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| author | Aswath Govindraju <a-govindraju@ti.com> | 2020-09-10 17:56:24 +0530 |
|---|---|---|
| committer | Mark Brown <broonie@kernel.org> | 2020-09-22 01:04:20 +0100 |
| commit | 7b1d96813317358312440d0d07abbfbeb0ef8d22 (patch) | |
| tree | 2a539c1e9bda656c43231becb255a1aab9c03358 /drivers/spi/spi-omap2-mcspi.c | |
| parent | 4c3a14fbc05a09fc369fb68a86cdbf6f441a29f2 (diff) | |
| download | lwn-7b1d96813317358312440d0d07abbfbeb0ef8d22.tar.gz lwn-7b1d96813317358312440d0d07abbfbeb0ef8d22.zip | |
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 <a-govindraju@ti.com>
Link: https://lore.kernel.org/r/20200910122624.8769-1-a-govindraju@ti.com
Signed-off-by: Mark Brown <broonie@kernel.org>
Diffstat (limited to 'drivers/spi/spi-omap2-mcspi.c')
| -rw-r--r-- | drivers/spi/spi-omap2-mcspi.c | 17 |
1 files changed, 13 insertions, 4 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 <linux/of.h> #include <linux/of_device.h> #include <linux/gcd.h> -#include <linux/iopoll.h> #include <linux/spi/spi.h> @@ -348,9 +347,19 @@ disable_fifo: static int mcspi_wait_for_reg_bit(void __iomem *reg, unsigned long bit) { - u32 val; - - return readl_poll_timeout(reg, val, val & bit, 1, MSEC_PER_SEC); + unsigned long timeout; + + 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, |