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Date: Thu, 5 Nov 2020 08:12:28 -0800
From: Guenter Roeck <linux@...ck-us.net>
To: Brad Campbell <brad@...rfbargle.com>,
Andreas Kemnade <andreas@...nade.info>,
Jean Delvare <jdelvare@...e.com>
Cc: Arnd Bergmann <arnd@...db.de>, rydberg@...math.org,
linux-hwmon@...r.kernel.org,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
hns@...delico.com
Subject: Re: [PATCH] applesmc: Re-work SMC comms v2
On 11/4/20 11:26 PM, Brad Campbell wrote:
> 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.
>
Still a few formatting problems, but I like this version. Id take
care of the formatting myself, but send_command() will need a change.
Subject should be
[PATCH v<version>] hwmon: (applesmc) ...
> v2 : Address logic and coding style
Change log should be after '---'
>
> Reported-by: Andreas Kemnade <andreas@...nade.info>
> Fixes: fff2d0f701e6 ("hwmon: (applesmc) avoid overlong udelay()")
> Signed-off-by: Brad Campbell <brad@...rfbargle.com>
>
> ---
> diff --git a/drivers/hwmon/applesmc.c b/drivers/hwmon/applesmc.c
> index a18887990f4a..de890f3ec12f 100644
> --- a/drivers/hwmon/applesmc.c
> +++ b/drivers/hwmon/applesmc.c
> @@ -42,6 +42,11 @@
>
> #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 */
> +
Hah, tricked you here ;-). Using "BIT()" requires
#include <linux/bits.h>
> /* wait up to 128 ms for a status change. */
> #define APPLESMC_MIN_WAIT 0x0010
> #define APPLESMC_RETRY_WAIT 0x0100
> @@ -151,65 +156,69 @@ 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
> */
> -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)
> + if ((status & mask) == val)
> return 0;
> /* timeout: give up */
> if (time_after(jiffies, end))
> break;
> - }
> -
> - pr_warn("wait_read() fail: 0x%02x\n", status);
> + usleep_range(us, us * 16);
> + }
Bad indentation of "}"
> 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 ret;
>
> + ret = wait_status(SMC_STATUS_BUSY, SMC_STATUS_BUSY | SMC_STATUS_IB_CLOSED);
> + if (ret)
> + return ret;
> 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);
> - }
> + return wait_status(skip ? 0 : SMC_STATUS_BUSY, SMC_STATUS_BUSY);
> +}
>
> - 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);
> + u8 status;
> + int ret;
> +
> + ret = wait_status(0, SMC_STATUS_IB_CLOSED);
> + if (ret)
> + return ret;
> +
> + status = inb(APPLESMC_CMD_PORT);
> +
Is this read necessary ? 'status' isn't used subsequently, meaning we'll
probably get static analyzer warnings about a variable which is assigned
but unused. If the read is necessary, just don't assign it to a variable.
> + outb(cmd, APPLESMC_CMD_PORT);
> + return wait_status(SMC_STATUS_BUSY, SMC_STATUS_BUSY);
> }
>
> static int send_argument(const char *key)
> @@ -239,7 +248,9 @@ 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_BUSY,
> + SMC_STATUS_AWAITING_DATA | SMC_STATUS_BUSY |
> + SMC_STATUS_IB_CLOSED)) {
> pr_warn("%.4s: read data[%d] fail\n", key, i);
> return -EIO;
> }
> @@ -250,7 +261,7 @@ 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 +286,7 @@ 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;
> }
>
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