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[PATCH v2 0/7] Add MDIO bus multiplexer support for iProc SoCs

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  [PATCH v2 0/7] Add MDIO bus multiplexer support for iProc SoCs Pramod Kumar <pramod.kumar@broadcom.com> - 2016-05-31 15:40 +0200
    [PATCH v2 5/7] net:mdio-mux: Add MDIO mux driver for iProc SoCs Pramod Kumar <pramod.kumar@broadcom.com> - 2016-05-31 15:40 +0200
      Re: [PATCH v2 5/7] net:mdio-mux: Add MDIO mux driver for iProc SoCs David Miller <davem@davemloft.net> - 2016-06-02 01:20 +0200
        RE: [PATCH v2 5/7] net:mdio-mux: Add MDIO mux driver for iProc SoCs Pramod Kumar <pramod.kumar@broadcom.com> - 2016-06-03 15:50 +0200
    [PATCH v2 2/7] DT: phy.txt: Add mdio-integrated-mux property Pramod Kumar <pramod.kumar@broadcom.com> - 2016-05-31 15:40 +0200
      Re: [PATCH v2 2/7] DT: phy.txt: Add mdio-integrated-mux property Rob Herring <robh@kernel.org> - 2016-06-03 01:30 +0200
        Re: [PATCH v2 2/7] DT: phy.txt: Add mdio-integrated-mux property Andrew Lunn <andrew@lunn.ch> - 2016-06-03 02:50 +0200

#1410318 — [PATCH v2 0/7] Add MDIO bus multiplexer support for iProc SoCs

Broadcom iProc based SoCs use a MDIO bus multiplexer where child buses
could be internal as well external to SoCs. These buses could supports
MDIO transaction compatible to C-22/C-45.

Broadcom MDIO bus mulitplexer is an integrated multiplexer where child bus
selection and mdio transaction logic lies inside multiplexer itself.
To accommodate this multiplexer in existing mux framework below changes
were required-

1. Passed MDIO parent bus via mdio_mux_init to MDIO mux framework.

2. Defined one new boolean property named "mdio-integrated-mux". Integrated
   bus Multiplexer node defines this so when parent bus is registered
   by calling "of_mdiobus_register", this api will not scan for child
   nodes. Child node of integrated multiplexer will be muxed nodes not
   PHYs one hence should not be scanned.

This patch set includes MDIO bus multiplexer driver along with above
framework changes. It includes one external bus node having Ethernet PHY
attached and two internal bus node holding PCIe PHYs.

This patch series is based on v4.6.0-rc1 and is available from github-
repo: https://github.com/Broadcom/arm64-linux.git
branch:mdio-mux-v2

Changes from v1:
- stop using "brcm,is_c45" from bus node as suggested by Andrew. MDIO
PHY driver will logically OR MII_ADDR_C45 into the address when issues
any C45 MDIO read/write transaction.

Pramod Kumar (7):
  mdio:mux: Enhanced MDIO mux framework for integrated multiplexers
  DT: phy.txt: Add mdio-integrated-mux property
  binding: mdio-mux: Add DT binding doc for Broadcom MDIO bus mutiplexer
  DT:mdio-mux: Add mdio multiplexer driver node
  net:mdio-mux: Add MDIO mux driver for iProc SoCs
  Binding:PHY: Binding doc for NS2 PCIe PHYs.
  phy: Add Northstar2 PCI Phy support

 .../bindings/net/brcm,mdio-mux-iproc.txt           |  60 +++++
 Documentation/devicetree/bindings/net/mdio-mux.txt |   9 +-
 .../bindings/phy/brcm,mdio-mux-bus-pci.txt         |  27 +++
 arch/arm64/boot/dts/broadcom/ns2-svk.dts           |  12 +
 arch/arm64/boot/dts/broadcom/ns2.dtsi              |  32 +++
 drivers/net/phy/Kconfig                            |  11 +
 drivers/net/phy/Makefile                           |   1 +
 drivers/net/phy/mdio-mux-bcm-iproc.c               | 243 +++++++++++++++++++++
 drivers/net/phy/mdio-mux-gpio.c                    |   2 +-
 drivers/net/phy/mdio-mux-mmioreg.c                 |   2 +-
 drivers/net/phy/mdio-mux.c                         |  28 ++-
 drivers/of/of_mdio.c                               |   3 +
 drivers/phy/Kconfig                                |   8 +
 drivers/phy/Makefile                               |   1 +
 drivers/phy/phy-bcm-ns2-pcie.c                     | 115 ++++++++++
 include/linux/mdio-mux.h                           |   4 +-
 16 files changed, 544 insertions(+), 14 deletions(-)
 create mode 100644 Documentation/devicetree/bindings/net/brcm,mdio-mux-iproc.txt
 create mode 100644 Documentation/devicetree/bindings/phy/brcm,mdio-mux-bus-pci.txt
 create mode 100644 drivers/net/phy/mdio-mux-bcm-iproc.c
 create mode 100644 drivers/phy/phy-bcm-ns2-pcie.c

