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));
>
