Date:   Sat, 19 Mar 2022 15:41:02 +0100
From:   Peter Rosin <peda@...ntia.se>
To:     Patrick Rudolph <patrick.rudolph@...ements.com>
Cc:     linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [v6 2/3] i2c: muxes: pca954x: Add MAX735x/MAX736x support

Hi!

Sorry for the slow review and thanks for your patience...

On 2022-02-16 08:46, Patrick Rudolph wrote:
> Add support for the following Maxim chips using the existing PCA954x
> driver:
> - MAX7356
> - MAX7357
> - MAX7358
> - MAX7367
> - MAX7368
> - MAX7369
> 
> All added Maxim chips behave like the PCA954x, where a single SMBUS byte
> write selects up to 8 channels to be bridged to the primary bus.
> 
> The MAX7357 exposes 6 additional registers at Power-On-Reset and is

MAX7358 also has the same enhanced mode as the 7357, no?

And what do you mean that they are exposed at POR? I can see why they
are not exposed /before/ POR, but are they ever /not/ exposed? If they
are always exposed when the chip is "alive", then I suggest that the
POR wording is dropped, otherwise that the above is reworded to
describe when the register are no longer exposed.

> configured to:
>  - Disabled interrupts on bus locked up detection
>  - Enable bus locked-up clearing
>  - Disconnect only locked bus instead of all channels
> 
> While the MAX7357/MAX7358 have interrupt support, they don't act as
> interrupt controller like the PCA9545 does. Thus don't enable IRQ support
> and handle them like the PCA9548.
> 
> Tested using the MAX7357 and verified that the stalled bus is disconnected
> while the other channels remain operational.
> 
> Signed-off-by: Patrick Rudolph <patrick.rudolph@...ements.com>
> ---
>  drivers/i2c/muxes/Kconfig           |  4 +-
>  drivers/i2c/muxes/i2c-mux-pca954x.c | 92 +++++++++++++++++++++++++++--
>  2 files changed, 90 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/i2c/muxes/Kconfig b/drivers/i2c/muxes/Kconfig
> index 1708b1a82da2..2ac99d044199 100644
> --- a/drivers/i2c/muxes/Kconfig
> +++ b/drivers/i2c/muxes/Kconfig
> @@ -65,11 +65,11 @@ config I2C_MUX_PCA9541
>  	  will be called i2c-mux-pca9541.
>  
>  config I2C_MUX_PCA954x
> -	tristate "NXP PCA954x and PCA984x I2C Mux/switches"
> +	tristate "NXP PCA954x/PCA984x and Maxim MAX735x/MAX736x I2C Mux/switches"
>  	depends on GPIOLIB || COMPILE_TEST
>  	help
>  	  If you say yes here you get support for the NXP PCA954x
> -	  and PCA984x I2C mux/switch devices.
> +	  and PCA984x and Maxim MAX735x/MAX736x I2C mux/switch devices.

and and and... :-) Maybe like this?

	  If you say yes here you get support for NXP PCA954x/PCA984x
	  and Maxim MAX735x/MAX736x I2C mux/switch devices.

>  	  This driver can also be built as a module.  If so, the module
>  	  will be called i2c-mux-pca954x.
> diff --git a/drivers/i2c/muxes/i2c-mux-pca954x.c b/drivers/i2c/muxes/i2c-mux-pca954x.c
> index 4ad665757dd8..33b9a6a1fffa 100644
> --- a/drivers/i2c/muxes/i2c-mux-pca954x.c
> +++ b/drivers/i2c/muxes/i2c-mux-pca954x.c
> @@ -4,6 +4,7 @@
>   *
>   * Copyright (c) 2008-2009 Rodolfo Giometti <giometti@...ux.it>
>   * Copyright (c) 2008-2009 Eurotech S.p.A. <info@...otech.it>
> + * Copyright (c) 2022 Patrick Rudolph <patrick.rudolph@...ements.com>
>   *
>   * This module supports the PCA954x and PCA984x series of I2C multiplexer/switch
>   * chips made by NXP Semiconductors.
> @@ -11,6 +12,12 @@
>   *	 PCA9540, PCA9542, PCA9543, PCA9544, PCA9545, PCA9546, PCA9547,
>   *	 PCA9548, PCA9846, PCA9847, PCA9848 and PCA9849.
>   *
> + * It's also compatible to Maxims MAX735x I2C switch chips, which are controlled
> + * as the NXP PCA9548 and the MAX736x chips that act like the PCA9544.
> + *
> + * This includes the:
> + *	 MAX7356, MAX7357, MAX7358, MAX7367, MAX7368 and MAX7369
> + *
>   * These chips are all controlled via the I2C bus itself, and all have a
>   * single 8-bit register. The upstream "parent" bus fans out to two,
>   * four, or eight downstream busses or channels; which of these
> @@ -50,7 +57,30 @@
>  
>  #define PCA954X_IRQ_OFFSET 4
>  
> +/*
> + * MAX7357 exposes 7 registers on POR which allow to configure additional
> + * features. Disable interrupts, enable bus locked-up clearing,
> + * isolate only the locked channel instead of all channels.

Same MAX7358 and POR comments as above.

The way I understands things are:

 * MAX7357/MAX7358 exposes 7 registers which allow setup of
 * enhanced mode features. The first of these registers is the
 * switch control register that is present in some form on all
 * chips supported by this driver.
 * The second register is the configuration register, which allows
 * to configure additional features. E.g. disable interrupts,
 * enable bus locked-up clearing and isolate only the locked
 * channel instead of all channels.
 * The remaining 5 registers are left as is by this driver.

