linux-kernel - Re: [RFC PATCH v2 2/3] PCI: hisi: Make the HiSilicon PCIe host controller ECAM compliant

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Date:	Mon, 08 Feb 2016 17:29:40 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Gabriele Paoloni <gabriele.paoloni@...wei.com>
Cc:	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"Guohanjun (Hanjun Guo)" <guohanjun@...wei.com>,
	"Wangzhou (B)" <wangzhou1@...ilicon.com>,
	"liudongdong (C)" <liudongdong3@...wei.com>,
	Linuxarm <linuxarm@...wei.com>, qiujiang <qiujiang@...wei.com>,
	"bhelgaas@...gle.com" <bhelgaas@...gle.com>,
	"Lorenzo.Pieralisi@....com" <Lorenzo.Pieralisi@....com>,
	"tn@...ihalf.com" <tn@...ihalf.com>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"xuwei (O)" <xuwei5@...ilicon.com>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	"jcm@...hat.com" <jcm@...hat.com>,
	zhangjukuo <zhangjukuo@...wei.com>,
	"Liguozhu (Kenneth)" <liguozhu@...ilicon.com>
Subject: Re: [RFC PATCH v2 2/3] PCI: hisi: Make the HiSilicon PCIe host controller ECAM compliant

On Monday 08 February 2016 15:55:35 Gabriele Paoloni wrote:
> > Doesn't this break backwards compatibility?
> 
> Well Hip05/Hip06 SoCs are used into evaluation boards
> For the Estuary project.
> 
> https://github.com/hisilicon/estuary
> 
> As this new driver gets upstream we'll merge this new driver into estuary
> and release a new version of the firmware to support it.

So what happens to folks running the old firmware then?

> > I think you need to use a new compatible string in the firmware
> > if you change the register layout, and then change the driver
> > to support both the old and the new layout.
> 
> You are right, for some reason in this patchset I missed the Documentation
> update that I posted in the previous one, i.e.:
> 
> --- a/Documentation/devicetree/bindings/pci/hisilicon-pcie.txt
> +++ b/Documentation/devicetree/bindings/pci/hisilicon-pcie.txt
> @@ -23,8 +23,8 @@ Optional properties:
>  Hip05 Example (note that Hip06 is the same except compatible):
>         pcie@...0080000 {
>                 compatible = "hisilicon,hip05-pcie", "snps,dw-pcie";
> -               reg = <0 0xb0080000 0 0x10000>, <0x220 0x00000000 0 0x2000>;
> -               reg-names = "rc_dbi", "config";
> +               reg = <0 0xb0080000 0 0x10000>, <0x220 0x00100000 0 0x0f00000>;
> +               reg-names = "rc_dbi", "ecam-cfg";
> 

That is not the compatible string, it's an undocumented register set.
You can either define the a new compatible string that gives the "config"
registers a new meaning, or you change the binding to allow two either
a "config" or an "ecam-cfg" register set, and let the driver handle both.

	Arnd