lkml.org 
[lkml]   [2016]   [Apr]   [25]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH] i2c: designware: do not disable adapter after transfer
From
Date
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

...

> @@ -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

\
 
 \ /
  Last update: 2016-04-25 14:21    [W:0.059 / U:0.272 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site