-- 
1.9.1

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#1410322 — [PATCH v2 5/7] net:mdio-mux: Add MDIO mux driver for iProc SoCs

iProc based SoCs supports the integrated mdio multiplexer which
has the bus selection as well as mdio transaction generation logic
inside.

This mutiplexer has child buses for PCIe, SATA, USB and ETH. These
buses could be internal or external to SOC where PHYs are attached.
These buses could use C-45 or C-22 mdio transaction.

Signed-off-by: Pramod Kumar <pramod.kumar@broadcom.com>
---
 drivers/net/phy/Kconfig              |  11 ++
 drivers/net/phy/Makefile             |   1 +
 drivers/net/phy/mdio-mux-bcm-iproc.c | 243 +++++++++++++++++++++++++++++++++++
 3 files changed, 255 insertions(+)
 create mode 100644 drivers/net/phy/mdio-mux-bcm-iproc.c

diff --git a/drivers/net/phy/Kconfig b/drivers/net/phy/Kconfig
index 6dad9a9..38faecf 100644
--- a/drivers/net/phy/Kconfig
+++ b/drivers/net/phy/Kconfig
@@ -254,6 +254,17 @@ config MDIO_BUS_MUX_MMIOREG
 
 	  Currently, only 8-bit registers are supported.
 
