Messages in this thread | | | Subject | Re: [PATCH] i2c: designware: do not disable adapter after transfer | From | Jarkko Nikula <> | Date | Mon, 25 Apr 2016 14:51:22 +0300 |
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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@intel.com> > --- > 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
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> @@ -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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