Re: [PATCH v2 2/4] PCI: iproc: Add Broadcom iProc PCIe driver

From: Ray Jui
Date: Mon Dec 15 2014 - 19:28:35 EST

On 12/15/2014 1:37 PM, Arnd Bergmann wrote:
On Monday 15 December 2014 11:16:31 Ray Jui wrote:
On 12/12/2014 9:21 AM, Arnd Bergmann wrote:
On Friday 12 December 2014 09:08:48 Ray Jui wrote:
One way to solve this would be by turning the driver into a library
the same way as the pcie-dw driver, and have separate front-ends
for it for platform_device and bcma_device.

I'm fine with this solution, i.e., to introduce a common pcie-iproc core
driver (just like pcie-designware) and have different front-ends
depending on the device/bus type. If we end up deciding to go with this
solution, I need to discuss with Hauke to come up with a plan to


But before we choose to go with that route, may I ask, what is the
purpose of tying a PCIe host driver to BCMA? What benefit does BCMA give
us? If we have a generic platform based PCIe driver that can work on all
iProc SoCs + BCM4708 and BCM5301X with all HW specific configurations
taken care of by device tree, why do we still need to use BCMA?

I thought all a BCMA device here does is to auto-instantiate based on
some register readings?

Basically, DT is a hack that we only need for nondiscoverable buses.
As BCMA is (mostly) discoverable, we should use that, just like we do
for things like PCI and USB. There are clearly some limitations to
BCMA as well, e.g. on bcm4708 we don't have proper IRQ numbers in
the device list and we need to work around that using DT, but overall
it still seems to have more upsides than downsides to use it.

It's also good to point other SoC makers to Broadcom as a good example
for how to do things they claim are impossible to do.


Okay. Fair enough. Let's go with your proposal to create a generic driver pcie-iproc to be used by both bcma and platform bus. I'll initiate another email thread with you, Hauke, Scott, and me. We can discuss how to collaborate on that email thread.

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