+config MDIO_BUS_MUX_BCM_IPROC
+	tristate "Support for iProc based MDIO bus multiplexers"
+	depends on OF && OF_MDIO && (ARCH_BCM_IPROC || COMPILE_TEST)
+	select MDIO_BUS_MUX
+	default ARCH_BCM_IPROC
+	help
+	  This module provides a driver for MDIO bus multiplexers found in
+	  iProc based Broadcom SoCs. This mulitplexer connects one of several
+	  child MDIO bus to a parent bus. Buses could be interal as well as
+	  external and selection logic lies inside the same multiplexer.
+
 config MDIO_BCM_UNIMAC
 	tristate "Broadcom UniMAC MDIO bus controller"
 	depends on HAS_IOMEM
diff --git a/drivers/net/phy/Makefile b/drivers/net/phy/Makefile
index fcdbb92..f5951d5a 100644
--- a/drivers/net/phy/Makefile
+++ b/drivers/net/phy/Makefile
@@ -39,6 +39,7 @@ obj-$(CONFIG_AMD_PHY)		+= amd.o
 obj-$(CONFIG_MDIO_BUS_MUX)	+= mdio-mux.o
 obj-$(CONFIG_MDIO_BUS_MUX_GPIO)	+= mdio-mux-gpio.o
 obj-$(CONFIG_MDIO_BUS_MUX_MMIOREG) += mdio-mux-mmioreg.o
+obj-$(CONFIG_MDIO_BUS_MUX_BCM_IPROC)	+= mdio-mux-bcm-iproc.o
 obj-$(CONFIG_MDIO_SUN4I)	+= mdio-sun4i.o
 obj-$(CONFIG_MDIO_MOXART)	+= mdio-moxart.o
 obj-$(CONFIG_MDIO_BCM_UNIMAC)	+= mdio-bcm-unimac.o
diff --git a/drivers/net/phy/mdio-mux-bcm-iproc.c b/drivers/net/phy/mdio-mux-bcm-iproc.c
new file mode 100644
index 0000000..f047be6
--- /dev/null
+++ b/drivers/net/phy/mdio-mux-bcm-iproc.c
@@ -0,0 +1,243 @@
+/*
+ * Copyright 2016 Broadcom
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License, version 2, as
+ * published by the Free Software Foundation (the "GPL").
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License version 2 (GPLv2) for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * version 2 (GPLv2) along with this source code.
+ */
+
+#include <linux/platform_device.h>
+#include <linux/device.h>
+#include <linux/of_mdio.h>
+#include <linux/module.h>
+#include <linux/phy.h>
+#include <linux/mdio-mux.h>
+#include <linux/delay.h>
+
+#define MDIO_PARAM_OFFSET		0x00
+#define MDIO_PARAM_MIIM_CYCLE		29
+#define MDIO_PARAM_INTERNAL_SEL		25
+#define MDIO_PARAM_BUS_ID		22
+#define MDIO_PARAM_C45_SEL		21
+#define MDIO_PARAM_PHY_ID		16
+#define MDIO_PARAM_PHY_DATA		0
+
+#define MDIO_READ_OFFSET		0x04
+#define MDIO_READ_DATA_MASK		0xffff
+#define MDIO_ADDR_OFFSET		0x08
+
+#define MDIO_CTRL_OFFSET		0x0C
+#define MDIO_CTRL_WRITE_OP		0x1
+#define MDIO_CTRL_READ_OP		0x2
+
+#define MDIO_STAT_OFFSET		0x10
+#define MDIO_STAT_DONE			1
+
+#define BUS_MAX_ADDR			32
+#define EXT_BUS_START_ADDR		16
+
+struct iproc_mdiomux_desc {
+	void *mux_handle;
+	void __iomem *base;
+	struct device *dev;
+	struct mii_bus *mii_bus;
+};
+
+static int iproc_mdio_wait_for_idle(void __iomem *base, bool result)
+{
+	u32 val;
+	unsigned int timeout = 1000; /* loop for 1s */
+
+	do {
+		val = readl(base + MDIO_STAT_OFFSET);
+		if ((val & MDIO_STAT_DONE) == result)
+			return 0;
+
+		usleep_range(1000, 2000);
+	} while (timeout--);
+
+	return -ETIMEDOUT;
+}
+
+/* start_miim_ops- Program and start MDIO transaction over mdio bus.
+ * @base: Base address
+ * @phyid: phyid of the selected bus.
+ * @reg: register offset to be read/written.
+ * @val :0 if read op else value to be written in @reg;
+ * @op: Operation that need to be carried out.
+ *      MDIO_CTRL_READ_OP: Read transaction.
+ *      MDIO_CTRL_WRITE_OP: Write transaction.
+ *
+ * Return value: Successful Read operation returns read reg values and write
+ *      operation returns 0. Failure operation returns negative error code.
+ */
+static int start_miim_ops(void __iomem *base,
+			  u16 phyid, u32 reg, u16 val, u32 op)
+{
+	int ret;
+	u32 param;
+
+	writel(0, base + MDIO_CTRL_OFFSET);
+	ret = iproc_mdio_wait_for_idle(base, 0);
+	if (ret)
+		goto err;
+
+	param = readl(base + MDIO_PARAM_OFFSET);
