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

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Message-ID: <CAHQ1cqE0cUUsT99A5ZM6XkNd7E5+17qjZRkCdCERSp2-nWsf=Q@mail.gmail.com>
Date:   Tue, 27 Nov 2018 13:03:56 -0800
From:   Andrey Smirnov <andrew.smirnov@...il.com>
To:     Leonard Crestez <leonard.crestez@....com>
Cc:     Lucas Stach <l.stach@...gutronix.de>,
        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,
        kishon@...com, lorenzo.pieralisi@....com
Subject: Re: [PATCH 3/3] PCI: imx: Add support for i.MX8MQ

On Tue, Nov 27, 2018 at 2:16 AM Leonard Crestez <leonard.crestez@....com> wrote:
>
> 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.
>

Yeah, I am aware, I wasn't really trying to make it possible to
configure IP block to be a EP, that is just an unavoidable consequence
of the approach taken.

> 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.

Hmm, given how the mask/value have to be different for each
controller, the only way to hardcode it  that I can think of would be
to change the property pass a bit offset instead of mask/value pair.
Is that what you are suggesting?

Thanks,
Andrey Smirnov