Date:   Mon, 10 Oct 2016 17:29:26 +0200
From:   Peter Rosin <peda@...ntia.se>
To:     Pantelis Antoniou <pantelis.antoniou@...sulko.com>,
        Lee Jones <lee.jones@...aro.org>
CC:     Linus Walleij <linus.walleij@...aro.org>,
        Alexandre Courbot <gnurou@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Frank Rowand <frowand.list@...il.com>,
        Wolfram Sang <wsa@...-dreams.de>,
        Richard Purdie <rpurdie@...ys.net>,
        Jacek Anaszewski <j.anaszewski@...sung.com>,
        Jean Delvare <jdelvare@...e.com>,
        Avirup Banerjee <abanerjee@...iper.net>,
        Georgi Vlaev <gvlaev@...iper.net>,
        Guenter Roeck <linux@...ck-us.net>,
        JawaharBalaji Thirumalaisamy <jawaharb@...iper.net>,
        <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-gpio@...r.kernel.org>, <linux-i2c@...r.kernel.org>,
        <linux-leds@...r.kernel.org>, <linux-hwmon@...r.kernel.org>
Subject: Re: [PATCH 03/10] i2c/muxes: Juniper I2CS RE mux

On 2016-10-07 17:21, Pantelis Antoniou wrote:
> From: Georgi Vlaev <gvlaev@...iper.net>
> 
> Add support for Juniper I2C Slave RE multiplexer driver.
> 
> This I2C multiplexer driver allows the RE to access some of
> the FPC I2C buses. It's compatible only with the FPC variant of the
> I2CS.
> 
> Signed-off-by: Georgi Vlaev <gvlaev@...iper.net>
> Signed-off-by: Guenter Roeck <groeck@...iper.net>
> [Ported from Juniper kernel]
> Signed-off-by: Pantelis Antoniou <pantelis.antoniou@...sulko.com>
> ---
>  drivers/i2c/muxes/Kconfig        |  10 +++
>  drivers/i2c/muxes/Makefile       |   1 +
>  drivers/i2c/muxes/i2c-mux-i2cs.c | 155 +++++++++++++++++++++++++++++++++++++++
>  3 files changed, 166 insertions(+)
>  create mode 100644 drivers/i2c/muxes/i2c-mux-i2cs.c
> 
> diff --git a/drivers/i2c/muxes/Kconfig b/drivers/i2c/muxes/Kconfig
> index f45a9cb..c95380d 100644
> --- a/drivers/i2c/muxes/Kconfig
> +++ b/drivers/i2c/muxes/Kconfig
> @@ -30,6 +30,16 @@ config I2C_MUX_GPIO
>  	  This driver can also be built as a module.  If so, the module
>  	  will be called i2c-mux-gpio.
>  
> +config I2C_MUX_I2CS
> +	tristate "Juniper I2C Slave MFD client RE multiplexer"
> +	depends on MFD_JUNIPER_I2CS
> +	help
> +	  Select this to enable the Juniper I2C Slave RE multiplexer driver
> +	  on the relevant Juniper platforms.
> +
> +	  This driver can also be built as a module.  If so, the module
> +	  will be called i2c-mux-i2cs.
> +
>  config I2C_MUX_PCA9541
>  	tristate "NXP PCA9541 I2C Master Selector"
>  	help
> diff --git a/drivers/i2c/muxes/Makefile b/drivers/i2c/muxes/Makefile
> index 78d8cba..45b4287 100644
> --- a/drivers/i2c/muxes/Makefile
> +++ b/drivers/i2c/muxes/Makefile
> @@ -6,6 +6,7 @@ obj-$(CONFIG_I2C_ARB_GPIO_CHALLENGE)	+= i2c-arb-gpio-challenge.o
>  obj-$(CONFIG_I2C_DEMUX_PINCTRL)		+= i2c-demux-pinctrl.o
>  
>  obj-$(CONFIG_I2C_MUX_GPIO)	+= i2c-mux-gpio.o
> +obj-$(CONFIG_I2C_MUX_I2CS)	+= i2c-mux-i2cs.o
>  obj-$(CONFIG_I2C_MUX_PCA9541)	+= i2c-mux-pca9541.o
>  obj-$(CONFIG_I2C_MUX_PCA954x)	+= i2c-mux-pca954x.o
>  obj-$(CONFIG_I2C_MUX_PINCTRL)	+= i2c-mux-pinctrl.o
> diff --git a/drivers/i2c/muxes/i2c-mux-i2cs.c b/drivers/i2c/muxes/i2c-mux-i2cs.c

Please name the file i2c-mux-jnx-i2cs.c. Or something else a bit more
specific.

> new file mode 100644
> index 0000000..c498a44
> --- /dev/null
> +++ b/drivers/i2c/muxes/i2c-mux-i2cs.c
> @@ -0,0 +1,155 @@
> +/*
> + * Juniper Networks I2CS RE mux driver
> + *
> + * Copyright (C) 2012, 2013, 2014 Juniper Networks. All rights reserved.
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License as published by
> + * the Free Software Foundation; either version 2 of the License, or
> + * (at your option) any later version.
> + *
> + * 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 for more details.
> + */
> +
> +#include <linux/init.h>

init?

> +#include <linux/device.h>
> +#include <linux/module.h>
> +#include <linux/kernel.h>
> +#include <linux/i2c.h>
> +#include <linux/i2c-mux.h>
> +#include <linux/regmap.h>

regmap?

