From 7b1d96813317358312440d0d07abbfbeb0ef8d22 Mon Sep 17 00:00:00 2001 From: Aswath Govindraju Date: Thu, 10 Sep 2020 17:56:24 +0530 Subject: [PATCH] spi: omap2-mcspi: Improve performance waiting for CHSTAT This reverts commit 13d515c796 (spi: omap2-mcspi: Switch to readl_poll_timeout()). The amount of time spent polling for the MCSPI_CHSTAT bits to be set on AM335x-icev2 platform is less than 1us (about 0.6us) in most cases, with or without using DMA. So, in most cases the function need not sleep. Also, setting the sleep_usecs to zero would not be optimal here because ktime_add_us() used in readl_poll_timeout() is slower compared to the direct addition used after the revert. So, it is sub-optimal to use readl_poll_timeout in this case. When DMA is not enabled, this revert results in an increase of about 27% in throughput and decrease of about 20% in CPU usage. However, the CPU usage and throughput are almost the same when used with DMA. Therefore, fix this by reverting the commit which switched to using readl_poll_timeout(). Fixes: 13d515c796ad ("spi: omap2-mcspi: Switch to readl_poll_timeout()") Signed-off-by: Aswath Govindraju Link: https://lore.kernel.org/r/20200910122624.8769-1-a-govindraju@ti.com Signed-off-by: Mark Brown --- drivers/spi/spi-omap2-mcspi.c | 15 ++++++++++++--- 1 file changed, 12 insertions(+), 3 deletions(-) diff --git a/drivers/spi/spi-omap2-mcspi.c b/drivers/spi/spi-omap2-mcspi.c index 1c9478e6e5d9..d4c9510af393 100644 --- a/drivers/spi/spi-omap2-mcspi.c +++ b/drivers/spi/spi-omap2-mcspi.c @@ -24,7 +24,6 @@ #include #include #include -#include #include @@ -348,9 +347,19 @@ static void omap2_mcspi_set_fifo(const struct spi_device *spi, static int mcspi_wait_for_reg_bit(void __iomem *reg, unsigned long bit) { - u32 val; + unsigned long timeout; - return readl_poll_timeout(reg, val, val & bit, 1, MSEC_PER_SEC); + timeout = jiffies + msecs_to_jiffies(1000); + while (!(readl_relaxed(reg) & bit)) { + if (time_after(jiffies, timeout)) { + if (!(readl_relaxed(reg) & bit)) + return -ETIMEDOUT; + else + return 0; + } + cpu_relax(); + } + return 0; } static int mcspi_wait_for_completion(struct omap2_mcspi *mcspi,