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

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Message-ID: <CAHQ1cqEGABcH3EG9yGo7Ns2fPR1s_u1YPtFoKRjUh50=aa=J2Q@mail.gmail.com>
Date:   Tue, 27 Nov 2018 13:14:54 -0800
From:   Andrey Smirnov <andrew.smirnov@...il.com>
To:     Leonard Crestez <leonard.crestez@....com>,
        Lucas Stach <l.stach@...gutronix.de>
Cc:     Richard Zhu <hongxing.zhu@....com>, linux-imx@....com,
        Chris Healy <cphealy@...il.com>,
        Dong Aisheng <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
Subject: Re: [PATCH 3/3] PCI: imx: Add support for i.MX8MQ

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:
> > 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.
>

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)

Thanks,
Andrey Smirnov