linux-kernel - Re: [PATCH v3 06/11] iio: light: cm32181: Handle CM3218 ACPI devices with 2 I2C resources

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Date:   Sun, 3 May 2020 12:04:39 +0100
From:   Jonathan Cameron <jic23@...nel.org>
To:     Hans de Goede <hdegoede@...hat.com>
Cc:     "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Len Brown <lenb@...nel.org>,
        Darren Hart <dvhart@...radead.org>,
        Andy Shevchenko <andy@...radead.org>,
        linux-acpi@...r.kernel.org, platform-driver-x86@...r.kernel.org,
        linux-kernel@...r.kernel.org, Hartmut Knaack <knaack.h@....de>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Peter Meerwald-Stadler <pmeerw@...erw.net>,
        linux-iio@...r.kernel.org
Subject: Re: [PATCH v3 06/11] iio: light: cm32181: Handle CM3218 ACPI
 devices with 2 I2C resources

On Tue, 28 Apr 2020 19:29:18 +0200
Hans de Goede <hdegoede@...hat.com> wrote:

> Some ACPI systems list 2 I2C resources for the CM3218 sensor. On these
> systems the first I2cSerialBus ACPI-resource points to the SMBus Alert
> Response Address (ARA, 0x0c) and the second I2cSerialBus ACPI-resource
> points to the actual CM3218 sensor address:
> 
>  Method (_CRS, 0, NotSerialized)  // _CRS: Current Resource Settings
>  {
>      Name (SBUF, ResourceTemplate ()
>      {

I have a vague recollection that we had case of this where they could
come in either order.  Could that happen here?

My mind may be playing tricks on me of course and that may never
happen...

Did I ever mention how much the lack of spec for some of these corner
cases annoys me?

J

>          I2cSerialBusV2 (0x000C, ControllerInitiated, 0x00061A80,
>              AddressingMode7Bit, "\\_SB.I2C3",
>              0x00, ResourceConsumer, , Exclusive,
>              )
>          I2cSerialBusV2 (0x0048, ControllerInitiated, 0x00061A80,
>              AddressingMode7Bit, "\\_SB.I2C3",
>              0x00, ResourceConsumer, , Exclusive,
>              )
>          Interrupt (ResourceConsumer, Level, ActiveHigh, Exclusive, ,, )
>          {
>              0x00000033,
>          }
>      })
>      Return (SBUF) /* \_SB_.I2C3.ALSD._CRS.SBUF */
>  }
> 
> Detect this and take the following step to deal with it:
> 
> 1. When a SMBus Alert capable sensor has an Alert asserted, it will
>    not respond on its actual I2C address. Read a byte from the ARA
>    to clear any pending Alerts.
> 
> 2. Create a "dummy" client for the actual I2C address and
>    use that client to communicate with the sensor.
> 
> Signed-off-by: Hans de Goede <hdegoede@...hat.com>
> ---
> Changes in v3:
> - Create and use a dummy client instead of relying on i2c-multi-instantiate
>   to create 2 separate clients for the 2 I2C resources
> 
> Changes in v2
> - s/i2c_client-s/I2C clients/ in added comment
> ---
>  drivers/iio/light/cm32181.c | 22 ++++++++++++++++++++++
>  1 file changed, 22 insertions(+)
> 
> diff --git a/drivers/iio/light/cm32181.c b/drivers/iio/light/cm32181.c
> index 8fe49610fc26..c23a5c3a86a3 100644
> --- a/drivers/iio/light/cm32181.c
> +++ b/drivers/iio/light/cm32181.c
> @@ -51,6 +51,8 @@
>  #define CM32181_CALIBSCALE_RESOLUTION	1000
>  #define MLUX_PER_LUX			1000
>  
> +#define SMBUS_ALERT_RESPONSE_ADDRESS	0x0c
> +
>  static const u8 cm32181_reg[CM32181_CONF_REG_NUM] = {
>  	CM32181_REG_ADDR_CMD,
>  };
> @@ -335,6 +337,26 @@ static int cm32181_probe(struct i2c_client *client)
>  	if (!indio_dev)
>  		return -ENOMEM;
>  
> +	/*
> +	 * Some ACPI systems list 2 I2C resources for the CM3218 sensor, the
> +	 * SMBus Alert Response Address (ARA, 0x0c) and the actual I2C address.
> +	 * Detect this and take the following step to deal with it:
> +	 * 1. When a SMBus Alert capable sensor has an Alert asserted, it will
> +	 *    not respond on its actual I2C address. Read a byte from the ARA
> +	 *    to clear any pending Alerts.
> +	 * 2. Create a "dummy" client for the actual I2C address and
> +	 *    use that client to communicate with the sensor.
> +	 */
> +	if (ACPI_HANDLE(dev) && client->addr == SMBUS_ALERT_RESPONSE_ADDRESS) {
> +		struct i2c_board_info board_info = { .type = "dummy" };
> +
> +		i2c_smbus_read_byte(client);
> +
> +		client = i2c_acpi_new_device(dev, 1, &board_info);
> +		if (IS_ERR(client))
> +			return PTR_ERR(client);
> +	}
> +
>  	cm32181 = iio_priv(indio_dev);
>  	cm32181->client = client;
>