Date:   Thu, 5 Jan 2017 09:54:19 +0100
From:   Pali Rohár <pali.rohar@...il.com>
To:     Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:     Wolfram Sang <wsa@...-dreams.de>,
        Benjamin Tissoires <benjamin.tissoires@...hat.com>,
        Michał Kępień <kernel@...pniu.pl>,
        Jean Delvare <jdelvare@...e.com>,
        Steven Honeyman <stevenhoneyman@...il.com>,
        Valdis.Kletnieks@...edu,
        Jochen Eisinger <jochen@...guin-breeder.org>,
        Gabriele Mazzotta <gabriele.mzt@...il.com>,
        Andy Lutomirski <luto@...nel.org>, Mario_Limonciello@...l.com,
        Alex Hung <alex.hung@...onical.com>,
        Takashi Iwai <tiwai@...e.de>, linux-i2c@...r.kernel.org,
        linux-kernel@...r.kernel.org, platform-driver-x86@...r.kernel.org
Subject: Re: [PATCH] i2c: i801: Register optional lis3lv02d i2c device on
 Dell machines

On Wednesday 04 January 2017 09:54:56 Dmitry Torokhov wrote:
> On Wed, Jan 04, 2017 at 06:46:19PM +0100, Wolfram Sang wrote:
> > 
> > > How about:
> > > ---
> > > From daa7571bbf337704332c0cfeec9b8fd5aeae596f Mon Sep 17 00:00:00 2001
> > > From: Benjamin Tissoires <benjamin.tissoires@...hat.com>
> > > Date: Wed, 4 Jan 2017 18:26:54 +0100
> > > Subject: [PATCH] I2C: add the source of the IRQ in struct i2c_client
> > > 
> > > With commit 4d5538f5882a ("i2c: use an IRQ to report Host Notify events,
> > > not alert"), the IRQ provided in struct i2c_client might be assigned while
> > > it has not been explicitly declared by either the platform information
> > > or OF or ACPI.
> > > Some drivers (lis3lv02d) rely on the fact that the IRQ gets assigned or
> > > not to trigger a different behavior (exposing /dev/freefall in this case).
> > > 
> > > Provide a way for others to know who set the IRQ and so they can behave
> > > accordingly.
> > > 
> > > Signed-off-by: Benjamin Tissoires <benjamin.tissoires@...hat.com>
> > > ---
> > >  drivers/i2c/i2c-core.c |  7 +++++++
> > >  include/linux/i2c.h    | 11 +++++++++++
> > >  2 files changed, 18 insertions(+)
> > > 
> > > diff --git a/drivers/i2c/i2c-core.c b/drivers/i2c/i2c-core.c
> > > index cf9e396..226c75d 100644
> > > --- a/drivers/i2c/i2c-core.c
> > > +++ b/drivers/i2c/i2c-core.c
> > > @@ -935,8 +935,12 @@ static int i2c_device_probe(struct device *dev)
> > >  			irq = of_irq_get_byname(dev->of_node, "irq");
> > >  			if (irq == -EINVAL || irq == -ENODATA)
> > >  				irq = of_irq_get(dev->of_node, 0);
> > > +			if (irq > 0)
> > > +				client->irq_source = I2C_IRQ_SOURCE_OF;
> > >  		} else if (ACPI_COMPANION(dev)) {
> > >  			irq = acpi_dev_gpio_irq_get(ACPI_COMPANION(dev), 0);
> > > +			if (irq > 0)
> > > +				client->irq_source = I2C_IRQ_SOURCE_ACPI;
> > >  		}
> > >  		if (irq == -EPROBE_DEFER)
> > >  			return irq;
> > > @@ -947,6 +951,8 @@ static int i2c_device_probe(struct device *dev)
> > >  		if (irq < 0) {
> > >  			dev_dbg(dev, "Using Host Notify IRQ\n");
> > >  			irq = i2c_smbus_host_notify_to_irq(client);
> > > +			if (irq > 0)
> > > +				client->irq_source = I2C_IRQ_SOURCE_HOST_NOTIFY;
> > >  		}
> > >  		if (irq < 0)
> > >  			irq = 0;
> > > @@ -1317,6 +1323,7 @@ i2c_new_device(struct i2c_adapter *adap, struct i2c_board_info const *info)
> > >  	client->flags = info->flags;
> > >  	client->addr = info->addr;
> > >  	client->irq = info->irq;
> > > +	client->irq_source = I2C_IRQ_SOURCE_PLATFORM;
> > >  
> > >  	strlcpy(client->name, info->type, sizeof(client->name));
> > >  
> > > diff --git a/include/linux/i2c.h b/include/linux/i2c.h
> > > index b2109c5..7d0368d 100644
