Re: [PATCH] mmc: cqhci: Avoid false "cqhci: CQE stuck on" by not open-coding timeout loop

[Adrian Hunter]

On 14/04/20 2:27 am, Douglas Anderson wrote:
> Open-coding a timeout loop invariably leads to errors with handling
> the timeout properly in one corner case or another.  In the case of
> cqhci we might report "CQE stuck on" even if it wasn't stuck on.
> You'd just need this sequence of events to happen in cqhci_off():
> 
> 1. Call ktime_get().
> 2. Something happens to interrupt the CPU for > 100 us (context switch
>    or interrupt).
> 3. Check time and; set "timed_out" to true since > 100 us.
> 4. Read CQHCI_CTL.
> 5. Both "reg & CQHCI_HALT" and "timed_out" are true, so break.
> 6. Since "timed_out" is true, falsely print the error message.
> 
> Rather than fixing the polling loop, use readx_poll_timeout() like
> many people do.  This has been time tested to handle the corner cases.
> 
> Fixes: a4080225f51d ("mmc: cqhci: support for command queue enabled host")
> Signed-off-by: Douglas Anderson <dianders@xxxxxxxxxxxx>

Acked-by: Adrian Hunter <adrian.hunter@xxxxxxxxx>


> ---
> 
>  drivers/mmc/host/cqhci.c | 21 ++++++++++-----------
>  1 file changed, 10 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/mmc/host/cqhci.c b/drivers/mmc/host/cqhci.c
> index c2239ee2c0ef..75934f3c117e 100644
> --- a/drivers/mmc/host/cqhci.c
> +++ b/drivers/mmc/host/cqhci.c
> @@ -5,6 +5,7 @@
>  #include <linux/delay.h>
>  #include <linux/highmem.h>
>  #include <linux/io.h>
> +#include <linux/iopoll.h>
>  #include <linux/module.h>
>  #include <linux/dma-mapping.h>
>  #include <linux/slab.h>
> @@ -349,12 +350,16 @@ static int cqhci_enable(struct mmc_host *mmc, struct mmc_card *card)
>  /* CQHCI is idle and should halt immediately, so set a small timeout */
>  #define CQHCI_OFF_TIMEOUT 100
>  
> +static u32 cqhci_read_ctl(struct cqhci_host *cq_host)
> +{
> +	return cqhci_readl(cq_host, CQHCI_CTL);
> +}
> +
>  static void cqhci_off(struct mmc_host *mmc)
>  {
>  	struct cqhci_host *cq_host = mmc->cqe_private;
> -	ktime_t timeout;
> -	bool timed_out;
>  	u32 reg;
> +	int err;
>  
>  	if (!cq_host->enabled || !mmc->cqe_on || cq_host->recovery_halt)
>  		return;
> @@ -364,15 +369,9 @@ static void cqhci_off(struct mmc_host *mmc)
>  
>  	cqhci_writel(cq_host, CQHCI_HALT, CQHCI_CTL);
>  
> -	timeout = ktime_add_us(ktime_get(), CQHCI_OFF_TIMEOUT);
> -	while (1) {
> -		timed_out = ktime_compare(ktime_get(), timeout) > 0;
> -		reg = cqhci_readl(cq_host, CQHCI_CTL);
> -		if ((reg & CQHCI_HALT) || timed_out)
> -			break;
> -	}
> -
> -	if (timed_out)
> +	err = readx_poll_timeout(cqhci_read_ctl, cq_host, reg,
> +				 reg & CQHCI_HALT, 0, CQHCI_OFF_TIMEOUT);
> +	if (err < 0)
>  		pr_err("%s: cqhci: CQE stuck on\n", mmc_hostname(mmc));
>  	else
>  		pr_debug("%s: cqhci: CQE off\n", mmc_hostname(mmc));
>