linux-kernel - Re: [PATCH v2 4/5] PCI: mediatek: Add new generation controller support

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Date:   Sat, 5 Aug 2017 14:16:53 +0800
From:   Ryder Lee <ryder.lee@...iatek.com>
To:     Bjorn Helgaas <helgaas@...nel.org>
CC:     Honghui Zhang <honghui.zhang@...iatek.com>, <bhelgaas@...gle.com>,
        <robh@...enl.org>, <robh+dt@...nel.org>, <matthias.bgg@...il.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-mediatek@...ts.infradead.org>, <linux-pci@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <yingjoe.chen@...iatek.com>, <eddie.huang@...iatek.com>,
        <hongkun.cao@...iatek.com>, <youlin.pei@...iatek.com>,
        <yong.wu@...iatek.com>, <yt.shen@...iatek.com>,
        <sean.wang@...iatek.com>, <xinping.qian@...iatek.com>
Subject: Re: [PATCH v2 4/5] PCI: mediatek: Add new generation controller
 support

On Sat, 2017-08-05 at 12:52 +0800, Ryder Lee wrote:
> Hi Honghui, Bjorn,
> 
> On Fri, 2017-08-04 at 08:18 -0500, Bjorn Helgaas wrote:
> > On Fri, Aug 04, 2017 at 04:39:36PM +0800, Honghui Zhang wrote:
> > > On Thu, 2017-08-03 at 17:42 -0500, Bjorn Helgaas wrote:
> > > > > +
> > > > > +static struct mtk_pcie_port *mtk_pcie_find_port(struct mtk_pcie *pcie,
> > > > > +						struct pci_bus *bus, int devfn)
> > > > > +{
> > > > > +	struct pci_dev *dev;
> > > > > +	struct pci_bus *pbus;
> > > > > +	struct mtk_pcie_port *port, *tmp;
> > > > > +
> > > > > +	list_for_each_entry_safe(port, tmp, &pcie->ports, list) {
> > > > > +		if (bus->number == 0 && port->index == PCI_SLOT(devfn)) {
> > > > > +			return port;
> > > > > +		} else if (bus->number != 0) {
> > > > > +			pbus = bus;
> > > > > +			do {
> > > > > +				dev = pbus->self;
> > > > > +				if (port->index == PCI_SLOT(dev->devfn))
> > > > > +					return port;
> > > > > +				pbus = dev->bus;
> > > > > +			} while (dev->bus->number != 0);
> > > > > +		}
> > > > > +	}
> > > > > +
> > > > > +	return NULL;
> > > > 
> > > > You should be able to use sysdata to avoid searching the list.
> > > > See drivers/pci/host/pci-aardvark.c, for example.
> > > > 
> > > 
> > > I could put the mtk_pcie * in sysdata, but still need to searching the
> > > list to get the mtk_pcie_port *, how about:
> > > 
> > > 	list_for_each_entry_safe(port, tmp, &pcie->ports, list) {
> > > 		if (port->index == PCI_SLOT(devfn))
> > > 			return port;
> > > 	}
> > 
> > No.  Other drivers don't need to search the list.  Please take a look
> > at them and see how they solve this problem.  I don't think your
> > hardware is fundamentally different in a way that means you need to
> > search when the others don't.
> > 
> 
> I'm not directly involved in this generation, but I guess the main reason why Honghui need to do that is just because this hardware access configuration space via per-port registers, not just for the guard.  
> Currently, We had a host bridge with two ports (two subnodes in binding text), thus he tried to tells them apart so that he can get the correct registers.
> 
> Some platforms don't need to do that since they just have a single port (no more subnodes), the others might have specific/shared registers to access configuration space. (e.g. Tegra, MTK legacy IP block).
> Or, he can split them into two independent nodes, but it will break common probing flow by doing so. (I'd prefer to use subnodes.)
> 
> Ryder
> 

Sorry for the typesetting in previous mail and noise again,

I've took a look at pci-rcar-gen2.c, this is a similar case I can found
for Honghui's case. It gathers two ports reg regions into one, and uses
the "slot id" to calculate the cfg base of each port.

Perhaps this is a example for those who need to use subnodes and use
port registers for cfg operation. Not sure whether it's worthwhile doing
that since we need to changes ports/host structures.

Ryder.