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Subject: Re: [PATCH v3] applesmc: Re-work SMC comms
To:     Henrik Rydberg <rydberg@bitmath.org>,
        Andreas Kemnade <andreas@kemnade.info>
Cc:     Arnd Bergmann <arnd@arndb.de>, linux-hwmon@vger.kernel.org,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        hns@goldelico.com, Guenter Roeck <linux@roeck-us.net>,
        Jean Delvare <jdelvare@suse.com>
References: <70331f82-35a1-50bd-685d-0b06061dd213@fnarfbargle.com>
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 <6d071547-10ee-ca92-ec8b-4b5069d04501@bitmath.org>
 <8e117844-d62a-bcb1-398d-c59cc0d4b878@fnarfbargle.com>
 <e5a856b1-fb1a-db5d-0fde-c86d0bcca1df@bitmath.org>
 <aa60f673-427a-1a47-7593-54d1404c3c92@bitmath.org>
 <9109d059-d9cb-7464-edba-3f42aa78ce92@bitmath.org>
 <5310c0ab-0f80-1f9e-8807-066223edae13@bitmath.org>
 <57057d07-d3a0-8713-8365-7b12ca222bae@fnarfbargle.com>
 <41909045-9486-78d9-76c2-73b99a901b83@bitmath.org>
 <20201108101429.GA28460@mars.bitmath.org>
From:   Brad Campbell <brad@fnarfbargle.com>
Message-ID: <bdabe861-8717-8948-80a0-ca2173c2e22a@fnarfbargle.com>
Date:   Sun, 8 Nov 2020 22:57:17 +1100
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On 8/11/20 9:14 pm, Henrik Rydberg wrote:
> On Sun, Nov 08, 2020 at 09:35:28AM +0100, Henrik Rydberg wrote:
>> Hi Brad,
>>
>> On 2020-11-08 02:00, Brad Campbell wrote:
>>> G'day Henrik,
>>>
>>> I noticed you'd also loosened up the requirement for SMC_STATUS_BUSY in read_smc(). I assume
>>> that causes problems on the early Macbook. This is revised on the one sent earlier.
>>> If you could test this on your Air1,1 it'd be appreciated.
>>
>> No, I managed to screw up the patch; you can see that I carefully added the
>> same treatment for the read argument, being unsure if the BUSY state would
>> remain during the AVAILABLE data phase. I can check that again, but
>> unfortunately the patch in this email shows the same problem.
>>
>> I think it may be worthwhile to rethink the behavior of wait_status() here.
>> If one machine shows no change after a certain status bit change, then
>> perhaps the others share that behavior, and we are waiting in vain. Just
>> imagine how many years of cpu that is, combined. ;-)
> 
> Here is a modification along that line.
> 
> Compared to your latest version, this one has wait_status() return the
> actual status on success. Instead of waiting for BUSY, it waits for
> the other status bits, and checks BUSY afterwards. So as not to wait
> unneccesarily, the udelay() is placed together with the single
> outb(). The return value of send_byte_data() is augmented with
> -EAGAIN, which is then used in send_command() to create the resend
> loop.
> 
> I reach 41 reads per second on the MBA1,1 with this version, which is
> getting close to the performance prior to the problems.

G'day Henrik,

I like this one. It's slower on my laptop (40 rps vs 50 on the MacbookPro11,1) and the same 17 rps on the iMac 12,2 but it's as reliable
and if it works for both of yours then I think it's a winner. I can't really diagnose the iMac properly as I'm 2,800KM away and have
nobody to reboot it if I kill it. 5.7.2 gives 20 rps, so 17 is ok for me.

Andreas, could I ask you to test this one?

Odd my original version worked on your Air3,1 and the other 3 machines without retry.
I wonder how many commands require retries, how many retires are actually required, and what we are going wrong on the Air1,1 that requires
one or more retries. 

I just feels like a brute force approach because there's something we're missing.

