On Wed, Jun 01, 2016 at 05:41:53PM +0200, Arnd Bergmann wrote:

On Wednesday, June 1, 2016 10:09:29 AM CEST Bjorn Helgaas wrote:

quoted

Hi Arnd,

On Wed, Jun 01, 2016 at 02:31:22PM +0200, Arnd Bergmann wrote:

quoted

A lot of PCI host bridges require different methods for initiating
type 0 and type 1 config space accesses, leading to duplication of
code.

This adds support for the two different kinds at the pci_ops
level, with the newly added map_bridge/read_bridge/write_bridge
operations for type 1 accesses.

When these are not set, we fall back to the regular map_bus/read/write
operations, so all existing drivers keep working, and bridges that
have identical operations continue to only require one set.

This adds new config accessor functions to struct pci_ops and makes
the callers responsible for figuring out which one to use.  The
benefit is to reduce code duplication in some host bridge drivers
(DesignWare and MVEBU so far).

From a design perspective, I'm not comfortable with moving this burden
from the host bridge drivers to the callers of the config accessors.

...

Maybe we can simply change them to use the normal API and come up with
a way to make the pci_ops harder to misuse? Would it make you feel better
if we also renamed .read/.write into .read_type0/.write_type0 or something
like that?

I'm trying to get a better feel for the tradeoff here.  It seems like
an API complication vs. code duplication.

I don't really think the callers should have to figure out which
accessor to use.  How much of a benefit do we really gain by
complicating the callers?  We've managed for quite a few years with
the current scheme, and it seems like only a couple new ARM platforms
would benefit.

Bjorn