On 04/22/2016 06:08 PM, Lucas De Marchi wrote:
Disabling the adapter after each transfer is pretty bad for sensors and
other devices doing small transfers at a high rate. It slows down the
transfer rate a lot since each of them have to wait the adapter to be
enabled again.
During the transfer init we check the status register for no activity
and TX buffer being empty since otherwise we can't change IC_TAR
dynamically.
When a transfer fails the adapter will still be disabled - this is a
conservative approach. When transfers succeed, the adapter is left
enabled and it's configured so to disable interrupts.
With a small program test to read/write registers in a sensor the speed
doubled. Example below with write sequences of 16 bytes:
Before:
i2c-transfer-time -w -a 0x40 -x 6 -n 20000 -- 0 0 0xd0 0x07 0 0 0xd0 0x07 0 0 0xd0 0x07 0 0 0xd0 0x07
num_transfers=20000
transfer_time_avg=1032.728500us
After:
i2c-transfer-time -w -a 0x40 -x 6 -n 20000 -- 0 0 0xd0 0x07 0 0 0xd0 0x07 0 0 0xd0 0x07 0 0 0xd0 0x07
num_transfers=20000
transfer_time_avg=470.256050us
Signed-off-by: Lucas De Marchi <lucas.demarchi@xxxxxxxxx>
---
drivers/i2c/busses/i2c-designware-core.c | 48 ++++++++++++++++++++------------
drivers/i2c/busses/i2c-designware-core.h | 1 +
2 files changed, 31 insertions(+), 18 deletions(-)
diff --git a/drivers/i2c/busses/i2c-designware-core.c b/drivers/i2c/busses/i2c-designware-core.c
index 99b54be..8a08e68 100644
--- a/drivers/i2c/busses/i2c-designware-core.c
+++ b/drivers/i2c/busses/i2c-designware-core.c
@@ -90,6 +90,7 @@
DW_IC_INTR_STOP_DET)
#define DW_IC_STATUS_ACTIVITY 0x1
+#define DW_IC_STATUS_TX_EMPTY 0x2
...
@@ -413,8 +416,16 @@ 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 (dev->enabled) {
+ u32 ic_status;
+
+ /* check ic_tar and ic_con can be dynamically updated */
+ ic_status = dw_readl(dev, DW_IC_STATUS);
+ if (ic_status & DW_IC_STATUS_ACTIVITY
+ || !(ic_status & DW_IC_STATUS_TX_EMPTY)) {
+ __i2c_dw_enable(dev, false);
+ }
+ }
Worth to double check this. I see bit 1 means TX FIFO not full and bit 2
is TX FIFO completely empty.
Otherwise I'm fine with the patch as long as it works for Christian.
--
Jarkko
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