On Thu, Nov 05, 2020 at 04:47:25PM +1100, Brad Campbell wrote:
> Commit fff2d0f701e6 ("hwmon: (applesmc) avoid overlong udelay()") introduced
> an issue whereby communication with the SMC became unreliable with write
> errors :
>
> [ 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.
>
> Reported-by: Andreas Kemnade
Add
Fixes: fff2d0f701e6 ("hwmon: (applesmc) avoid overlong udelay()")
> Signed-off-by: Brad Campbell
>
> ---
> diff --git a/drivers/hwmon/applesmc.c b/drivers/hwmon/applesmc.c
> index a18887990f4a..22cc5122ce9a 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 from VirtualSMC */
> +#define SMC_STATUS_AWAITING_DATA 0x01 ///< Data waiting to be read
> +#define SMC_STATUS_IB_CLOSED 0x02 /// A write is pending / will ignore
> input
> +#define SMC_STATUS_BUSY 0x04 ///< Busy in the middle of a command.
> +
Maybe consider using BIT() while at it.
/* Please use standard comments */
Also, what does the "<" mean ? Is that supposed to be negated
(ie bit set means not busy) ? If so, that isn't a standard notation
that I am aware of. Maybe "not set if busy in the middle of a command"
would be better in this case.
> /* wait up to 128 ms for a status change. */
> #define APPLESMC_MIN_WAIT0x0010
> #define APPLESMC_RETRY_WAIT 0x0100
> @@ -151,65 +156,77 @@ 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);
> + }
> + pr_warn("wait_status timeout: 0x%02x, 0x%02x, 0x%02x\n", status, val,
> mask);
> 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)
I would suggest to keep send_byte() and change it to the following.
static int send_byte(u8 cmd, u16 port)
{
return send_byte_data(cmd, port, false);
}
That would limit the number of changes needed later in the code
(it is never called with a hard 'true' as parameter).
> +
> +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;
> + u8 wstat = SMC_STATUS_BUSY;
>
> + if (skip)
> + wstat = 0;
u8 wstat = skip ? 0 : SMC_STATUS_BUSY;
> + if (wait_status(SMC_STATUS_BUSY,
> + SMC_STATUS_BUSY | SMC_STATUS_IB_CLOSED))
This fits one line, and the error code
should really not be overwritten.
ret = wait_status(SMC_STATUS_BUSY, SMC_STATUS_BUSY |
SMC_STATUS_IB_CLOSED);
if (ret)
return ret;
> + goto fail;
> 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);
> - }
> -
> -
