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Date: Fri, 22 Apr 2016 12:19:57 -0300
From: Lucas De Marchi <lucas.de.marchi@...il.com>
To: Lucas De Marchi <lucas.demarchi@...el.com>,
christian.ruppert@...tech.com
Cc: "linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
"wsa@...-dreams.de" <wsa@...-dreams.de>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"mika.westerberg@...ux.intel.com" <mika.westerberg@...ux.intel.com>,
"jarkko.nikula@...ux.intel.com" <jarkko.nikula@...ux.intel.com>
Subject: Re: [PATCH] i2c: designware: do not disable adapter after transfer
CC'ing Christian.
On Fri, Apr 22, 2016 at 12:08 PM, Lucas De Marchi
<lucas.demarchi@...el.com> 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.
Christian, this is the updated patch. Now adapter starts disabled and
is disabled when there's a failed transfer. I hope this can work with
your hardware.
Leaving patch below.
Lucas De Marchi
>
> 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@...el.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
>
> #define DW_IC_ERR_TX_ABRT 0x1
>
> @@ -256,8 +257,10 @@ static void __i2c_dw_enable(struct dw_i2c_dev *dev, bool enable)
>
> do {
> dw_writel(dev, enable, DW_IC_ENABLE);
> - if ((dw_readl(dev, DW_IC_ENABLE_STATUS) & 1) == enable)
> + if ((dw_readl(dev, DW_IC_ENABLE_STATUS) & 1) == enable) {
> + dev->enabled = enable;
> return;
> + }
>
> /*
> * Wait 10 times the signaling period of the highest I2C
> @@ -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);
> + }
> + }
>
> /* if the slave address is ten bit address, enable 10BITADDR */
> ic_con = dw_readl(dev, DW_IC_CON);
> @@ -442,8 +453,8 @@ static void i2c_dw_xfer_init(struct dw_i2c_dev *dev)
> /* enforce disabled interrupts (due to HW issues) */
> i2c_dw_disable_int(dev);
>
> - /* Enable the adapter */
> - __i2c_dw_enable(dev, true);
> + if (!dev->enabled)
> + __i2c_dw_enable(dev, true);
>
> /* Clear and enable interrupts */
> dw_readl(dev, DW_IC_CLR_INTR);
> @@ -624,7 +635,8 @@ static int i2c_dw_handle_tx_abort(struct dw_i2c_dev *dev)
> }
>
> /*
> - * Prepare controller for a transaction and call i2c_dw_xfer_msg
> + * Prepare controller for a transaction and start transfer by calling
> + * i2c_dw_xfer_init()
> */
> static int
> i2c_dw_xfer(struct i2c_adapter *adap, struct i2c_msg msgs[], int num)
> @@ -671,16 +683,6 @@ i2c_dw_xfer(struct i2c_adapter *adap, struct i2c_msg msgs[], int num)
> goto done;
> }
>
> - /*
> - * We must disable the adapter before returning and signaling the end
> - * of the current transfer. 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;
> @@ -818,9 +820,19 @@ static irqreturn_t i2c_dw_isr(int this_irq, void *dev_id)
> */
>
> tx_aborted:
> - if ((stat & (DW_IC_INTR_TX_ABRT | DW_IC_INTR_STOP_DET)) || dev->msg_err)
> + if ((stat & (DW_IC_INTR_TX_ABRT | DW_IC_INTR_STOP_DET))
> + || dev->msg_err) {
> + /*
> + * We must disable interruts before returning and signaling
> + * the end of the current transfer. Otherwise the hardware
> + * might continue generating interrupts for non-existent
> + * transfers.
> + */
> + i2c_dw_disable_int(dev);
> + dw_readl(dev, DW_IC_CLR_INTR);
> +
> complete(&dev->cmd_complete);
> - else if (unlikely(dev->accessor_flags & ACCESS_INTR_MASK)) {
> + } else if (unlikely(dev->accessor_flags & ACCESS_INTR_MASK)) {
> /* workaround to trigger pending interrupt */
> stat = dw_readl(dev, DW_IC_INTR_MASK);
> i2c_dw_disable_int(dev);
> diff --git a/drivers/i2c/busses/i2c-designware-core.h b/drivers/i2c/busses/i2c-designware-core.h
> index cd409e7..115c4b0 100644
> --- a/drivers/i2c/busses/i2c-designware-core.h
> +++ b/drivers/i2c/busses/i2c-designware-core.h
> @@ -105,6 +105,7 @@ struct dw_i2c_dev {
> int (*acquire_lock)(struct dw_i2c_dev *dev);
> void (*release_lock)(struct dw_i2c_dev *dev);
> bool pm_runtime_disabled;
> + bool enabled;
> };
>
> #define ACCESS_SWAP 0x00000001
> --
> 2.5.5
>
--
Lucas De Marchi
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