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SubjectRe: [PATCH v1] i2c: designware: Disable TX_EMPTY irq while waiting for block length byte
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Hi Tam,

On 9/29/23 05:53, Tam Nguyen wrote:
> During SMBus block data read process, we have seen high interrupt rate
> because of TX_EMPTY irq status while waiting for block length byte (the
> first data byte after the address phase). The interrupt handler does not
> do anything because the internal state is kept as STATUS_WRITE_IN_PROGRESS.
> Hence, we should disable TX_EMPTY irq until I2C DW receives first data
> byte from I2C device, then re-enable it.
>
> It takes 0.789 ms for host to receive data length from slave.
> Without the patch, i2c_dw_isr is called 99 times by TX_EMPTY interrupt.
> And it is none after applying the patch.
>
> Cc: stable@vger.kernel.org
> Signed-off-by: Chuong Tran <chuong@os.amperecomputing.com>
> Signed-off-by: Tam Nguyen <tamnguyenchi@os.amperecomputing.com>
> ---
> drivers/i2c/busses/i2c-designware-master.c | 13 +++++++++++++
> 1 file changed, 13 insertions(+)
>
> diff --git a/drivers/i2c/busses/i2c-designware-master.c b/drivers/i2c/busses/i2c-designware-master.c
> index 55ea91a63382..2152b1f9b27c 100644
> --- a/drivers/i2c/busses/i2c-designware-master.c
> +++ b/drivers/i2c/busses/i2c-designware-master.c
> @@ -462,6 +462,13 @@ i2c_dw_xfer_msg(struct dw_i2c_dev *dev)
> if (buf_len > 0 || flags & I2C_M_RECV_LEN) {
> /* more bytes to be written */
> dev->status |= STATUS_WRITE_IN_PROGRESS;
> + /*
> + * In I2C_FUNC_SMBUS_BLOCK_DATA case, there is no data
> + * to send before receiving data length from slave.
> + * Disable TX_EMPTY while waiting for data length byte
> + */
> + if (flags & I2C_M_RECV_LEN)
> + intr_mask &= ~DW_IC_INTR_TX_EMPTY;
> break;
> } else
> dev->status &= ~STATUS_WRITE_IN_PROGRESS;
> @@ -485,6 +492,7 @@ i2c_dw_recv_len(struct dw_i2c_dev *dev, u8 len)
> {
> struct i2c_msg *msgs = dev->msgs;
> u32 flags = msgs[dev->msg_read_idx].flags;
> + u32 intr_mask;
>
> /*
> * Adjust the buffer length and mask the flag
> @@ -495,6 +503,11 @@ i2c_dw_recv_len(struct dw_i2c_dev *dev, u8 len)
> msgs[dev->msg_read_idx].len = len;
> msgs[dev->msg_read_idx].flags &= ~I2C_M_RECV_LEN;
>
> + /* Re-enable TX_EMPTY interrupt. */
> + regmap_read(dev->map, DW_IC_INTR_MASK, &intr_mask);
> + intr_mask |= DW_IC_INTR_TX_EMPTY;
> + regmap_write(dev->map, DW_IC_INTR_MASK, intr_mask);
> +
> return len;
> }

I tested this patch on Kalray k200 and k200lp boards (Coolidge SoC, kvx
arch). With this patch all our CI pipelines are green.

Tested-by: Yann Sionneau <ysionneau@kalrayinc.com>

--

Yann





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