linux-kernel - Re: [PATCH] i2c: designware: call i2c_dw_read_clear_intrbits

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Date:   Wed, 21 Oct 2020 15:22:13 +0300
From:   Jarkko Nikula <jarkko.nikula@...ux.intel.com>
To:     Michael Wu <michael.wu@...ics.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     Morgan Chang <morgan.chang@...ics.com>
Subject: Re: [PATCH] i2c: designware: call i2c_dw_read_clear_intrbits_slave()
 once

Hi

On 10/20/20 11:33 AM, Michael Wu wrote:
> i2c_dw_read_clear_intrbits_slave() was called per each interrupt handle.
> It caused some interrupt bits which haven't been handled yet were cleared,
> the corresponding handlers would do nothing due to interrupt bits been
> discarded. For example,
> 
> $ i2cset -f -y 2 0x42 0x00 0x41; dmesg -c
> [0][clear_intrbits]0x1 STATUS SLAVE_ACTIVITY=0x1 : RAW_INTR_STAT=0x514 : INTR_STAT=0x4
> [1][irq_handler   ]0x1 STATUS SLAVE_ACTIVITY=0x1 : RAW_INTR_STAT=0x514 : INTR_STAT=0x4
> WRITE_RECEIVED
> [0][clear_intrbits]0x1 STATUS SLAVE_ACTIVITY=0x0 : RAW_INTR_STAT=0x714 : INTR_STAT=0x204
> [1][irq_handler   ]0x1 STATUS SLAVE_ACTIVITY=0x0 : RAW_INTR_STAT=0x514 : INTR_STAT=0x4
> WRITE_RECEIVED
> 
>    t1: ISR with the 1st IC_INTR_RX_FULL.
>    t2: Clear listed IC_INTR bits by i2c_dw_read_clear_intrbits_slave().
>    t3: Enter i2c_dw_irq_handler_slave() and then do
>        i2c_slave_event(WRITE_RECEIVED) because
>        if (stat & DW_IC_INTR_RX_FULL).
>    t4: ISR with both IC_INTR_STOP_DET and the 2nd IC_INTR_RX_FULL.
>    t5: Clear listed IC_INTR bits by i2c_dw_read_clear_intrbits_slave(). The
>        current IC_INTR_STOP_DET is cleared by this
>        i2c_dw_read_clear_intrbits_slave().
>    t6: Enter i2c_dw_irq_handler_slave() and then do
>        i2c_slave_event(WRITE_RECEIVED) because
>        if (stat & DW_IC_INTR_RX_FULL).
>    t7: i2c_slave_event(STOP) never be done because IC_INTR_STOP_DET was
>        cleared in t5.
> 
> The root cause is that i2c_dw_read_clear_intrbits_slave() was called many
> times. Calling i2c_dw_read_clear_intrbits_slave() once in one ISR and take
> the returned stat for later handling is the solution.
> 
> Signed-off-by: Michael Wu <michael.wu@...ics.com>
> ---
>   drivers/i2c/busses/i2c-designware-slave.c | 16 +++++-----------
>   1 file changed, 5 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-designware-slave.c b/drivers/i2c/busses/i2c-designware-slave.c
> index 44974b53a626..02e7c5171827 100644
> --- a/drivers/i2c/busses/i2c-designware-slave.c
> +++ b/drivers/i2c/busses/i2c-designware-slave.c
> @@ -159,7 +159,6 @@ static int i2c_dw_irq_handler_slave(struct dw_i2c_dev *dev)
>   	u32 raw_stat, stat, enabled, tmp;
>   	u8 val = 0, slave_activity;
>   
> -	regmap_read(dev->map, DW_IC_INTR_STAT, &stat);
>   	regmap_read(dev->map, DW_IC_ENABLE, &enabled);
>   	regmap_read(dev->map, DW_IC_RAW_INTR_STAT, &raw_stat);
>   	regmap_read(dev->map, DW_IC_STATUS, &tmp);
> @@ -168,13 +167,11 @@ static int i2c_dw_irq_handler_slave(struct dw_i2c_dev *dev)
>   	if (!enabled || !(raw_stat & ~DW_IC_INTR_ACTIVITY) || !dev->slave)
>   		return 0;
>   
> +	stat = i2c_dw_read_clear_intrbits_slave(dev);
>   	dev_dbg(dev->dev,
>   		"%#x STATUS SLAVE_ACTIVITY=%#x : RAW_INTR_STAT=%#x : INTR_STAT=%#x\n",
>   		enabled, slave_activity, raw_stat, stat);
>   
> -	if ((stat & DW_IC_INTR_RX_FULL) && (stat & DW_IC_INTR_STOP_DET))
> -		i2c_slave_event(dev->slave, I2C_SLAVE_WRITE_REQUESTED, &val);
> -

...

> +
> +	if ((stat & DW_IC_INTR_RX_FULL) && (stat & DW_IC_INTR_STOP_DET))
> +		i2c_slave_event(dev->slave, I2C_SLAVE_WRITE_REQUESTED, &val);

Was this move a leftover that got committed by accident? I think it's 
better to have this logic change in another patch. Or was it even 
questionable to move the I2C_SLAVE_WRITE_REQUESTED reporting after all 
other?

Jarkko