From d46a24a9d2dbe1a14988877e9e602d027cd35d43 Mon Sep 17 00:00:00 2001 From: Ulf Hansson Date: Tue, 4 Feb 2020 09:54:38 +0100 Subject: [PATCH] mmc: core: Throttle polling rate for CMD6 MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit In mmc_poll_for_busy() we loop continuously, either by sending a CMD13 or by invoking the ->card_busy() host ops, as to detect when the card stops signaling busy. This behaviour is problematic as it may cause CPU hogging, especially when the busy signal time reaches beyond a few ms. Let's fix the issue by adding a throttling mechanism, that inserts a usleep_range() in between the polling attempts. The sleep range starts at 32-64us, but increases for each loop by a factor of 2, up until the range reaches ~32-64ms. In this way, we are able to keep the loop fine-grained enough for short busy signaling times, while also not hogging the CPU for longer times. Note that, this change is inspired by the similar throttling mechanism that we already use for mmc_do_erase(). Reported-by: Michał Mirosław Signed-off-by: Ulf Hansson Tested-by: Baolin Wang Tested-by: Ludovic Barre Reviewed-by: Ludovic Barre Link: https://lore.kernel.org/r/20200204085449.32585-2-ulf.hansson@linaro.org --- drivers/mmc/core/mmc_ops.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/drivers/mmc/core/mmc_ops.c b/drivers/mmc/core/mmc_ops.c index e025604..da424dc 100644 --- a/drivers/mmc/core/mmc_ops.c +++ b/drivers/mmc/core/mmc_ops.c @@ -456,6 +456,7 @@ static int mmc_poll_for_busy(struct mmc_card *card, unsigned int timeout_ms, struct mmc_host *host = card->host; int err; unsigned long timeout; + unsigned int udelay = 32, udelay_max = 32768; u32 status = 0; bool expired = false; bool busy = false; @@ -500,6 +501,13 @@ static int mmc_poll_for_busy(struct mmc_card *card, unsigned int timeout_ms, mmc_hostname(host), __func__); return -ETIMEDOUT; } + + /* Throttle the polling rate to avoid hogging the CPU. */ + if (busy) { + usleep_range(udelay, udelay * 2); + if (udelay < udelay_max) + udelay *= 2; + } } while (busy); return 0; -- 2.7.4