> From b4405457f4ba07cff7b7e4f48c47668bee176a25 Mon Sep 17 00:00:00 2001
> From: Brad Campbell <brad@fnarfbargle.com>
> Date: Sun, 8 Nov 2020 12:00:03 +1100
> Subject: [PATCH] hwmon: (applesmc) Re-work SMC comms
> 
> Commit fff2d0f701e6 ("hwmon: (applesmc) avoid overlong udelay()")
> introduced an issue whereby communication with the SMC became
> unreliable with write errors like :
> 
> [  120.378614] applesmc: send_byte(0x00, 0x0300) fail: 0x40
> [  120.378621] applesmc: LKSB: write data fail
> [  120.512782] applesmc: send_byte(0x00, 0x0300) fail: 0x40
> [  120.512787] applesmc: LKSB: write data fail
> 
> The original code appeared to be timing sensitive and was not reliable
> with the timing changes in the aforementioned commit.
> 
> This patch re-factors the SMC communication to remove the timing
> dependencies and restore function with the changes previously
> committed.
> 
> Tested on : MacbookAir6,2 MacBookPro11,1 iMac12,2, MacBookAir1,1,
> MacBookAir3,1
> 
> Fixes: fff2d0f701e6 ("hwmon: (applesmc) avoid overlong udelay()")
> Reported-by: Andreas Kemnade <andreas@kemnade.info>
> Tested-by: Andreas Kemnade <andreas@kemnade.info> # MacBookAir6,2
> Acked-by: Arnd Bergmann <arnd@arndb.de>
> Signed-off-by: Brad Campbell <brad@fnarfbargle.com>
> Signed-off-by: Henrik Rydberg <rydberg@bitmath.org>
> 
> ---
> Changelog : 
> v1 : Inital attempt
> v2 : Address logic and coding style
> v3 : Removed some debug hangover. Added tested-by. Modifications for MacBookAir1,1
> v4 : Do not expect busy state to appear without other state changes
> 
> diff --git a/drivers/hwmon/applesmc.c b/drivers/hwmon/applesmc.c
> index a18887990f4a..ea7c66d5788e 100644
> --- a/drivers/hwmon/applesmc.c
> +++ b/drivers/hwmon/applesmc.c
> @@ -32,6 +32,7 @@
>  #include <linux/hwmon.h>
>  #include <linux/workqueue.h>
>  #include <linux/err.h>
> +#include <linux/bits.h>
>  
>  /* data port used by Apple SMC */
>  #define APPLESMC_DATA_PORT	0x300
> @@ -42,6 +43,11 @@
>  
>  #define APPLESMC_MAX_DATA_LENGTH 32
>  
> +/* Apple SMC status bits */
> +#define SMC_STATUS_AWAITING_DATA  BIT(0) /* SMC has data waiting */
> +#define SMC_STATUS_IB_CLOSED      BIT(1) /* Will ignore any input */
> +#define SMC_STATUS_BUSY           BIT(2) /* Command in progress */
> +
>  /* wait up to 128 ms for a status change. */
>  #define APPLESMC_MIN_WAIT	0x0010
>  #define APPLESMC_RETRY_WAIT	0x0100
> @@ -151,65 +157,78 @@ static unsigned int key_at_index;
>  static struct workqueue_struct *applesmc_led_wq;
>  
>  /*
> - * wait_read - Wait for a byte to appear on SMC port. Callers must
> - * hold applesmc_lock.
> + * Wait for specific status bits with a mask on the SMC
> + * Used before and after writes, and before reads
> + * On success, returns the full status
> + * On failure, returns a negative error
>   */
> -static int wait_read(void)
> +
> +static int wait_status(u8 val, u8 mask)
>  {
>  	unsigned long end = jiffies + (APPLESMC_MAX_WAIT * HZ) / USEC_PER_SEC;
>  	u8 status;
>  	int us;
>  
>  	for (us = APPLESMC_MIN_WAIT; us < APPLESMC_MAX_WAIT; us <<= 1) {
> -		usleep_range(us, us * 16);
>  		status = inb(APPLESMC_CMD_PORT);
> -		/* read: wait for smc to settle */
> -		if (status & 0x01)
> -			return 0;
> +		if ((status & mask) == val)
> +			return status;
