[PATCH 5.4 158/408] spi: omap2-mcspi: Improve performance waiting for CHSTAT

Greg Kroah-Hartman
2020-10-27T14:36:13Z

From: Aswath Govindraju <a-govindraju@ti.com>

[ Upstream commit 7b1d96813317358312440d0d07abbfbeb0ef8d22 ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/spi/spi-omap2-mcspi.c | 17 +++++++++++++----
1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/drivers/spi/spi-omap2-mcspi.c b/drivers/spi/spi-omap2-mcspi.c
index 4433cb4de564e..7646b4b56bed9 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>
#include <linux/gpio.h>
@@ -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;
-
- 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,
--
2.25.1