> > > --- a/include/linux/i2c.h
> > > +++ b/include/linux/i2c.h
> > > @@ -213,6 +213,13 @@ struct i2c_driver {
> > >  };
> > >  #define to_i2c_driver(d) container_of(d, struct i2c_driver, driver)
> > >  
> > > +enum i2c_irq_source {
> > > +	I2C_IRQ_SOURCE_PLATFORM,
> > > +	I2C_IRQ_SOURCE_OF,
> > > +	I2C_IRQ_SOURCE_ACPI,
> > > +	I2C_IRQ_SOURCE_HOST_NOTIFY,
> > > +};
> > > +
> > >  /**
> > >   * struct i2c_client - represent an I2C slave device
> > >   * @flags: I2C_CLIENT_TEN indicates the device uses a ten bit chip address;
> > > @@ -227,6 +234,9 @@ struct i2c_driver {
> > >   *	userspace_devices list
> > >   * @slave_cb: Callback when I2C slave mode of an adapter is used. The adapter
> > >   *	calls it to pass on slave events to the slave driver.
> > > + * @irq_source: Enum which provides the source of the IRQ. Useful to know
> > > + * 	if the IRQ was issued from Host Notify or if it was provided by an other
> > > + * 	component.
> > 
> > I'd think some documentation somewhere makes sense why we need to
> > distinguish this in some cases?
> 
> I'd rather drivers be oblivious of the source of interrupt. If they need
> to distinguish between them that means that our IRQ abstration failed.
> 
> > 
> > >   *
> > >   * An i2c_client identifies a single device (i.e. chip) connected to an
> > >   * i2c bus. The behaviour exposed to Linux is defined by the driver
> > > @@ -245,6 +255,7 @@ struct i2c_client {
> > >  #if IS_ENABLED(CONFIG_I2C_SLAVE)
> > >  	i2c_slave_cb_t slave_cb;	/* callback for slave mode	*/
> > >  #endif
> > > +	enum i2c_irq_source irq_source;	/* which component assigned the irq */
> > >  };
> > >  #define to_i2c_client(d) container_of(d, struct i2c_client, dev)
> > > 
> > > Dmitry, Wolfram, Jean, would this be acceptable for you?
> > 
> > Adding something to i2c_driver is not exactly cheap, but from what I
> > glimpsed from this thread, this is one of the cleanest solution to this
> > problem?
> > 
> 
> As Benjamin said, it is really property of device [instance], not
> driver. I.e. driver could handle both wired IRQ and HostNotify-based
> scheme similarly, it is device (and board) that knows how stuff is
> connected.
> 
> Maybe we could do something like this (untested):
> 
> 
> From e362a0277fd1bd6112f258664d8831d9bc6b78da Mon Sep 17 00:00:00 2001
> From: Dmitry Torokhov <dmitry.torokhov@...il.com>
> Date: Wed, 4 Jan 2017 09:33:43 -0800
> Subject: [PATCH] i2c: do not enable fall back to Host Notify by default
> 
> Falling back unconditionally to HostNotify as primary client's interrupt
> breaks some drivers which alter their functionality depending on whether
> interrupt is present or not, so let's introduce a board flag telling I2C
> core explicitly if we want wired interrupt or HostNotify-based one:
> I2C_CLIENT_HOST_NOTIFY.
> 
> For DT-based systems we introduce "host-notofy" property that we convert
> to I2C_CLIENT_HOST_NOTIFY board flag.
> 
> Signed-off-by: Dmitry Torokhov <dmitry.torokhov@...il.com>
> ---
>  Documentation/devicetree/bindings/i2c/i2c.txt |  8 ++++++++
>  drivers/i2c/i2c-core.c                        | 17 ++++++++---------
>  include/linux/i2c.h                           |  1 +
>  3 files changed, 17 insertions(+), 9 deletions(-)
> 
> diff --git a/Documentation/devicetree/bindings/i2c/i2c.txt b/Documentation/devicetree/bindings/i2c/i2c.txt
> index 5fa691e6f638..cee9d5055fa2 100644
> --- a/Documentation/devicetree/bindings/i2c/i2c.txt
> +++ b/Documentation/devicetree/bindings/i2c/i2c.txt
