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

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Date:	Mon, 15 Dec 2014 11:16:31 -0800
From:	Ray Jui <rjui@...adcom.com>
To:	Arnd Bergmann <arnd@...db.de>
CC:	Bjorn Helgaas <bhelgaas@...gle.com>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	"Ian Campbell" <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Grant Likely <grant.likely@...aro.org>,
	Christian Daudt <bcm@...thebug.org>,
	Matt Porter <mporter@...aro.org>,
	Florian Fainelli <f.fainelli@...il.com>,
	Russell King <linux@....linux.org.uk>,
	Hauke Mehrtens <hauke@...ke-m.de>,
	Lucas Stach <l.stach@...gutronix.de>,
	Scott Branden <sbranden@...adcom.com>,
	<linux-pci@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>,
	<bcm-kernel-feedback-list@...adcom.com>,
	<devicetree@...r.kernel.org>
Subject: Re: [PATCH v2 2/4] PCI: iproc: Add Broadcom iProc PCIe driver



On 12/12/2014 9:21 AM, Arnd Bergmann wrote:
> On Friday 12 December 2014 09:08:48 Ray Jui wrote:
>>
>> On 12/12/2014 4:29 AM, Arnd Bergmann wrote:
>> Doesn't Hauke's driver depends on BCMA? In that case, how does it work
>> on the SoCs that do not have the IP block to support BCMA?
>
> I hadn't realized that there are some SoCs that are not BCMA based.
> As the host controller implementation is closely related, we will
> have to come up with some solution.
>
I agree with you that we should have a common PCIe host driver which 
supports all iProc SoCs, BCM4708, BCM5301X, and some other similar SoCs.

> 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 
collaborate.

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?
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