linux-kernel - Re: applesmc oops in 3.10/3.11

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Date:	Mon, 07 Oct 2013 16:42:11 -0700
From:	Guenter Roeck <linux@...ck-us.net>
To:	Henrik Rydberg <rydberg@...omail.se>
CC:	Chris Murphy <bugzilla@...orremedies.com>,
	Josh Boyer <jwboyer@...oraproject.org>, khali@...ux-fr.org,
	lm-sensors@...sensors.org,
	"Linux-Kernel@...r. Kernel. Org" <linux-kernel@...r.kernel.org>
Subject: Re: applesmc oops in 3.10/3.11

On 10/02/2013 10:24 AM, Henrik Rydberg wrote:

>>>From 4451da32414080bd0563ee9e061f19bf90463cc5 Mon Sep 17 00:00:00 2001
> From: Henrik Rydberg <rydberg@...omail.se>
> Date: Wed, 2 Oct 2013 19:15:03 +0200
> Subject: [PATCH] applesmc remedy take 2
>
> Conjectured problem: there are remnant bytes ready on the data line
> which corrupts the read after a failure.
>
> Remedy: assuming bit0 is the read valid line, try to flush it before
> starting a new command.
>
> Tests by Chris suggests reading the status is enough for the problem
> to go away, which is consistent with a change in the SMC interface,
> where the number of bytes to read is no longer specified, but found
> out by reading until end of data.
>
> Tested on a MacBookAir3,1, but the original problem has not been
> reproduced.

So, what should we do with this patch ? Apply it ?

Thanks,
Guenter

> ---
>   drivers/hwmon/applesmc.c | 13 +++++++++++++
>   1 file changed, 13 insertions(+)
>
> diff --git a/drivers/hwmon/applesmc.c b/drivers/hwmon/applesmc.c
> index 98814d1..c0ff350 100644
> --- a/drivers/hwmon/applesmc.c
> +++ b/drivers/hwmon/applesmc.c
> @@ -230,6 +230,7 @@ static int send_argument(const char *key)
>
>   static int read_smc(u8 cmd, const char *key, u8 *buffer, u8 len)
>   {
> +	u8 status, data;
>   	int i;
>
>   	if (send_command(cmd) || send_argument(key)) {
> @@ -237,6 +238,7 @@ static int read_smc(u8 cmd, const char *key, u8 *buffer, u8 len)
>   		return -EIO;
>   	}
>
> +	/* This has no effect on newer (2012) SMCs */
>   	if (send_byte(len, APPLESMC_DATA_PORT)) {
>   		pr_warn("%.4s: read len fail\n", key);
>   		return -EIO;
> @@ -250,6 +252,17 @@ static int read_smc(u8 cmd, const char *key, u8 *buffer, u8 len)
>   		buffer[i] = inb(APPLESMC_DATA_PORT);
>   	}
>
> +	/* Read the data port until bit0 is cleared */
> +	for (i = 0; i < 16; i++) {
> +		udelay(APPLESMC_MIN_WAIT);
> +		status = inb(APPLESMC_CMD_PORT);
> +		if (!(status & 0x01))
> +			break;
> +		data = inb(APPLESMC_DATA_PORT);
> +	}
> +	if (i)
> +		pr_warn("flushed %d bytes, last value is: %d\n", i, data);
> +
>   	return 0;
>   }
>
>

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