linux-kernel - Re: [PATCH v1] i2c: designware: Disable TX_EMPTY irq while waiting for block length byte

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Message-ID: <4999b3d9-e299-6c0b-0a08-11b33d06a636@amperemail.onmicrosoft.com>
Date:   Mon, 16 Oct 2023 09:52:17 +0700
From:   Tam Chi Nguyen <tamnguyenchi@...eremail.onmicrosoft.com>
To:     Yann Sionneau <ysionneau@...rayinc.com>,
        Tam Nguyen <tamnguyenchi@...amperecomputing.com>,
        linux-kernel@...r.kernel.org, linux-i2c@...r.kernel.org
Cc:     patches@...erecomputing.com, jarkko.nikula@...ux.intel.com,
        andriy.shevchenko@...ux.intel.com, mika.westerberg@...ux.intel.com,
        jsd@...ihalf.com, chuong@...amperecomputing.com,
        darren@...amperecomputing.com, stable@...r.kernel.org
Subject: Re: [PATCH v1] i2c: designware: Disable TX_EMPTY irq while waiting
 for block length byte


On 10/3/2023 15:11, Yann Sionneau wrote:
> 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@...r.kernel.org
>> Signed-off-by: Chuong Tran <chuong@...amperecomputing.com>
>> Signed-off-by: Tam Nguyen <tamnguyenchi@...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.
>
Thank you for your time to test this patch.

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