> + */
> +#define MAX7357_CONF_INT_ENABLE			BIT(0)
> +#define MAX7357_CONF_FLUSH_OUT			BIT(1)
> +#define MAX7357_CONF_RELEASE_INT		BIT(2)
> +#define MAX7357_CONF_LOCK_UP_CLEAR		BIT(3)
> +#define MAX7357_CONF_DISCON_SINGLE_CHAN		BIT(4)
> +#define MAX7357_CONF_BUS_LOCKUP_DETECTION	BIT(5)
> +#define MAX7357_CONF_ENABLE_BASIC_MODE		BIT(6)
> +#define MAX7357_CONF_PRECONNECT_TEST		BIT(7)
> +
> +#define MAX7357_CONF_DEFAULTS (MAX7357_CONF_FLUSH_OUT | \
> +	 MAX7357_CONF_DISCON_SINGLE_CHAN)
> +
>  enum pca_type {
> +	max_7367,
> +	max_7368,
> +	max_7369,
> +	max_7356,
> +	max_7357,
> +	max_7358,
>  	pca_9540,
>  	pca_9542,
>  	pca_9543,
> @@ -69,6 +99,7 @@ struct chip_desc {
>  	u8 nchans;
>  	u8 enable;	/* used for muxes only */
>  	u8 has_irq;
> +	u8 max7357;

Perhaps maxim_enhanced_mode is a better name?

>  	enum muxtype {
>  		pca954x_ismux = 0,
>  		pca954x_isswi
> @@ -90,8 +121,42 @@ struct pca954x {
>  	raw_spinlock_t lock;
>  };
>  
> -/* Provide specs for the PCA954x types we know about */
> +/* Provide specs for the PCA954x and MAX735x types we know about */
>  static const struct chip_desc chips[] = {
> +	[max_7356] = {
> +		.nchans = 8,
> +		.muxtype = pca954x_isswi,
> +		.id = { .manufacturer_id = I2C_DEVICE_ID_NONE },
> +	},
> +	[max_7357] = {
> +		.nchans = 8,
> +		.muxtype = pca954x_isswi,
> +		.max7357 = 1,
> +		.id = { .manufacturer_id = I2C_DEVICE_ID_NONE },
> +	},
> +	[max_7358] = {
> +		.nchans = 8,
> +		.muxtype = pca954x_isswi,
> +		.id = { .manufacturer_id = I2C_DEVICE_ID_NONE },
> +	},
> +	[max_7367] = {
> +		.nchans = 4,
> +		.muxtype = pca954x_isswi,
> +		.has_irq = 1,
> +		.id = { .manufacturer_id = I2C_DEVICE_ID_NONE },
> +	},
> +	[max_7368] = {
> +		.nchans = 4,
> +		.muxtype = pca954x_isswi,
> +		.id = { .manufacturer_id = I2C_DEVICE_ID_NONE },
> +	},
> +	[max_7369] = {
> +		.nchans = 4,
> +		.enable = 0x4,
> +		.muxtype = pca954x_ismux,
> +		.has_irq = 1,
> +		.id = { .manufacturer_id = I2C_DEVICE_ID_NONE },
> +	},
>  	[pca_9540] = {
>  		.nchans = 2,
>  		.enable = 0x4,
> @@ -177,6 +242,12 @@ static const struct chip_desc chips[] = {
>  };
>  
>  static const struct i2c_device_id pca954x_id[] = {
> +	{ "max7356", max_7356 },
> +	{ "max7357", max_7357 },
> +	{ "max7358", max_7358 },
> +	{ "max7367", max_7367 },
> +	{ "max7368", max_7368 },
> +	{ "max7369", max_7369 },
>  	{ "pca9540", pca_9540 },
>  	{ "pca9542", pca_9542 },
>  	{ "pca9543", pca_9543 },
> @@ -194,6 +265,12 @@ static const struct i2c_device_id pca954x_id[] = {
>  MODULE_DEVICE_TABLE(i2c, pca954x_id);
>  
>  static const struct of_device_id pca954x_of_match[] = {
> +	{ .compatible = "maxim,max7356", .data = &chips[max_7356] },
> +	{ .compatible = "maxim,max7357", .data = &chips[max_7357] },
> +	{ .compatible = "maxim,max7358", .data = &chips[max_7358] },
> +	{ .compatible = "maxim,max7367", .data = &chips[max_7367] },
> +	{ .compatible = "maxim,max7368", .data = &chips[max_7368] },
> +	{ .compatible = "maxim,max7369", .data = &chips[max_7369] },
>  	{ .compatible = "nxp,pca9540", .data = &chips[pca_9540] },
>  	{ .compatible = "nxp,pca9542", .data = &chips[pca_9542] },
>  	{ .compatible = "nxp,pca9543", .data = &chips[pca_9543] },
> @@ -401,9 +478,16 @@ static int pca954x_init(struct i2c_client *client, struct pca954x *data)
>  	else
>  		data->last_chan = 0; /* Disconnect multiplexer */
>  
> -	ret = i2c_smbus_write_byte(client, data->last_chan);
> -	if (ret < 0)
> -		data->last_chan = 0;
> +	if (data->chip->max7357) {
> +		ret = i2c_smbus_write_byte_data(client, data->last_chan,
> +						MAX7357_CONF_DEFAULTS);
> +		if (ret < 0)
> +			data->last_chan = 0;
> +	} else {
> +		ret = i2c_smbus_write_byte(client, data->last_chan);
> +		if (ret < 0)
> +			data->last_chan = 0;
> +	}
>  
>  	return ret;
>  }

The actual code is simple enough, and looks good.

Cheers,
Peter

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