+	param |= phyid << MDIO_PARAM_PHY_ID;
+	param |= val << MDIO_PARAM_PHY_DATA;
+	if (reg & MII_ADDR_C45)
+		param |= (1 << MDIO_PARAM_C45_SEL);
+
+	writel(param, base + MDIO_PARAM_OFFSET);
+
+	writel(reg, base + MDIO_ADDR_OFFSET);
+
+	writel(op, base + MDIO_CTRL_OFFSET);
+
+	ret = iproc_mdio_wait_for_idle(base, 1);
+	if (ret)
+		goto err;
+
+	if (op == MDIO_CTRL_READ_OP)
+		ret = readl(base + MDIO_READ_OFFSET) & MDIO_READ_DATA_MASK;
+err:
+	return ret;
+}
+
+static int iproc_mdiomux_read(struct mii_bus *bus, int phyid, int reg)
+{
+	int ret;
+	struct iproc_mdiomux_desc *md = bus->priv;
+
+	ret = start_miim_ops(md->base, phyid, reg, 0, MDIO_CTRL_READ_OP);
+	if (ret < 0)
+		dev_err(&bus->dev, "mdiomux read operation failed!!!");
+
+	return ret;
+}
+
+static int iproc_mdiomux_write(struct mii_bus *bus,
+			       int phyid, int reg, u16 val)
+{
+	int ret;
+	struct iproc_mdiomux_desc *md = bus->priv;
+
+	/* Write val at reg offset */
+	ret = start_miim_ops(md->base, phyid, reg, val, MDIO_CTRL_WRITE_OP);
+	if (ret < 0)
+		dev_err(&bus->dev, "mdiomux write operation failed!!!");
+
+	return ret;
+}
+
+static int mdio_mux_iproc_switch_fn(int current_child, int desired_child,
+				    void *data)
+{
+	struct iproc_mdiomux_desc *md = data;
+	u32 param, bus_id;
+	bool bus_dir;
+
+	/* select bus and its properties */
+	bus_dir = (desired_child < EXT_BUS_START_ADDR);
+	bus_id = bus_dir ? desired_child : (desired_child - EXT_BUS_START_ADDR);
+
+	param = (bus_dir ? 1 : 0) << MDIO_PARAM_INTERNAL_SEL;
+	param |= (bus_id << MDIO_PARAM_BUS_ID);
+
+	writel(param, md->base + MDIO_PARAM_OFFSET);
+	return 0;
+}
+
+static int mdio_mux_iproc_probe(struct platform_device *pdev)
+{
+	struct iproc_mdiomux_desc *md;
+	struct mii_bus *bus;
+	struct resource *res;
+	int rc;
+
+	md = devm_kzalloc(&pdev->dev, sizeof(*md), GFP_KERNEL);
+	if (!md)
+		return -ENOMEM;
+	md->dev = &pdev->dev;
+
+	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
+	md->base = devm_ioremap_resource(&pdev->dev, res);
+	if (IS_ERR(md->base)) {
+		dev_err(&pdev->dev, "failed to ioremap register\n");
+		return PTR_ERR(md->base);
+	}
+
+	md->mii_bus = mdiobus_alloc();
+	if (!md->mii_bus) {
+		dev_err(&pdev->dev, "mdiomux bus alloc failed\n");
+		return -ENOMEM;
+	}
+
+	bus = md->mii_bus;
+	bus->priv = md;
+	bus->name = "iProc MDIO mux bus";
+	snprintf(bus->id, MII_BUS_ID_SIZE, "%s-%d", pdev->name, pdev->id);
+	bus->parent = &pdev->dev;
+	bus->read = iproc_mdiomux_read;
+	bus->write = iproc_mdiomux_write;
+
+	rc = of_mdiobus_register(bus, pdev->dev.of_node);
+	if (rc) {
+		dev_err(&pdev->dev, "mdiomux registration failed\n");
+		goto out;
+	}
+
+	platform_set_drvdata(pdev, md);
+
+	rc = mdio_mux_init(md->dev, mdio_mux_iproc_switch_fn,
+			   &md->mux_handle, md, md->mii_bus);
+	if (rc) {
+		dev_info(md->dev, "mdiomux initialization failed\n");
+		goto out;
+	}
+
+	dev_info(md->dev, "iProc mdiomux registered\n");
+	return 0;
+out:
+	mdiobus_free(bus);
+	return rc;
+}
+
+static int mdio_mux_iproc_remove(struct platform_device *pdev)
+{
+	struct iproc_mdiomux_desc *md = dev_get_platdata(&pdev->dev);
+
+	mdio_mux_uninit(md->mux_handle);
+	return 0;
+}
+
+static const struct of_device_id mdio_mux_iproc_match[] = {
+	{
+		.compatible = "brcm,mdio-mux-iproc",
+	},
+	{},
+};
+MODULE_DEVICE_TABLE(of, mdio_mux_iproc_match);
+
+static struct platform_driver mdiomux_iproc_driver = {
+	.driver = {
+		.name		= "mdio-mux-iproc",
+		.of_match_table = mdio_mux_iproc_match,
+	},
+	.probe		= mdio_mux_iproc_probe,
+	.remove		= mdio_mux_iproc_remove,
+};
+
+module_platform_driver(mdiomux_iproc_driver);
+
+MODULE_DESCRIPTION("iProc MDIO Mux Bus Driver");
+MODULE_AUTHOR("Pramod Kumar <pramod.kumar@broadcom.com>");
+MODULE_LICENSE("GPL v2");
-- 
1.9.1

