| Message ID | 20200910122624.8769-1-a-govindraju@ti.com (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | 7b1d96813317358312440d0d07abbfbeb0ef8d22 |
| Headers | show |
| Series | Revert "spi: omap2-mcspi: Switch to readl_poll_timeout()" | expand |
On Thu, Sep 10, 2020 at 05:56:24PM +0530, Aswath Govindraju wrote: > This reverts commit 13d515c796adc49a49b0cd2212ccd7f43a37fc5a. > > 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 Please submit patches using subject lines reflecting the style for the subsystem, this makes it easier for people to identify relevant patches. Look at what existing commits in the area you're changing are doing and make sure your subject lines visually resemble what they're doing. There's no need to resubmit to fix this alone.
On Mon, Sep 21, 2020 at 07:56:38PM +0100, Mark Brown wrote: > On Thu, Sep 10, 2020 at 05:56:24PM +0530, Aswath Govindraju wrote: > > This reverts commit 13d515c796adc49a49b0cd2212ccd7f43a37fc5a. > > > > 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 > > Please submit patches using subject lines reflecting the style for the > subsystem, this makes it easier for people to identify relevant patches. > Look at what existing commits in the area you're changing are doing and > make sure your subject lines visually resemble what they're doing. > There's no need to resubmit to fix this alone. Oh, and also: Please include human readable descriptions of things like commits and issues being discussed in e-mail in your mails, this makes them much easier for humans to read especially when they have no internet access. I do frequently catch up on my mail on flights or while otherwise travelling so this is even more pressing for me than just being about making things a bit easier to read.
On Thu, 10 Sep 2020 17:56:24 +0530, Aswath Govindraju wrote: > This reverts commit 13d515c796adc49a49b0cd2212ccd7f43a37fc5a. > > 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. > > [...] Applied to https://git.kernel.org/pub/scm/linux/kernel/git/broonie/spi.git for-next Thanks! [1/1] spi: omap2-mcspi: Improve performance waiting for CHSTAT commit: 7b1d96813317358312440d0d07abbfbeb0ef8d22 All being well this means that it will be integrated into the linux-next tree (usually sometime in the next 24 hours) and sent to Linus during the next merge window (or sooner if it is a bug fix), however if problems are discovered then the patch may be dropped or reverted. You may get further e-mails resulting from automated or manual testing and review of the tree, please engage with people reporting problems and send followup patches addressing any issues that are reported if needed. If any updates are required or you are submitting further changes they should be sent as incremental updates against current git, existing patches will not be replaced. Please add any relevant lists and maintainers to the CCs when replying to this mail. Thanks, Mark
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 @@ 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,
This reverts commit 13d515c796adc49a49b0cd2212ccd7f43a37fc5a. 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> --- drivers/spi/spi-omap2-mcspi.c | 17 +++++++++++++---- 1 file changed, 13 insertions(+), 4 deletions(-) base-commit: dff9f829e5b0181d4ed9d35aa62d695292399b54