> +#include <linux/platform_device.h>
> +#include <linux/mfd/jnx-i2cs-core.h>
> +
> +#define MISC_IO_RE_EN	0x01
> +
> +/*
> + * Read/write to mux register.
> + *   Don't use i2c_transfer()/i2c_smbus_xfer()
> + *   for this as they will try to lock adapter a second time
> + */

If this is the only concern, you should consider making this
gate mux-locked instead of parent-locked. Then you can avoid
all these unlocked games. But there are caveats, so you better
read Documentation/i2c/i2c-topology for the details before
you change.

> +static int i2cs_mux_read_byte(struct i2c_client *client,
> +				  u8 offset, u8 *val)
> +{
> +	struct i2c_msg msg[2];
> +
> +	msg[0].addr = client->addr;
> +	msg[0].flags = 0;
> +	msg[0].len = 1;
> +	msg[0].buf = &offset;
> +
> +	msg[1].addr = client->addr;
> +	msg[1].flags = I2C_M_RD;
> +	msg[1].len = 1;
> +	msg[1].buf = val;
> +
> +	return client->adapter->algo->master_xfer(client->adapter, msg, 2);

If you still want to be parent-locked, use __i2c_transfer. In
either case, consider adding code that handles the case of no
algo->master_xfer (some i2c adapters only support
algo->smbus_xfer).

> +}
> +
> +static int i2cs_mux_write_byte(struct i2c_client *client, u8 offset, u8 val)
> +{
> +	struct i2c_msg msg;
> +	char buf[2];
> +
> +	msg.addr = client->addr;
> +	msg.flags = 0;
> +	msg.len = 2;
> +	buf[0] = offset;
> +	buf[1] = val;
> +	msg.buf = buf;
> +
> +	return client->adapter->algo->master_xfer(client->adapter, &msg, 1);
> +}
> +
> +static int i2cs_mux_select(struct i2c_mux_core *muxc, u32 chan)
> +{
> +	int ret;
> +	u8 val = 0;
> +	struct i2c_client *client = i2c_mux_priv(muxc);
> +
> +	ret = i2cs_mux_read_byte(client, I2CS_MISC_IO, &val);
> +	if (ret < 0)
> +		return ret;
> +
> +	val |= MISC_IO_RE_EN;
> +	ret = i2cs_mux_write_byte(client, I2CS_MISC_IO, val);
> +

To me, it sounds as if I2CS_MISC_IO is a register with more than
one bit and that you are open to nasty races here. You probably
need to interact with the mfd parent and arrange some locking.

> +	return ret;
> +}
> +
> +static int i2cs_mux_deselect(struct i2c_mux_core *muxc, u32 chan)
> +{
> +	int ret;
> +	u8 val = 0;
> +	struct i2c_client *client = i2c_mux_priv(muxc);
> +
> +	ret = i2cs_mux_read_byte(client, I2CS_MISC_IO, &val);
> +	if (ret < 0)
> +		return ret;
> +
> +	val &= ~MISC_IO_RE_EN;
> +	ret = i2cs_mux_write_byte(client, I2CS_MISC_IO, val);
> +
> +	return 0;
> +}
> +
> +static int i2cs_mux_probe(struct platform_device *pdev)
> +{
> +	struct device *dev = &pdev->dev;
> +	struct i2c_client *client;
> +	struct i2c_mux_core *muxc;
> +	int ret;
> +
> +	if (!dev->parent)
> +		return -ENODEV;
> +
> +	client = i2c_verify_client(dev->parent);
> +	if (!client)
> +		return -ENODEV;
> +
> +	muxc = i2c_mux_alloc(client->adapter, &client->dev, 1, 0, 0,
> +				i2cs_mux_select, i2cs_mux_deselect);

You only have one child adapter, making this a gate. Please use
the I2C_MUX_GATE flag which should be available in 4.9. This also
affects the preferred devicetree, see comment on that patch.

> +	if (!muxc)
> +		return -ENOMEM;
> +	muxc->priv = client;
> +
> +	ret = i2c_mux_add_adapter(muxc, 0, 0, 0);
> +	if (ret)
> +		return ret;
> +
> +	platform_set_drvdata(pdev, muxc);
> +
> +	return 0;
> +}
> +
> +static int i2cs_mux_remove(struct platform_device *pdev)
> +{
> +	i2c_mux_del_adapters(platform_get_drvdata(pdev));
> +
> +	return 0;
> +}
> +
> +static const struct of_device_id i2cs_mux_of_match[] = {
> +	{ .compatible = "jnx,i2c-mux-i2cs", },
> +	{},
> +};
> +MODULE_DEVICE_TABLE(of, i2cs_mux_of_match);
> +
> +static struct platform_driver i2cs_mux_driver = {
> +	.driver = {
> +		.name = "i2c-mux-i2cs",
> +		.owner  = THIS_MODULE,

Drop this line.

Cheers,
Peter

> +		.of_match_table = of_match_ptr(i2cs_mux_of_match),
> +	},
> +	.probe = i2cs_mux_probe,
> +	.remove = i2cs_mux_remove,
> +};
> +module_platform_driver(i2cs_mux_driver);
> +
> +MODULE_DESCRIPTION("Juniper Networks I2CS RE Mux driver");
> +MODULE_AUTHOR("Georgi Vlaev <gvlaev@...iper.net>");
> +MODULE_LICENSE("GPL");
> +MODULE_ALIAS("platform:i2c-mux-i2cs");
> 

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