linux-kernel - Re: [PATCH] PCI: keystone: update to support multiple pci ports

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Date:	Fri, 05 Sep 2014 23:11:47 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	linux-arm-kernel@...ts.infradead.org
Cc:	Murali Karicheri <m-karicheri2@...com>,
	Mark Rutland <mark.rutland@....com>,
	devicetree@...r.kernel.org, Pawel Moll <pawel.moll@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
	Rob Herring <robh+dt@...nel.org>,
	Santosh Shilimkar <santosh.shilimkar@...com>,
	Kumar Gala <galak@...eaurora.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>
Subject: Re: [PATCH] PCI: keystone: update to support multiple pci ports

On Friday 05 September 2014 16:37:25 Murali Karicheri wrote:
> On 09/05/2014 03:00 PM, Arnd Bergmann wrote:
> > On Friday 05 September 2014 14:33:54 Murali Karicheri wrote:
> >>> This looks like it's a shared register of some sort that doesn't
> >>> really belong into the registers of a particular port. Could it
> >>> be that it's actually for the PHY?
> >>>
> >> This a shared device configuration register between the two ports the
> >> desciption states it is bootstrap configuration of the PCIe module as
> >> Endpoint or Root complex and Not Phy. Hope below text will help.
> >
> > Ok. Why do you want to have this user-selectable though? Can't it
> > just be set by the boot loader before starting Linux?
> 
> Arnd,
> 
> As the driver is responsible for configuring the device to support the 
> device functionality, it make sense to do this in the device driver. The 
> driver enables clock to the IP and this is an addition thing to be 
> configured so that when the device is powered up, it should function as 
> RC. The IP can be configured to work as Root Complex or Endpoint. So not 
> sure why you want to me to move this functionality to boot loader.

But the driver can only do root complex mode, and we would probably
want a completely different driver if we were to start supporting
endpoint mode.

This also implies that the firmware has to pass a different DT for
endpoint mode, so it should be responsible for setting up the hardware
to match the DT.

	Arnd
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