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Subject[PATCH] i2c: designware: use enable on resume instead initialization
From: Fabio Mello <>

According to documentation and tests, initialization is not
necessary on module resume, since the controller keeps its state
between disable/enable. Change the target address is also allowed.

So, this patch replaces the initialization on module resume with a
simple enable, and removes the (non required anymore) enables and

Signed-off-by: Fabio Mello <>
Signed-off-by: Lucas De Marchi <>

These pictures explain a little more the consequence of letting the
enable+disable in the code:

The yellow line is a GPIO toggle in userspace to mark when we start and finish
the i2c transactions. The blue line is the SCL in that i2c bus. Take a look on
the huge pauses we have between any 2 transactions. These pauses are removed
with this patch and we are able to read our sensor's values in 950usec rather
than 5.24msec we had before. We are testing this using a Minnowboard Max that
has a designware i2c controller.

There's this comment in the code suggesting the designware controller might
have problems if we don't disable it after each transfer. We left a stress
code running for 3 days to check if anything bad would happen. This is the
test code using a PCA9685 (just because it was the easiest device we had
available to check read+write commands):

drivers/i2c/busses/i2c-designware-core.c | 19 ++++---------------
drivers/i2c/busses/i2c-designware-platdrv.c | 2 +-
2 files changed, 5 insertions(+), 16 deletions(-)

diff --git a/drivers/i2c/busses/i2c-designware-core.c b/drivers/i2c/busses/i2c-designware-core.c
index 6e25c01..b386c10 100644
--- a/drivers/i2c/busses/i2c-designware-core.c
+++ b/drivers/i2c/busses/i2c-designware-core.c
@@ -375,8 +375,12 @@ int i2c_dw_init(struct dw_i2c_dev *dev)
/* configure the i2c master */
dw_writel(dev, dev->master_cfg , DW_IC_CON);

+ /* Enable the adapter */
+ __i2c_dw_enable(dev, true);
if (dev->release_lock)
return 0;
@@ -405,9 +409,6 @@ static void i2c_dw_xfer_init(struct dw_i2c_dev *dev)
struct i2c_msg *msgs = dev->msgs;
u32 ic_con, ic_tar = 0;

- /* Disable the adapter */
- __i2c_dw_enable(dev, false);
/* if the slave address is ten bit address, enable 10BITADDR */
ic_con = dw_readl(dev, DW_IC_CON);
if (msgs[dev->msg_write_idx].flags & I2C_M_TEN) {
@@ -434,9 +435,6 @@ static void i2c_dw_xfer_init(struct dw_i2c_dev *dev)
/* enforce disabled interrupts (due to HW issues) */

- /* Enable the adapter */
- __i2c_dw_enable(dev, true);
/* Clear and enable interrupts */
@@ -665,15 +663,6 @@ i2c_dw_xfer(struct i2c_adapter *adap, struct i2c_msg msgs[], int num)
goto done;

- /*
- * We must disable the adapter before unlocking the &dev->lock mutex
- * below. Otherwise the hardware might continue generating interrupts
- * which in turn causes a race condition with the following transfer.
- * Needs some more investigation if the additional interrupts are
- * a hardware bug or this driver doesn't handle them correctly yet.
- */
- __i2c_dw_enable(dev, false);
if (dev->msg_err) {
ret = dev->msg_err;
goto done;
diff --git a/drivers/i2c/busses/i2c-designware-platdrv.c b/drivers/i2c/busses/i2c-designware-platdrv.c
index c270f5f..0598695 100644
--- a/drivers/i2c/busses/i2c-designware-platdrv.c
+++ b/drivers/i2c/busses/i2c-designware-platdrv.c
@@ -320,7 +320,7 @@ static int dw_i2c_resume(struct device *dev)

if (!i_dev->pm_runtime_disabled)
- i2c_dw_init(i_dev);
+ i2c_dw_enable(i_dev);

return 0;

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