linux-kernel - Re: [PATCH v2 2/3] dt-bindings: PCI: dra7xx: Add properties to enable x2 lane in dra7

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Date:   Fri, 22 Dec 2017 11:33:01 +0530
From:   Kishon Vijay Abraham I <kishon@...com>
To:     Rob Herring <robh@...nel.org>
CC:     Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Mark Rutland <mark.rutland@....com>,
        <linux-omap@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-pci@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <nsekhar@...com>
Subject: Re: [PATCH v2 2/3] dt-bindings: PCI: dra7xx: Add properties to enable
 x2 lane in dra7

Hi Rob,

On Thursday 21 December 2017 12:27 AM, Rob Herring wrote:
> On Tue, Dec 19, 2017 at 02:28:22PM +0530, Kishon Vijay Abraham I wrote:
>> Add syscon properties required for configuring PCIe in x2 lane mode.
>>
>> Signed-off-by: Kishon Vijay Abraham I <kishon@...com>
>> Signed-off-by: Sekhar Nori <nsekhar@...com>
>> ---
>>  Documentation/devicetree/bindings/pci/ti-pci.txt | 6 ++++++
>>  1 file changed, 6 insertions(+)
>>
>> diff --git a/Documentation/devicetree/bindings/pci/ti-pci.txt b/Documentation/devicetree/bindings/pci/ti-pci.txt
>> index 82cb875e4cec..bfbc77ac7355 100644
>> --- a/Documentation/devicetree/bindings/pci/ti-pci.txt
>> +++ b/Documentation/devicetree/bindings/pci/ti-pci.txt
>> @@ -13,6 +13,12 @@ PCIe DesignWare Controller
>>   - ti,hwmods : Name of the hwmod associated to the pcie, "pcie<X>",
>>  	       where <X> is the instance number of the pcie from the HW spec.
>>   - num-lanes as specified in ../designware-pcie.txt
>> + - ti,syscon-lane-conf : phandle/offset pair. Phandle to the system control
>> +			 module and the register offset to specify 1 lane or
>> +			 2 lane.
>> + - ti,syscon-lane-sel : phandle/offset pair. Phandle to the system control
>> +			module and the register offset to specify lane
>> +			selection.
> 
> Adding a property for every syscon register doesn't really scale and 
> doesn't work if the register layout changes.

The register layout doesn't really change between silicon revisions and for new
SoCs, the phandle and the register offset for that SoC will have to be
populated again.

Having said that, I'm not aware of any other alternative here.

Thanks
Kishon