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

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Message-ID: <VI1PR04MB5533595EE55A724C7E69F297EED10@VI1PR04MB5533.eurprd04.prod.outlook.com>
Date:   Wed, 28 Nov 2018 10:55:42 +0000
From:   Leonard Crestez <leonard.crestez@....com>
To:     Andrey Smirnov <andrew.smirnov@...il.com>,
        Lucas Stach <l.stach@...gutronix.de>,
        Rob Herring <robh+dt@...nel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>
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>,
        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 11:15 PM, Andrey Smirnov wrote:
> On Tue, Nov 27, 2018 at 2:46 AM Leonard Crestez <leonard.crestez@....com> wrote:
>> On 11/27/18 12:06 PM, Lucas Stach wrote:
>>> 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.
>>
> 
> Playing devil's advocate for a bit:
> 
> More specifically, currently the following per-controller bits need to
> be configured:
> 
> - Location of the "device type" field within GPR12
> - GPR register to use to control PCIn_CLKREQ_B_OVERRIDE_EN and
> PCIn_CLKREQ_B_OVERRIDE_EN (GPR14 vs GPR16)
> - Now that Philip spoke against PCIE_CTRL_APPS_CLK_REQ being exposed
> via reset controller driver, we need to know which SRC register to use
> to control that bit (SRC_PCIEPHY_RCR vs. SRC_PCIE2_RCR)

I looked a bit through bindings and there some instances of syscon-$BLH 
properties which include detailed offsets or bitmasks for $BLAH relative 
to the target syscon node.

If you're going the route of adding properties points to IOMUXC/SRC bits 
it would sense to ensure that they're also usable on other SOCs, 
otherwise you're just making 8mq more complicated. But that's hard.

But I think it's easier to deal with such SOC-specific details behind a 
compat string. Maybe the DT list has some opinion on this?

I wonder if of_alias_get_id would be a reasonable way to distinguish 
between pcie0 and pcie1 instead of adding an ctrl-id property?

--
Regards,
Leonard