linux-kernel - Re: [PATCH v15 04/13] PCI: kirin: Add support for bridge slot DT schema

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Date:   Thu, 4 Nov 2021 17:27:46 +0000
From:   Mauro Carvalho Chehab <mchehab+huawei@...nel.org>
To:     Rob Herring <robh@...nel.org>
Cc:     Bjorn Helgaas <helgaas@...nel.org>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Linuxarm <linuxarm@...wei.com>, mauro.chehab@...wei.com,
        Krzysztof Wilczyński <kw@...ux.com>,
        Binghui Wang <wangbinghui@...ilicon.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Xiaowei Song <songxiaowei@...ilicon.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        PCI <linux-pci@...r.kernel.org>,
        Kishon Vijay Abraham I <kishon@...com>
Subject: Re: [PATCH v15 04/13] PCI: kirin: Add support for bridge slot DT
 schema

Em Thu, 4 Nov 2021 10:36:52 -0500
Rob Herring <robh@...nel.org> escreveu:

> On Tue, Nov 2, 2021 at 12:44 PM Mauro Carvalho Chehab
> <mchehab+huawei@...nel.org> wrote:
> >
> > Hi Bjorn,
> >
> > Em Tue, 2 Nov 2021 11:06:12 -0500
> > Bjorn Helgaas <helgaas@...nel.org> escreveu:
> >  
> > > > +
> > > > +   /* Per-slot clkreq */
> > > > +   int             n_gpio_clkreq;
> > > > +   int             gpio_id_clkreq[MAX_PCI_SLOTS];
> > > > +   const char      *clkreq_names[MAX_PCI_SLOTS];  
> > >
> > > I think there's been previous discussion about this, but I didn't
> > > follow it, so I'm just double-checking that this is what we want here.
> > >
> > > IIUC, this (MAX_PCI_SLOTS, "hisilicon,clken-gpios") applies to an
> > > external PEX 8606 bridge, which seems a little strange to be
> > > hard-coded into the kirin driver this way.
> > >
> > > I see that "hisilicon,clken-gpios" is optional, but what if some
> > > platform connects all 6 lanes?  What if there's a different bridge
> > > altogether?  
> 
> Keep in mind this is HiKey. There's never been a 2nd board upstream
> for the SoCs, the boards have a short lifespan in terms of both
> support and availability. And yet Hikey manages to do multiple
> complicated things on the board design. I have a hard time caring...
> 
> > >
> > > I'll assume this is actually the way we want thing unless I hear
> > > otherwise.  
> >
> > Yes, there was past discussions about that with Rob, with regards
> > to how the DT would represent it, which got reflected at the code.  
> 
> At first I thought these were CLKREQ connections which absolutely
> should be per port/bridge like PERST, but they are not. They are
> simply enables for the refclk's and pretty specific to HiKey.
> 
> > At the end, it was decided to just add a single property inside PCIe:
> >
> >
> >                 pcie@...00000 {
> >                         compatible = "hisilicon,kirin970-pcie";
> > ...
> >                         hisilicon,clken-gpios = <&gpio27 3 0>, <&gpio17 0 0>,
> >                                                 <&gpio20 6 0>;
> >
> > I don't think this is a problem, as, if some day another bridge would
> > need a larger number of slots, it is just a matter of changing the
> > number at the MAX_PCI_SLOTS, as this controls only the size of the array
> > (and the check for array overflow when parsing the properties).  
> 
> It is a problem that your host bridge driver has hardcoded board
> specifics. That's not the first time you've heard that from me. But
> given the board-to-soc ratio of Hikey is 1:1, I don't care that much.

Ok, understood. Yeah, it sounds unlikely that we would get more boards
for Kirin 960/970 with PCI support, as this SoC is used for mobile phones,
where neither USB nor PCI bridges are needed. 

So, AFAIKT, the only the only publicly-available boards that will be
using this driver are HiKey 960 and HiKey 970.

Regards,
Mauro