linux-kernel - Re: [PATCH] i801_smbus: clear SMBALERT status bit and disable SMBALERT interrupt

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Message-ID: <435ec740-dbfd-8c00-2472-35a49d273822@nokia.com>
Date:   Tue, 17 Sep 2019 11:37:34 +0000
From:   "Sverdlin, Alexander (Nokia - DE/Ulm)" <alexander.sverdlin@...ia.com>
To:     Jean Delvare <jdelvare@...e.de>,
        "Xu, Lingyan (NSB - CN/Hangzhou)" <lingyan.xu@...ia-sbell.com>
CC:     "Adamski, Krzysztof (Nokia - PL/Wroclaw)" 
        <krzysztof.adamski@...ia.com>,
        "Wiebe, Wladislav (Nokia - DE/Ulm)" <wladislav.wiebe@...ia.com>,
        "linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] i801_smbus: clear SMBALERT status bit and disable
 SMBALERT interrupt

Hello Jean,

On 05/09/2019 14:57, Jean Delvare wrote:
> If this is of any value to you, I tried implementing it in i2c-i801 a
> few days ago. I can't really test it though as I don't have any device
> which triggers an alert on my system, but I am sharing it with you if
> you want to give it a try. You would still need to write the code in
> the slave driver.
> 
> ---
>  drivers/i2c/busses/i2c-i801.c |   77 +++++++++++++++++++++++++++++++++++++-----
>  1 file changed, 69 insertions(+), 8 deletions(-)
> 
> --- linux-5.2.orig/drivers/i2c/busses/i2c-i801.c	2019-08-28 15:58:52.725828215 +0200
> +++ linux-5.2/drivers/i2c/busses/i2c-i801.c	2019-08-28 16:50:09.212696037 +0200
> @@ -196,6 +196,7 @@
>  
>  /* Host Notify Command register bits */
>  #define SMBSLVCMD_HST_NTFY_INTREN	BIT(0)
> +#define SMBSLVCMD_SMBALERT_DIS		BIT(2)
>  
>  #define STATUS_ERROR_FLAGS	(SMBHSTSTS_FAILED | SMBHSTSTS_BUS_ERR | \
>  				 SMBHSTSTS_DEV_ERR)
> @@ -281,6 +282,10 @@ struct i801_priv {
>  	 */
>  	bool acpi_reserved;
>  	struct mutex acpi_lock;
> +
> +	/* SMBus alert */
> +	struct i2c_smbus_alert_setup alert_data;
> +	struct i2c_client *ara;
>  };
>  
>  #define FEATURE_SMBUS_PEC	BIT(0)
> @@ -289,6 +294,7 @@ struct i801_priv {
>  #define FEATURE_I2C_BLOCK_READ	BIT(3)
>  #define FEATURE_IRQ		BIT(4)
>  #define FEATURE_HOST_NOTIFY	BIT(5)
> +#define FEATURE_SMBUS_ALERT	BIT(6)
>  /* Not really a feature, but it's convenient to handle it as such */
>  #define FEATURE_IDF		BIT(15)
>  #define FEATURE_TCO_SPT		BIT(16)
> @@ -301,6 +307,7 @@ static const char *i801_feature_names[]
>  	"I2C block read",
>  	"Interrupt",
>  	"SMBus Host Notify",
> +	"SMBus Alert",
>  };
>  
>  static unsigned int disable_features;
> @@ -310,7 +317,8 @@ MODULE_PARM_DESC(disable_features, "Disa
>  	"\t\t  0x02  disable the block buffer\n"
>  	"\t\t  0x08  disable the I2C block read functionality\n"
>  	"\t\t  0x10  don't use interrupts\n"
> -	"\t\t  0x20  disable SMBus Host Notify ");
> +	"\t\t  0x20  disable SMBus Host Notify\n"
> +	"\t\t  0x40  disable SMBus Alert ");
>  
>  /* Make sure the SMBus host is ready to start transmitting.
>     Return 0 if it is, -EBUSY if it is not. */
> @@ -620,8 +628,24 @@ static irqreturn_t i801_host_notify_isr(
>  	return IRQ_HANDLED;
>  }
>  
> +static irqreturn_t i801_smbus_alert_isr(struct i801_priv *priv)
> +{
> +	struct i2c_client *ara = priv->ara;
> +
> +	if (ara) {
> +		dev_dbg(&ara->dev, "SMBus alert received\n");
> +		i2c_handle_smbus_alert(ara);

I've just tested this approach and must conclude that it doesn't work.
Seems that SMBALERT# in i801 is level-triggered (I wasn't able to
confirm or decline this statement using i801 documentation) and
once SMBALERT# is triggered, I experience the interrupt flood.
Clearing the interrupt request bit below has no effect at this point.

Unfortunately, current smbalert API doesn't provide any synchronous
interface to test another approach.

> +	} else
> +		dev_dbg(&priv->adapter.dev,
> +			"SMBus alert received but no ARA client!\n");
> +
> +	/* clear SMBus Alert bit and return */
> +	outb_p(SMBHSTSTS_SMBALERT_STS, SMBHSTSTS(priv));
> +	return IRQ_HANDLED;
> +}
> +
>  /*
> - * There are three kinds of interrupts:
> + * There are four kinds of interrupts:
>   *
>   * 1) i801 signals transaction completion with one of these interrupts:
>   *      INTR - Success

Therefore, I'd like to ask you (and other I2C maintainers), not that
I spend a time for a solution which has no upstream perspectives, what
shall be the preferred way for i801 driver:

a) We disable SMBALERT# completely

or

b) I export smbus_alert(), so that we can
	- catch the IRQ
	- disable SMBALERT#
	- synchronously smbus_alert()
	- re-enable SMBALERT#

?

-- 
Best regards,
Alexander Sverdlin.