linux-kernel - Re: [PATCH v1] i2c: designware: fix idx_write

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Message-ID: <ZG3uF1WOv1MhTV3f@smile.fi.intel.com>
Date:   Wed, 24 May 2023 13:59:35 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     David Zheng <david.zheng@...el.com>
Cc:     linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org,
        jarkko.nikula@...ux.intel.com, mika.westerberg@...ux.intel.com,
        jsd@...ihalf.com
Subject: Re: [PATCH v1] i2c: designware: fix idx_write_cnt in read loop

On Tue, May 23, 2023 at 09:46:21AM -0700, David Zheng wrote:
> With IC_INTR_RX_FULL slave interrupt handler reads data in a loop until
> RX FIFO is empty. When testing with the slave-eeprom, each transaction
> has 2 bytes for address/index and 1 byte for value, the address byte
> can be written as data byte due to dropping STOP condition.
> 
> In the test below, the master continuously writes to the slave, first 2
> bytes are index, 3rd byte is value and follow by a STOP condition.
> 
>  i2c_write: i2c-3 #0 a=04b f=0000 l=3 [00-D1-D1]
>  i2c_write: i2c-3 #0 a=04b f=0000 l=3 [00-D2-D2]
>  i2c_write: i2c-3 #0 a=04b f=0000 l=3 [00-D3-D3]
> 
> Upon receiving STOP condition slave eeprom would reset `idx_write_cnt` so
> next 2 bytes can be treated as buffer index for upcoming transaction.
> Supposedly the slave eeprom buffer would be written as
> 
>  EEPROM[0x00D1] = 0xD1
>  EEPROM[0x00D2] = 0xD2
>  EEPROM[0x00D3] = 0xD3
> 
> When CPU load is high the slave irq handler may not read fast enough,
> the interrupt status can be seen as 0x204 with both DW_IC_INTR_STOP_DET
> (0x200) and DW_IC_INTR_RX_FULL (0x4) bits. The slave device may see
> the transactions below.
> 
>  0x1 STATUS SLAVE_ACTIVITY=0x1 : RAW_INTR_STAT=0x1594 : INTR_STAT=0x4
>  0x1 STATUS SLAVE_ACTIVITY=0x1 : RAW_INTR_STAT=0x1594 : INTR_STAT=0x4
>  0x1 STATUS SLAVE_ACTIVITY=0x1 : RAW_INTR_STAT=0x1594 : INTR_STAT=0x4
>  0x1 STATUS SLAVE_ACTIVITY=0x1 : RAW_INTR_STAT=0x1794 : INTR_STAT=0x204
>  0x1 STATUS SLAVE_ACTIVITY=0x0 : RAW_INTR_STAT=0x1790 : INTR_STAT=0x200
>  0x1 STATUS SLAVE_ACTIVITY=0x1 : RAW_INTR_STAT=0x1594 : INTR_STAT=0x4
>  0x1 STATUS SLAVE_ACTIVITY=0x1 : RAW_INTR_STAT=0x1594 : INTR_STAT=0x4
>  0x1 STATUS SLAVE_ACTIVITY=0x1 : RAW_INTR_STAT=0x1594 : INTR_STAT=0x4
> 
> After `D1` is received, read loop continues to read `00` which is the
> first bype of next index. Since STOP condition is ignored by the loop,
> eeprom buffer index increased to `D2` and `00` is written as value.
> 
> So the slave eeprom buffer becomes
> 
>  EEPROM[0x00D1] = 0xD1
>  EEPROM[0x00D2] = 0x00
>  EEPROM[0x00D3] = 0xD3
> 
> The fix is to use `FIRST_DATA_BYTE` (bit 11) in `IC_DATA_CMD` to split
> the transactions. The first index byte in this case would have bit 11
> set. Check this indication to inject I2C_SLAVE_WRITE_REQUESTED event
> which will reset `idx_write_cnt` in slave eeprom.
> 
> Signed-off-by: David Zheng <david.zheng@...el.com>
> ---

Is it still v1? Otherwise you have wrong Subject (missing version) and missing
changelog here.

-- 
With Best Regards,
Andy Shevchenko