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#1411648 — Re: [PATCH v2 5/7] net:mdio-mux: Add MDIO mux driver for iProc SoCs

From: Pramod Kumar <pramod.kumar@broadcom.com>
Date: Tue, 31 May 2016 19:06:39 +0530

> +static int iproc_mdio_wait_for_idle(void __iomem *base, bool result)
> +{
> +	u32 val;
> +	unsigned int timeout = 1000; /* loop for 1s */

Please order your local variable declarations from longest to shortest line.

> +static int start_miim_ops(void __iomem *base,
> +			  u16 phyid, u32 reg, u16 val, u32 op)
> +{
> +	int ret;
> +	u32 param;

Likewise.

> +static int iproc_mdiomux_read(struct mii_bus *bus, int phyid, int reg)
> +{
> +	int ret;
> +	struct iproc_mdiomux_desc *md = bus->priv;

Likewise.

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#1413257 — RE: [PATCH v2 5/7] net:mdio-mux: Add MDIO mux driver for iProc SoCs

Hi David,

> -----Original Message-----
> From: David Miller [mailto:davem@davemloft.net]
> Sent: 02 June 2016 04:48
> To: pramod.kumar@broadcom.com
> Cc: robh+dt@kernel.org; pawel.moll@arm.com; mark.rutland@arm.com;
> ijc+devicetree@hellion.org.uk; galak@codeaurora.org;
> catalin.marinas@arm.com; will.deacon@arm.com; kishon@ti.com;
> devicetree@vger.kernel.org; linux-arm-kernel@lists.infradead.org;
bcm-kernel-
> feedback-list@broadcom.com; linux-kernel@vger.kernel.org;
> netdev@vger.kernel.org
> Subject: Re: [PATCH v2 5/7] net:mdio-mux: Add MDIO mux driver for iProc
SoCs
>
> From: Pramod Kumar <pramod.kumar@broadcom.com>
> Date: Tue, 31 May 2016 19:06:39 +0530
>
> > +static int iproc_mdio_wait_for_idle(void __iomem *base, bool result)
> > +{
> > +	u32 val;
> > +	unsigned int timeout = 1000; /* loop for 1s */
>
> Please order your local variable declarations from longest to shortest
line.
>
> > +static int start_miim_ops(void __iomem *base,
> > +			  u16 phyid, u32 reg, u16 val, u32 op) {
> > +	int ret;
> > +	u32 param;
>
> Likewise.
>
Sure. I'll take care of this in next patch for all places.

> > +static int iproc_mdiomux_read(struct mii_bus *bus, int phyid, int
> > +reg) {
> > +	int ret;
> > +	struct iproc_mdiomux_desc *md = bus->priv;
>
> Likewise.
Sure. I'll take care of this in next patch for all places.

Regards,
Pramod

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#1410323 — [PATCH v2 2/7] DT: phy.txt: Add mdio-integrated-mux property

This property is used by integrated MDIO multiplexer
which has bus selection and mdio transaction generation logic,
integrated inside.

Signed-off-by: Pramod Kumar <pramod.kumar@broadcom.com>
---
 Documentation/devicetree/bindings/net/mdio-mux.txt | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/Documentation/devicetree/bindings/net/mdio-mux.txt b/Documentation/devicetree/bindings/net/mdio-mux.txt
index 491f5bd..b5ad83e 100644
--- a/Documentation/devicetree/bindings/net/mdio-mux.txt
+++ b/Documentation/devicetree/bindings/net/mdio-mux.txt
@@ -5,13 +5,20 @@ numbered uniquely in a device dependent manner.  The nodes for an MDIO
 bus multiplexer/switch will have one child node for each child bus.
 