>  		/* timeout: give up */
>  		if (time_after(jiffies, end))
>  			break;
> +		usleep_range(us, us * 16);
>  	}
> -
> -	pr_warn("wait_read() fail: 0x%02x\n", status);
>  	return -EIO;
>  }
>  
>  /*
> - * send_byte - Write to SMC port, retrying when necessary. Callers
> + * send_byte_data - Write to SMC data port. Callers
>   * must hold applesmc_lock.
> + * Parameter skip must be true on the last write of any
> + * command or it'll time out.
>   */
> -static int send_byte(u8 cmd, u16 port)
> +
> +static int send_byte_data(u8 cmd, u16 port, bool skip)
>  {
> -	u8 status;
> -	int us;
> -	unsigned long end = jiffies + (APPLESMC_MAX_WAIT * HZ) / USEC_PER_SEC;
> +	int status;
>  
> +	status = wait_status(0, SMC_STATUS_IB_CLOSED);
> +	if (status < 0)
> +		return status;
>  	outb(cmd, port);
> -	for (us = APPLESMC_MIN_WAIT; us < APPLESMC_MAX_WAIT; us <<= 1) {
> -		usleep_range(us, us * 16);
> -		status = inb(APPLESMC_CMD_PORT);
> -		/* write: wait for smc to settle */
> -		if (status & 0x02)
> -			continue;
> -		/* ready: cmd accepted, return */
> -		if (status & 0x04)
> -			return 0;
> -		/* timeout: give up */
> -		if (time_after(jiffies, end))
> -			break;
> -		/* busy: long wait and resend */
> -		udelay(APPLESMC_RETRY_WAIT);
> -		outb(cmd, port);
> -	}
> +	udelay(APPLESMC_MIN_WAIT);
> +	status = wait_status(0, SMC_STATUS_IB_CLOSED);
> +	if (status < 0)
> +		return status;
> +	if (skip || (status & SMC_STATUS_BUSY))
> +		return 0;
> +	return -EAGAIN;
> +}
>  
> -	pr_warn("send_byte(0x%02x, 0x%04x) fail: 0x%02x\n", cmd, port, status);
> -	return -EIO;
> +static int send_byte(u8 cmd, u16 port)
> +{
> +	return send_byte_data(cmd, port, false);
>  }
>  
> +/*
> + * send_command - Write a command to the SMC. Callers must hold applesmc_lock.
> + * If SMC is in undefined state, any new command write resets the state machine.
> + */
> +
>  static int send_command(u8 cmd)
>  {
> -	return send_byte(cmd, APPLESMC_CMD_PORT);
> +	int ret;
> +	int i;
> +
> +	for (i = 0; i < 16; i++) {
> +		ret = send_byte(cmd, APPLESMC_CMD_PORT);
> +		if (!ret)
> +			return ret;
> +		if (ret != -EAGAIN)
> +			break;
> +		usleep_range(APPLESMC_MIN_WAIT, APPLESMC_MIN_WAIT * 16);
> +	}
> +	return -EIO;
>  }
>  
>  static int send_argument(const char *key)
> @@ -239,7 +258,8 @@ static int read_smc(u8 cmd, const char *key, u8 *buffer, u8 len)
>  	}
>  
>  	for (i = 0; i < len; i++) {
> -		if (wait_read()) {
> +		if (wait_status(SMC_STATUS_AWAITING_DATA,
> +					SMC_STATUS_AWAITING_DATA | SMC_STATUS_IB_CLOSED) < 0) {
>  			pr_warn("%.4s: read data[%d] fail\n", key, i);
>  			return -EIO;
>  		}
> @@ -250,7 +270,7 @@ static int read_smc(u8 cmd, const char *key, u8 *buffer, u8 len)
>  	for (i = 0; i < 16; i++) {
>  		udelay(APPLESMC_MIN_WAIT);
>  		status = inb(APPLESMC_CMD_PORT);
> -		if (!(status & 0x01))
> +		if (!(status & SMC_STATUS_AWAITING_DATA))
>  			break;
>  		data = inb(APPLESMC_DATA_PORT);
>  	}
> @@ -275,7 +295,7 @@ static int write_smc(u8 cmd, const char *key, const u8 *buffer, u8 len)
>  	}
>  
>  	for (i = 0; i < len; i++) {
> -		if (send_byte(buffer[i], APPLESMC_DATA_PORT)) {
> +		if (send_byte_data(buffer[i], APPLESMC_DATA_PORT, i == len - 1)) {
>  			pr_warn("%s: write data fail\n", key);
>  			return -EIO;
>  		}
>