linux-kernel - Re: [PATCH v14 04/11] PCI: kirin: Add support for bridge slot DT schema

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Date:   Tue, 24 May 2022 13:59:44 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Mauro Carvalho Chehab <mchehab@...nel.org>
Cc:     Lorenzo Pieralisi <lorenzo.pieralisi@....com>, linuxarm@...wei.com,
        mauro.chehab@...wei.com,
        Krzysztof Wilczyński <kw@...ux.com>,
        Songxiaowei <songxiaowei@...ilicon.com>,
        Binghui Wang <wangbinghui@...ilicon.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Rob Herring <robh@...nel.org>, linux-kernel@...r.kernel.org,
        linux-pci@...r.kernel.org, Kishon Vijay Abraham I <kishon@...com>
Subject: Re: [PATCH v14 04/11] PCI: kirin: Add support for bridge slot DT
 schema

[resending with updated address for Mauro]

On Tue, May 24, 2022 at 12:19:50PM -0500, Bjorn Helgaas wrote:
> On Tue, Oct 19, 2021 at 07:06:41AM +0100, Mauro Carvalho Chehab wrote:
> > On HiKey970, there's a PEX 8606 PCI bridge on its PHY with
> > 6 lanes. Only 4 lanes are connected:
> > 
> > 	lane 0 - connected to Kirin 970;
> > 	lane 4 - M.2 slot;
> > 	lane 5 - mini PCIe slot;
> > 	lane 6 - in-board Ethernet controller.
> > 
> > Each lane has its own PERST# gpio pin, and needs a clock
> > request.
> > 
> > Add support to parse a DT schema containing the above data.
> > 
> > Cc: Kishon Vijay Abraham I <kishon@...com>
> > Acked-by: Xiaowei Song <songxiaowei@...ilicon.com>
> > Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@...nel.org>
> > ---
> > 
> > See [PATCH v14 00/11] at: https://lore.kernel.org/all/cover.1634622716.git.mchehab+huawei@kernel.org/
> > 
> >  drivers/pci/controller/dwc/pcie-kirin.c | 262 +++++++++++++++++++++---
> >  1 file changed, 231 insertions(+), 31 deletions(-)
> > 
> > diff --git a/drivers/pci/controller/dwc/pcie-kirin.c b/drivers/pci/controller/dwc/pcie-kirin.c
> > index 86c13661e02d..de375795a3b8 100644
> > --- a/drivers/pci/controller/dwc/pcie-kirin.c
> > +++ b/drivers/pci/controller/dwc/pcie-kirin.c
> > @@ -52,6 +52,19 @@
> >  #define PCIE_DEBOUNCE_PARAM	0xF0F400
> >  #define PCIE_OE_BYPASS		(0x3 << 28)
> >  
> > +/*
> > + * Max number of connected PCI slots at an external PCI bridge
> > + *
> > + * This is used on HiKey 970, which has a PEX 8606 bridge with has
> > + * 4 connected lanes (lane 0 upstream, and the other tree lanes,
> > + * one connected to an in-board Ethernet adapter and the other two
> > + * connected to M.2 and mini PCI slots.
> > + *
> > + * Each slot has a different clock source and uses a separate PERST#
> > + * pin.
> > ...
> 
> > +static int kirin_pcie_add_bus(struct pci_bus *bus)
> > +{
> > +	struct dw_pcie *pci = to_dw_pcie_from_pp(bus->sysdata);
> > +	struct kirin_pcie *kirin_pcie = to_kirin_pcie(pci);
> > +	int i, ret;
> > +
> > +	if (!kirin_pcie->num_slots)
> > +		return 0;
> > +
> > +	/* Send PERST# to each slot */
> > +	for (i = 0; i < kirin_pcie->num_slots; i++) {
> > +		ret = gpio_direction_output(kirin_pcie->gpio_id_reset[i], 1);
> > +		if (ret) {
> > +			dev_err(pci->dev, "PERST# %s error: %d\n",
> > +				kirin_pcie->reset_names[i], ret);
> > +		}
> > +	}
> > +	usleep_range(PERST_2_ACCESS_MIN, PERST_2_ACCESS_MAX);
> > +
> > +	return 0;
> > +}
> > +
> > +
> >  static struct pci_ops kirin_pci_ops = {
> >  	.read = kirin_pcie_rd_own_conf,
> >  	.write = kirin_pcie_wr_own_conf,
> > +	.add_bus = kirin_pcie_add_bus,
> 
> This seems a little weird.  Can you educate me?
> 
> From [1], it looks like the topology here is:
> 
>   00:00.0 Root Port
>   01:00.0 PEX 8606 Upstream Port
>   02:01.0 PEX 8606 Downstream Port
>   02:04.0 PEX 8606 Downstream Port
>   02:05.0 PEX 8606 Downstream Port
>   02:07.0 PEX 8606 Downstream Port
>   02:09.0 PEX 8606 Downstream Port
>   06:00.0 RTL8111/8168/8411 PCI Express Gigabit Ethernet Controller 
> 
> The .add_bus() callback will be called for *every* child bus we want
> to enumerate.  So if any of those PEX 8606 Downstream Ports are
> connected to another switch, when we enumerate the secondary buses of
> that other switch, it looks like we'll send PERST# to all the slots
> again, which doesn't sound right.  Am I missing something?
> 
> Bjorn
> 
> [1] https://lore.kernel.org/all/20210129173057.30288c9d@coco.lan/