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SubjectRe: [PATCH v4 1/4] i2c: designware: wait for disable/enable only if necessary
On Tue, Aug 23, 2016 at 07:18:53PM -0300, Lucas De Marchi wrote:
> From: José Roberto de Souza <jose.souza@intel.com>
>
> If we aren't going to continue using the controller we can just disable
> it instead of waiting for it to complete. The biggest improvement here
> is when a I2C transaction is completed and it doesn't block until
> the adapter is disabled. When a new transfer is needed we will disable
> and wait for its completion.
>
> This way the adapter will continue changing its state in parallel to the
> execution of the thread that requested the I2C transaction saving most
> of the time 25~250 usec per I2C transaction.
>
> A simple program doing a register read (1 byte write, 1 byte read)
> alternating on 2 different slaves repeated 25k times for each and
> measurements taken 4 times we get:
>
> perf stat -r4 chrt -f 10 ./i2c-test /dev/i2c-1 25000 0x40 0x6 0x1e 0x00
>
> Before:
> 30.879317977 seconds time elapsed ( +- 14.83% )
> After:
> 8.638705161 seconds time elapsed ( +- 5.90% )
>
> Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
> Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
> ---
> drivers/i2c/busses/i2c-designware-core.c | 13 +++++++++----
> 1 file changed, 9 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/i2c/busses/i2c-designware-core.c b/drivers/i2c/busses/i2c-designware-core.c
> index 99b54be..2c61585 100644
> --- a/drivers/i2c/busses/i2c-designware-core.c
> +++ b/drivers/i2c/busses/i2c-designware-core.c
> @@ -252,10 +252,15 @@ static u32 i2c_dw_scl_lcnt(u32 ic_clk, u32 tLOW, u32 tf, int offset)
>
> static void __i2c_dw_enable(struct dw_i2c_dev *dev, bool enable)
> {
> + dw_writel(dev, enable, DW_IC_ENABLE);
> +}
> +
> +static void __i2c_dw_enable_and_wait(struct dw_i2c_dev *dev, bool enable)
> +{
> int timeout = 100;
>
> do {
> - dw_writel(dev, enable, DW_IC_ENABLE);
> + __i2c_dw_enable(dev, enable);
> if ((dw_readl(dev, DW_IC_ENABLE_STATUS) & 1) == enable)
> return;
>
> @@ -321,7 +326,7 @@ int i2c_dw_init(struct dw_i2c_dev *dev)
> }
>
> /* Disable the adapter */
> - __i2c_dw_enable(dev, false);
> + __i2c_dw_enable_and_wait(dev, false);
>
> /* set standard and fast speed deviders for high/low periods */
>
> @@ -414,7 +419,7 @@ static void i2c_dw_xfer_init(struct dw_i2c_dev *dev)
> u32 ic_con, ic_tar = 0;
>
> /* Disable the adapter */
> - __i2c_dw_enable(dev, false);
> + __i2c_dw_enable_and_wait(dev, false);
>
> /* if the slave address is ten bit address, enable 10BITADDR */
> ic_con = dw_readl(dev, DW_IC_CON);
> @@ -833,7 +838,7 @@ tx_aborted:
> void i2c_dw_disable(struct dw_i2c_dev *dev)
> {
> /* Disable controller */
> - __i2c_dw_enable(dev, false);
> + __i2c_dw_enable_and_wait(dev, false);
>
> /* Disable all interupts */
> dw_writel(dev, 0, DW_IC_INTR_MASK);
> --
> 2.7.4
>

Regression reported: https://bugzilla.kernel.org/show_bug.cgi?id=194969

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