 Required properties:
-- mdio-parent-bus : phandle to the parent MDIO bus.
 - #address-cells = <1>;
 - #size-cells = <0>;
 
 Optional properties:
+- mdio-parent-bus : phandle to the parent MDIO bus. Should be used
+		if parent mdio bus is not part of multiplexer.
+- mdio-integrated-mux: boolean property indicateing that the hardware
+		is an integrated multiplex supporting muxed bus selection
+		and MDIO transaction logic generation.
 - Other properties specific to the multiplexer/switch hardware.
 
+Note: one of mdio-parent-bus and mdio-integrated-mux is mandatory to
+get parent bus regsitered.
+
 Required properties for child nodes:
 - #address-cells = <1>;
 - #size-cells = <0>;
-- 
1.9.1

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#1412615 — Re: [PATCH v2 2/7] DT: phy.txt: Add mdio-integrated-mux property

On Tue, May 31, 2016 at 07:06:36PM +0530, Pramod Kumar wrote:
> This property is used by integrated MDIO multiplexer
> which has bus selection and mdio transaction generation logic,
> integrated inside.
> 
> Signed-off-by: Pramod Kumar <pramod.kumar@broadcom.com>
> ---
>  Documentation/devicetree/bindings/net/mdio-mux.txt | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/devicetree/bindings/net/mdio-mux.txt b/Documentation/devicetree/bindings/net/mdio-mux.txt
> index 491f5bd..b5ad83e 100644
> --- a/Documentation/devicetree/bindings/net/mdio-mux.txt
> +++ b/Documentation/devicetree/bindings/net/mdio-mux.txt
> @@ -5,13 +5,20 @@ numbered uniquely in a device dependent manner.  The nodes for an MDIO
>  bus multiplexer/switch will have one child node for each child bus.
>  
>  Required properties:
> -- mdio-parent-bus : phandle to the parent MDIO bus.
>  - #address-cells = <1>;
>  - #size-cells = <0>;
>  
>  Optional properties:
> +- mdio-parent-bus : phandle to the parent MDIO bus. Should be used
> +		if parent mdio bus is not part of multiplexer.

You don't appear to be using this. When would you?

> +- mdio-integrated-mux: boolean property indicateing that the hardware
> +		is an integrated multiplex supporting muxed bus selection
> +		and MDIO transaction logic generation.
>  - Other properties specific to the multiplexer/switch hardware.
>  
> +Note: one of mdio-parent-bus and mdio-integrated-mux is mandatory to
> +get parent bus regsitered.
> +
>  Required properties for child nodes:
>  - #address-cells = <1>;
>  - #size-cells = <0>;
> -- 
> 1.9.1
> 

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#1412656 — Re: [PATCH v2 2/7] DT: phy.txt: Add mdio-integrated-mux property

On Thu, Jun 02, 2016 at 06:27:03PM -0500, Rob Herring wrote:
> On Tue, May 31, 2016 at 07:06:36PM +0530, Pramod Kumar wrote:
> > This property is used by integrated MDIO multiplexer
> > which has bus selection and mdio transaction generation logic,
> > integrated inside.
> > 
> > Signed-off-by: Pramod Kumar <pramod.kumar@broadcom.com>
> > ---
> >  Documentation/devicetree/bindings/net/mdio-mux.txt | 9 ++++++++-
> >  1 file changed, 8 insertions(+), 1 deletion(-)
> > 
> > diff --git a/Documentation/devicetree/bindings/net/mdio-mux.txt b/Documentation/devicetree/bindings/net/mdio-mux.txt
> > index 491f5bd..b5ad83e 100644
> > --- a/Documentation/devicetree/bindings/net/mdio-mux.txt
> > +++ b/Documentation/devicetree/bindings/net/mdio-mux.txt
> > @@ -5,13 +5,20 @@ numbered uniquely in a device dependent manner.  The nodes for an MDIO
> >  bus multiplexer/switch will have one child node for each child bus.
> >  
> >  Required properties:
> > -- mdio-parent-bus : phandle to the parent MDIO bus.
> >  - #address-cells = <1>;
> >  - #size-cells = <0>;
> >  
> >  Optional properties:
> > +- mdio-parent-bus : phandle to the parent MDIO bus. Should be used
> > +		if parent mdio bus is not part of multiplexer.
> 
> You don't appear to be using this. When would you?

He is moving it to optional. The mdio-mux-mmio and mdio-mux-gpio do
however use it, which follow this binding.

	Andrew

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