linux-kernel - Re: [PATCH v2] i2c: designware: Disable TX_EMPTY irq while waiting for block length byte

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Message-ID: <673zmmjr4bpsfepbcjegmj7gddvj3yeacljmiux57ywn42fk4p@behzguqduv6k>
Date:   Fri, 3 Nov 2023 16:02:15 +0300
From:   Serge Semin <fancer.lancer@...il.com>
To:     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 v2] i2c: designware: Disable TX_EMPTY irq while waiting
 for block length byte

On Thu, Nov 02, 2023 at 10:30:08AM +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 DesignWare receives
> first data byte from I2C device, then re-enable it to resume SMBus
> transaction.
> 
> 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
> Co-developed-by: Chuong Tran <chuong@...amperecomputing.com>
> Signed-off-by: Chuong Tran <chuong@...amperecomputing.com>
> Signed-off-by: Tam Nguyen <tamnguyenchi@...amperecomputing.com>

Thanks!
Reviewed-by: Serge Semin <fancer.lancer@...il.com>

-Serge(y)

> ---
> v2:
> 	+ Reduce the indentations level
> 	+ Use regmap_update_bits for bitfield update
> 	+ Rewrite comment statement                     [Serge]
> 	+ Update commit message
> 	+ Add Co-developed-by tag for co-authors        [Andy]
> 
> v1:
>   https://lore.kernel.org/lkml/avd7jhwexehgbvi6euzdwvf5zvqqgjx4ozo6uxu2qpmlarvva3@sgkce3rvovwk/T/
> ---
>  drivers/i2c/busses/i2c-designware-master.c | 19 ++++++++++++++++---
>  1 file changed, 16 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-designware-master.c b/drivers/i2c/busses/i2c-designware-master.c
> index 55ea91a63382..ae76620ef35e 100644
> --- a/drivers/i2c/busses/i2c-designware-master.c
> +++ b/drivers/i2c/busses/i2c-designware-master.c
> @@ -456,10 +456,16 @@ i2c_dw_xfer_msg(struct dw_i2c_dev *dev)
>  
>  		/*
>  		 * Because we don't know the buffer length in the
> -		 * I2C_FUNC_SMBUS_BLOCK_DATA case, we can't stop
> -		 * the transaction here.
> +		 * 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 (buf_len > 0 || flags & I2C_M_RECV_LEN) {
> +		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;
> @@ -495,6 +501,13 @@ 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;
>  
> +	/*
> +	 * Received buffer length, re-enable TX_EMPTY interrupt
> +	 * to resume the SMBUS transaction.
> +	 */
> +	regmap_update_bits(dev->map, DW_IC_INTR_MASK, DW_IC_INTR_TX_EMPTY,
> +			   DW_IC_INTR_TX_EMPTY);
> +
>  	return len;
>  }
>  
> -- 
> 2.25.1
>