linux-kernel - Re: [PATCH 3/3] PCI: imx: Add support for i.MX8MQ

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Date:   Tue, 27 Nov 2018 10:16:10 +0000
From:   Leonard Crestez <leonard.crestez@....com>
To:     Andrey Smirnov <andrew.smirnov@...il.com>,
        Lucas Stach <l.stach@...gutronix.de>,
        Richard Zhu <hongxing.zhu@....com>
CC:     dl-linux-imx <linux-imx@....com>, Chris Healy <cphealy@...il.com>,
        Aisheng DONG <aisheng.dong@....com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Rob Herring <robh+dt@...nel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        Fabio Estevam <fabio.estevam@....com>,
        Mark Rutland <mark.rutland@....com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        Kishon Vijay Abraham I <kishon@...com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>
Subject: Re: [PATCH 3/3] PCI: imx: Add support for i.MX8MQ

On 11/26/18 8:24 PM, Andrey Smirnov wrote:
> On Tue, Nov 20, 2018 at 2:49 AM Leonard Crestez <leonard.crestez@....com> wrote:
>> On Sat, 2018-11-17 at 10:12 -0800, Andrey Smirnov wrote:

>>> +             if (of_property_read_u32_array(
>>> +                         node, "fsl,gpr12-device-type",
>>> +                         imx6_pcie->device_type,
>>> +                         ARRAY_SIZE(imx6_pcie->device_type))) {
>>> +                     dev_err(dev, "Failed to get device type
>>> mask/value\n");
>>> +                     return -EINVAL;
>>> +             }
>>
>> The device type can be set on multiple SOCs, why are you adding a
>> mandatory property only for 8m?
> 
> My thinking was that other SoCs don't really have two controllers, so
> they don't really need to have that property, but, more importantly,
> not forcing them to have this property should preserve backwards
> compatibility with old DTBs.

The "device_type" registers determine Root Complex versus End Point 
mode. This is not yet supported on imx in upstream but it can be done on 
many soc versions.

Looking at other pcie controllers (and dwc core) this is normally done 
with a different compatible string with an "-ep" suffix. It feels wrong 
to expose bitmasks and values directly in DT instead.

For this patch you should probably just hardcode RC mode.