linux-kernel - Re: [PATCH v4 1/4] PCI: mediatek: fixup mtk_pcie_find

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Date:   Wed, 26 Sep 2018 17:06:57 +0800
From:   Honghui Zhang <honghui.zhang@...iatek.com>
To:     Lorenzo Pieralisi <lorenzo.pieralisi@....com>
CC:     <marc.zyngier@....com>, <bhelgaas@...gle.com>,
        <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>,
        <ryder.lee@...iatek.com>, <ulf.hansson@...aro.org>,
        <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 v4 1/4] PCI: mediatek: fixup mtk_pcie_find_port logical

On Fri, 2018-09-21 at 17:07 +0100, Lorenzo Pieralisi wrote:
> On Mon, Sep 10, 2018 at 05:50:20PM +0800, honghui.zhang@...iatek.com wrote:
> > From: Honghui Zhang <honghui.zhang@...iatek.com>
> > 
> > The Mediatek's host controller has two slots, each with it's own control
> > registers. The host driver need to identify which slot was connected
> > in order to access the device's configuration space. There's problem
> > for current host driver to find out which slot was connected to for
> > a given EP device.
> > 
> > Assuming each slot have connect with one EP device as below:
> > 
> >                 host bridge
> >   bus 0 --> __________|_______
> >            |                  |
> >            |                  |
> >          slot 0             slot 1
> >   bus 1 -->|        bus 2 --> |
> >            |                  |
> >          EP 0               EP 1
> > 
> > During PCI enumeration, system software will scan all the PCI device
> > starting from devfn 0. So it will get the proper port for slot0 and
> > slot1 device when using PCI_SLOT(devfn) for match. But it will get
> > the wrong slot for EP1: The devfn will be start from 0 when scanning
> > EP1 behind slot1, it will get port0 since the PCI_SLOT(EP1) is match
> > for port0's slot value. So the host driver should not using EP's devfn
> > but the slot's devfn(the slot which EP was connected to) for match.
> > 
> > This patch fix the mtk_pcie_find_port's logical by using the slot's
> > devfn for match.
> > 
> > Signed-off-by: Honghui Zhang <honghui.zhang@...iatek.com>
> > Acked-by: Ryder Lee <ryder.lee@...iatek.com>
> > ---
> >  drivers/pci/controller/pcie-mediatek.c | 19 +++++++++++++++++--
> >  1 file changed, 17 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/pci/controller/pcie-mediatek.c b/drivers/pci/controller/pcie-mediatek.c
> > index 861dda6..20b9088 100644
> > --- a/drivers/pci/controller/pcie-mediatek.c
> > +++ b/drivers/pci/controller/pcie-mediatek.c
> > @@ -337,11 +337,26 @@ static struct mtk_pcie_port *mtk_pcie_find_port(struct pci_bus *bus,
> >  {
> >  	struct mtk_pcie *pcie = bus->sysdata;
> >  	struct mtk_pcie_port *port;
> > +	struct pci_dev *dev;
> > +	struct pci_bus *pbus;
> >  
> > -	list_for_each_entry(port, &pcie->ports, list)
> > -		if (port->slot == PCI_SLOT(devfn))
> > +	list_for_each_entry(port, &pcie->ports, list) {
> > +		if (!bus->number && port->slot == PCI_SLOT(devfn))
> >  			return port;
> >  
> > +		if (bus->number) {
> > +			pbus = bus;
> > +
> > +			while (pbus->number) {
> > +				dev = pbus->self;
> > +				pbus = dev->bus;
> > +			}
> > +
> > +			if (port->slot == PCI_SLOT(dev->devfn))
> > +				return port;
> > +		}
> > +	}
> 
> 	/*
> 	 * Walk the bus hierarchy to get the devfn value
> 	 * of the port in the root bus.
> 	 */
> 	while (bus && bus->number) {
> 		devfn = bus->self->devfn;
> 		bus = bus->parent;
> 	}
> 
> 	list_for_each_entry(port, &pcie->ports, list) {
> 		if (port->slot == PCI_SLOT(devfn))
> 			return port;
> 
> 	return NULL;
> 
> Would it work ? Maybe it is a little easier to parse.
> 

Thanks, this is much better.

> I think this can even be made easier by using struct device_node* as
> comparison (and store it in port->slot instead of the port number), I
> think that the pci_dev representing the port should have the right
> of_node associated with it by core code, so it is just a matter of
> finding the first pci_dev parent with an of_node set and compare it
> against port->slot (that should be converted to a struct device_node*).
> 
> This ought to be tested and written but I think that's doable.
> 

Thanks, I will do my homework and figure a way out through this
solution.
Currently port->slot is used in too much place to be removed, I guess I
need to added a new parameter in the port struct to store the of_node
for compare.
I'm not sure which way is better, anyway, let me try the new solution.

thanks.

> Lorenzo