linux-kernel - Re: [PATCH v5 1/9] PCI: mediatek: Using slot's devfn for compare to fix mtk_pcie_find

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Message-ID: <20181001143641.GB13049@red-moon>
Date:   Mon, 1 Oct 2018 15:36:41 +0100
From:   Lorenzo Pieralisi <lorenzo.pieralisi@....com>
To:     honghui.zhang@...iatek.com
Cc:     bhelgaas@...gle.com, linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org, ryder.lee@...iatek.com,
        ulf.hansson@...aro.org, marc.zyngier@....com,
        matthias.bgg@...il.com, devicetree@...r.kernel.org,
        yingjoe.chen@...iatek.com, eddie.huang@...iatek.com,
        youlin.pei@...iatek.com, yt.shen@...iatek.com,
        sean.wang@...iatek.com
Subject: Re: [PATCH v5 1/9] PCI: mediatek: Using slot's devfn for compare to
 fix mtk_pcie_find_port logic

On Fri, Sep 28, 2018 at 06:04:32PM +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 logic by using the slot's
> devfn for match if finding device connected to the subordinate bus.
> 
> Signed-off-by: Honghui Zhang <honghui.zhang@...iatek.com>
> ---
>  drivers/pci/controller/pcie-mediatek.c | 17 ++++++++++++++++-
>  1 file changed, 16 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/controller/pcie-mediatek.c b/drivers/pci/controller/pcie-mediatek.c
> index 9999dae..264e03f 100644
> --- a/drivers/pci/controller/pcie-mediatek.c
> +++ b/drivers/pci/controller/pcie-mediatek.c
> @@ -337,10 +337,25 @@ 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 = NULL;
> +
> +	/*
> +	 * Walk the bus hierarchy to get the devfn value
> +	 * of the port in the root bus.
> +	 */
> +	while (bus && bus->number) {
> +		dev = bus->self;
> +		bus = dev->bus;

If you add:

devfn = dev->devfn;

here

> +	}
> +
> +	list_for_each_entry(port, &pcie->ports, list) {
> +		/* Using slot's devfn to compare for subordinary bus. */
> +		if (dev)
> +			devfn = dev->devfn;

You can remove this ugly hunk altogether (and dev initialization
to NULL).

Lorenzo

> -	list_for_each_entry(port, &pcie->ports, list)
>  		if (port->slot == PCI_SLOT(devfn))
>  			return port;
> +	}
>  
>  	return NULL;
>  }
> -- 
> 2.6.4
>