linux-kernel - Re: [PATCHv2 0/4] Layerscape: Remove num-lanes property from PCIe nodes

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Message-ID: <20190822164815.GA12855@e121166-lin.cambridge.arm.com>
Date:   Thu, 22 Aug 2019 17:48:15 +0100
From:   Lorenzo Pieralisi <lorenzo.pieralisi@....com>
To:     "Z.q. Hou" <zhiqiang.hou@....com>
Cc:     "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "gustavo.pimentel@...opsys.com" <gustavo.pimentel@...opsys.com>,
        "jingoohan1@...il.com" <jingoohan1@...il.com>,
        "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>,
        Leo Li <leoyang.li@....com>,
        "andrew.murray@....com" <andrew.murray@....com>,
        "M.h. Lian" <minghuan.lian@....com>
Subject: Re: [PATCHv2 0/4] Layerscape: Remove num-lanes property from PCIe
 nodes

On Tue, Aug 20, 2019 at 07:28:37AM +0000, Z.q. Hou wrote:
> From: Hou Zhiqiang <Zhiqiang.Hou@....com>
> 
> On FSL Layerscape SoCs, the number of lanes assigned to PCIe
> controller is not fixed, it is determined by the selected
> SerDes protocol. The current num-lanes indicates the max lanes
> PCIe controller can support up to, instead of the lanes assigned
> to the PCIe controller. This can result in PCIe link training fail
> after hot-reset.
> 
> Hou Zhiqiang (4):
>   dt-bindings: PCI: designware: Remove the num-lanes from Required
>     properties
>   PCI: dwc: Return directly when num-lanes is not found
>   ARM: dts: ls1021a: Remove num-lanes property from PCIe nodes
>   arm64: dts: fsl: Remove num-lanes property from PCIe nodes
> 
>  Documentation/devicetree/bindings/pci/designware-pcie.txt | 1 -
>  arch/arm/boot/dts/ls1021a.dtsi                            | 2 --
>  arch/arm64/boot/dts/freescale/fsl-ls1012a.dtsi            | 1 -
>  arch/arm64/boot/dts/freescale/fsl-ls1043a.dtsi            | 3 ---
>  arch/arm64/boot/dts/freescale/fsl-ls1046a.dtsi            | 6 ------
>  arch/arm64/boot/dts/freescale/fsl-ls1088a.dtsi            | 3 ---
>  arch/arm64/boot/dts/freescale/fsl-ls208xa.dtsi            | 4 ----
>  drivers/pci/controller/dwc/pcie-designware.c              | 6 ++++--
>  8 files changed, 4 insertions(+), 22 deletions(-)

What a mess.

I am going to apply these but first if anyone can explain to
me what commit 907fce090253 was _supposed_ to to I would
be grateful, I read it multiple times but I still have not
understood it. This series does the right thing but why things
are they way they are in the mainline honestly I have no
idea, this does not make any sense in the slightest:

ret = of_property_read_u32(np, "num-lanes", &lanes);
if (ret)
	lanes = 0;

/* Set the number of lanes */
val = dw_pcie_readl_dbi(pci, PCIE_PORT_LINK_CONTROL);
val &= ~PORT_LINK_MODE_MASK;
switch (lanes) {
case 1:
	val |= PORT_LINK_MODE_1_LANES;
	break;
case 2:
	val |= PORT_LINK_MODE_2_LANES;
	break;
case 4:
	val |= PORT_LINK_MODE_4_LANES;
	break;
case 8:
	val |= PORT_LINK_MODE_8_LANES;
	break;
default:
	dev_err(pci->dev, "num-lanes %u: invalid value\n", lanes);
	return;
}

why do we need to set lanes to 0 if num-lanes is not present ? To print
an error message ?

I really do not understand this code.

Lorenzo