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Date:   Mon, 16 Oct 2023 09:47:06 +0700
From:   Tam Chi Nguyen <tamnguyenchi@...eremail.onmicrosoft.com>
To:     Serge Semin <fancer.lancer@...il.com>,
        Tam Nguyen <tamnguyenchi@...amperecomputing.com>
Cc:     linux-kernel@...r.kernel.org, linux-i2c@...r.kernel.org,
        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 9/29/2023 23:08, Serge Semin wrote:
> On Fri, Sep 29, 2023 at 10:53:56AM +0700, 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;
> Is it possible to reduce the indentations level? Like this:
>
> 		/*
> 		 * Because we don't know the buffer length in the
> 		 * I2C_FUNC_SMBUS_BLOCK_DATA case, we can't stop the
> 		 * transaction here. Also disable the TX_EMPTY IRQ
> 		 * while waiting for the data length byte to avoid the
> 		 * bogus interrupts flood.
> 		 */
> 		if (flags & I2C_M_RECV_LEN) {
>    			dev->status |= STATUS_WRITE_IN_PROGRESS;
> 			intr_mask &= ~DW_IC_INTR_TX_EMPTY;
> 			break;
> 		} else if (buf_len > 0) {
>    			/* more bytes to be written */
>    			dev->status |= STATUS_WRITE_IN_PROGRESS;
> 			break;
> 		} else {
> 			dev->status &= ~STATUS_WRITE_IN_PROGRESS;
> 		}
Thank you very much for your advice. I will update in V2.
>>   			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);
> 1. What about just:
> 	regmap_update_bits(dev->map, DW_IC_INTR_MASK, DW_IC_INTR_TX_EMPTY,
> 			   DW_IC_INTR_TX_EMPTY);
Right, much better with this update. I'll update it in v2.
> 2. The in-situ comment is pointless because the statement already
> implies the IRQ re-enabling. I suggest to add more details of _why_
> the IRQ needs to be re-enabled (what is supposed to be done after it's
> re-enabled?).

Got that. I will add more context here. Thank for the advice.

Best regards,
Tam Nguyen

> -Serge(y)
>
>> +
>>   	return len;
>>   }
>>   
>> -- 
>> 2.25.1
>>

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