerpc which is really what
> needs to be moved out to common code. Obviously, struct pci_controller
> vs. struct pci_sys_data on ARM is an issue, but they all have
> fundamentally the same data.
> 
> All these common fields should be in a common PCI controller struct.
> Perhaps introducing this with just what you need would work. Depending
> how invasive moving those fields to a new struct is, you could have a
> wrapper that just copies/translates the fields to the arch specific struct.
> 
> There's also things like ioremap of the i/o range. ARM uses a fixed
> virtual address, so we need to do something different. Just returning
> the i/o cpu_addr and moving the ioremap out of this function would solve
> that.

This is my current thinking...

 - Move struct pci_controller from arch/powerpc/include/asm/pci-bridge.h to
   include/linux/pci-bridge and rename (struct pci_controller_generic). Remove
   struct pci_controller from arch/microblaze/include/asm/pci-bridge.h.

   The powerpc struct pci_controller is a superset of the microblaze struct
   pci_controller. Doing this will allow two architectures to share a common
   implementation of a struct pci_controller. #ifdef's can be used to remove
   extra powerpc fields in the structure (they aren't many).

 - Provide a common implementation of pci_process_bridge_OF_range. This would
   use the for_each_of_pci_range macro to populate a struct pci_controller,
   this would remove duplicate code between microblaze and powerpc. The common
   implementation could use a Kconfig option to enable/disable handling the ISA
   hole (for architectures that don't need/want it). The caller can worry
   about ioremap.

 - Other architectures (mips, ARM) could use this common implementation of
   pci_process_bridge_OF_range in the future but at present they can use
   for_each_of_pci_range (as shown in this patch).
   
This reduces duplicated code, gives ARM a means of parsing PCI DT and provides
a starting point for getting ARM's pci_sys_data more inline with powerpc and
microblaze. Perhaps with a common controller structure - other areas of code
can also be factored out - for example functions like
pcibios_setup_phb_resources, etc - these are probably only arch specific due to
their use of the arch specific pci_controller struct.

Do you think this is a sensible direction?

Andrew Murray

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