[rtc-linux] [RFC] ARM i.MX: rtc: change interrupt handling for DryIce

[Andrew Morton]

On Thu, 31 Jan 2013 15:16:17 +0100
Steffen Trumtrar <s.trumtrar at pengutronix.de> wrote:

> di_write_wait uses a very short timeout of 1ms for the wait_queue.
> This may lead to write errors to some registers. Write errors to DCAMR and
> DSR_CAF where the only one observed, though:
> 
> Tue Jan 14 15:32:23 2014  -0.985304 seconds
> Tue Jan 14 15:32:24 2014  -0.985236 seconds
> Tue Jan 14 15:32:25 2014  -0.986601 seconds
> imxdi_rtc 53ffc000.dryice: Write-wait timeout val = 0x52d5588a reg = 0x00000008
> Tue Jan 14 15:32:26 2014  -0.983772 seconds
> Tue Jan 14 15:32:27 2014  -0.983594 seconds
> imxdi_rtc 53ffc000.dryice: Write-wait timeout val = 0x52d5588c reg = 0x00000008
> Tue Jan 14 15:32:28 2014  -0.983596 seconds
> imxdi_rtc 53ffc000.dryice: Write-wait timeout val = 0x52d5588d reg = 0x00000008
> Tue Jan 14 15:32:29 2014  -0.983300 seconds
> Tue Jan 14 15:32:30 2014  -0.982809 seconds
> 
> Just increasing this timeout leads to a race condition in the interrupt handler.
> After a couple minutes of running
> 	while true; do hwclock; done
> the interrupt isn't handled by the driver and disabled in the process.
> This seems to be because of the waitqueue check and then returning out of the
> handler, as there is no other handler that takes over.
> 
> Use wait_event_interruptible without a timeout instead and do not leave the
> interrupt handler in case of an empty waitqueue, but handle the actual irq case.
> As before, nothing is done in that case though.
> 

The patch makes changes which aren't described in the above changelog:

- Fiddles with the new DIER_SVIE

- Enables the DIER_WEIE interrupt

> @@ -168,15 +169,18 @@ static int di_write_wait(struct imxdi_dev *imxdi, u32 val, int reg)
>  	__raw_writel(val, imxdi->ioaddr + reg);
>  
>  	/* wait for the write to finish */
> -	ret = wait_event_interruptible_timeout(imxdi->write_wait,
> -			imxdi->dsr & (DSR_WCF | DSR_WEF), msecs_to_jiffies(1));
> -	if (ret < 0) {
> +	ret = wait_event_interruptible(imxdi->write_wait, imxdi->dsr &
> +					(DSR_WCF | DSR_WEF));
> +
> +	if (ret <= 0) {
>  		rc = ret;
>  		goto out;
> -	} else if (ret == 0) {
> +	} else if (ret > 0) {
>  		dev_warn(&imxdi->pdev->dev,
>  				"Write-wait timeout "
>  				"val = 0x%08x reg = 0x%08x\n", val, reg);
> +		rc = -ERESTARTSYS;
> +		goto out;
>  	}

This code looks all confused.  wait_event_interruptible() can only
return two things: zero or -ERESTARTSYS.  That code which handles (ret
> 0) will never be executed.

di_write_wait() should return -ERESTARTSYS if
wait_event_interruptible() returned -ERESTARTSYS and it should return 0
if wait_event_interruptible() returned 0.  So local variable `ret' can
just go away.  Although I'd suggest then renaming `rc' to `ret', as the
latter is more conventional.