> @@ -62,6 +62,9 @@ wants to support one of the below features, it should adapt the bindings below.
>  	"irq" and "wakeup" names are recognized by I2C core, other names are
>  	left to individual drivers.
>  
> +- host-notify
> +	device uses SMBus host notify protocol instead of interrupt line.
> +
>  - multi-master
>  	states that there is another master active on this bus. The OS can use
>  	this information to adapt power management to keep the arbitration awake
> @@ -81,6 +84,11 @@ Binding may contain optional "interrupts" property, describing interrupts
>  used by the device. I2C core will assign "irq" interrupt (or the very first
>  interrupt if not using interrupt names) as primary interrupt for the slave.
>  
> +Alternatively, devices supporting SMbus Host Notify, and connected to
> +adapters that support this feature, may use "host-notify" property. I2C
> +core will create a virtual interrupt for Host Notify and assign it as
> +primary interrupt for the slave.
> +
>  Also, if device is marked as a wakeup source, I2C core will set up "wakeup"
>  interrupt for the device. If "wakeup" interrupt name is not present in the
>  binding, then primary interrupt will be used as wakeup interrupt.
> diff --git a/drivers/i2c/i2c-core.c b/drivers/i2c/i2c-core.c
> index cf9e396d7702..250969fa7670 100644
> --- a/drivers/i2c/i2c-core.c
> +++ b/drivers/i2c/i2c-core.c
> @@ -931,7 +931,10 @@ static int i2c_device_probe(struct device *dev)
>  	if (!client->irq) {
>  		int irq = -ENOENT;
>  
> -		if (dev->of_node) {
> +		if (client->flags & I2C_CLIENT_HOST_HOTIFY) {
> +			dev_dbg(dev, "Using Host Notify IRQ\n");
> +			irq = i2c_smbus_host_notify_to_irq(client);
> +		} else if (dev->of_node) {
>  			irq = of_irq_get_byname(dev->of_node, "irq");
>  			if (irq == -EINVAL || irq == -ENODATA)
>  				irq = of_irq_get(dev->of_node, 0);
> @@ -940,14 +943,7 @@ static int i2c_device_probe(struct device *dev)
>  		}
>  		if (irq == -EPROBE_DEFER)
>  			return irq;
> -		/*
> -		 * ACPI and OF did not find any useful IRQ, try to see
> -		 * if Host Notify can be used.
> -		 */
> -		if (irq < 0) {
> -			dev_dbg(dev, "Using Host Notify IRQ\n");
> -			irq = i2c_smbus_host_notify_to_irq(client);
> -		}
> +
>  		if (irq < 0)
>  			irq = 0;
>  
> @@ -1716,6 +1712,9 @@ static struct i2c_client *of_i2c_register_device(struct i2c_adapter *adap,
>  	info.of_node = of_node_get(node);
>  	info.archdata = &dev_ad;
>  
> +	if (of_read_property_bool(node, "host-notify"))
> +		info.flags |= I2C_CLIENT_HOST_NOTIFY;
> +
>  	if (of_get_property(node, "wakeup-source", NULL))
>  		info.flags |= I2C_CLIENT_WAKE;
>  
> diff --git a/include/linux/i2c.h b/include/linux/i2c.h
> index b2109c522dec..4b45ec46161f 100644
> --- a/include/linux/i2c.h
> +++ b/include/linux/i2c.h
> @@ -665,6 +665,7 @@ i2c_unlock_adapter(struct i2c_adapter *adapter)
>  #define I2C_CLIENT_TEN		0x10	/* we have a ten bit chip address */
>  					/* Must equal I2C_M_TEN below */
>  #define I2C_CLIENT_SLAVE	0x20	/* we are the slave */
> +#define I2C_CLIENT_HOST_NOTIFY	0x40	/* We want to use I2C host notify */
>  #define I2C_CLIENT_WAKE		0x80	/* for board_info; true iff can wake */
>  #define I2C_CLIENT_SCCB		0x9000	/* Use Omnivision SCCB protocol */
>  					/* Must match I2C_M_STOP|IGNORE_NAK */
> -- 
> 2.11.0.390.gc69c2f50cf-goog
> 
> 

Looks good, this seems to be elegant solution to our problem.

But then it is needed to patch those touchpad drivers to add that
I2C_CLIENT_HOST_NOTIFY flag, right?

-- 
Pali Rohár
pali.rohar@...il.com

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