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

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Date:   Tue, 27 Nov 2018 10:46:44 +0000
From:   Leonard Crestez <leonard.crestez@....com>
To:     Lucas Stach <l.stach@...gutronix.de>,
        Andrey Smirnov <andrew.smirnov@...il.com>
CC:     Richard Zhu <hongxing.zhu@....com>,
        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>
Subject: Re: [PATCH 3/3] PCI: imx: Add support for i.MX8MQ

On 11/27/18 12:06 PM, Lucas Stach wrote:
> Hi Andrey,
> 
> Am Montag, den 26.11.2018, 10:24 -0800 schrieb Andrey Smirnov:
>> 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:
>>>> @@ -921,7 +1004,28 @@ static int imx6_pcie_probe(struct platform_device *pdev)
>>>> -     case IMX7D:
>>>> +     case IMX8MQ:
>>>> +             if (of_property_read_u32(node, "fsl,iomux-gpr1x",
>>>> +                                      &imx6_pcie->gpr1x)) {
>>>> +                     dev_err(dev, "Failed to get GPR1x address\n");
>>>> +                     return -EINVAL;
>>>> +             }
>>>
>>> This is for distinguishing multiple controllers on the SOC but other
>>> registers and bits might differ. Isn't it preferable to have a property
>>> for controller id instead of adding many registers to DT?
>>
>> I liked encoding necessary info in DT directly slightly better than
>> encoding abstract ID and then decoding it further in the driver code.
>> OTOH, I am not really attached to that path. Lucas, can you comment on
>> this please?
> 
> Yes, after rereading the patch with this in mind I agree that having
> the GPR offset on DT directly is IMO the better approach than an
> abstract ID.

But it's not a single offset, for example the device_type (EP/RC) has 
bits for the two controllers side-by-side in GPR12.

Adding a "ctrl-id" property would fully describe the hardware from the 
start. If we add per-register information instead then when other 
registers are used we'll get DT compatibility headaches.

It's worth noting that 8qm/8qxp also have multiple controllers with a 
different set of bits placed differently in iomuxc.