Re: [PATCH v2 RESEND 1/2] i2c: aspeed: Fix unhandled Tx done with NAK

[Quan Nguyen <quan@os.amperecomputing.com>]

On 30/11/2023 08:20, Andrew Jeffery wrote:
> On Wed, 2023-11-29 at 16:03 +0700, Quan Nguyen wrote:
>>
>> On 29/11/2023 07:19, Andrew Jeffery wrote:
>>> On Tue, 2023-11-28 at 14:52 +0700, Quan Nguyen wrote:
>>>> Under normal conditions, after the last byte is sent by the Slave, the
>>>> TX_NAK interrupt is raised.  However, it is also observed that
>>>> sometimes the Master issues the next transaction too quickly while the
>>>> Slave IRQ handler is not yet invoked and the TX_NAK interrupt for the
>>>> last byte of the previous READ_PROCESSED state has not been ack’ed.
>>>> This TX_NAK interrupt is then raised together with SLAVE_MATCH interrupt
>>>> and RX_DONE interrupt of the next coming transaction from Master. The
>>>> Slave IRQ handler currently handles the SLAVE_MATCH and RX_DONE, but
>>>> ignores the TX_NAK, causing complaints such as
>>>> "aspeed-i2c-bus 1e78a040.i2c-bus: irq handled != irq. Expected
>>>> 0x00000086, but was 0x00000084"
>>>>
>>>> This commit adds code to handle this case by emitting a SLAVE_STOP event
>>>> for the TX_NAK before processing the RX_DONE for the coming transaction
>>>> from the Master.
>>>>
>>>> Fixes: f9eb91350bb2 ("i2c: aspeed: added slave support for Aspeed I2C driver")
>>>> Signed-off-by: Quan Nguyen <quan@os.amperecomputing.com>
>>>> ---
>>>> v2:
>>>>     + Split to separate series [Joel]
>>>>     + Added the Fixes line [Joel]
>>>>     + Revised commit message [Quan]
>>>>
>>>> v1:
>>>>     + First introduced in
>>>> https://lore.kernel.org/all/20210519074934.20712-1-quan@os.amperecomputing.com/
>>>> ---
>>>>    drivers/i2c/busses/i2c-aspeed.c | 5 +++++
>>>>    1 file changed, 5 insertions(+)
>>>>
>>>> diff --git a/drivers/i2c/busses/i2c-aspeed.c b/drivers/i2c/busses/i2c-aspeed.c
>>>> index 28e2a5fc4528..79476b46285b 100644
>>>> --- a/drivers/i2c/busses/i2c-aspeed.c
>>>> +++ b/drivers/i2c/busses/i2c-aspeed.c
>>>> @@ -253,6 +253,11 @@ static u32 aspeed_i2c_slave_irq(struct aspeed_i2c_bus *bus, u32 irq_status)
>>>>    
>>>>    	/* Slave was requested, restart state machine. */
>>>>    	if (irq_status & ASPEED_I2CD_INTR_SLAVE_MATCH) {
>>>> +		if (irq_status & ASPEED_I2CD_INTR_TX_NAK &&
>>>> +		    bus->slave_state == ASPEED_I2C_SLAVE_READ_PROCESSED) {
>>>> +			irq_handled |= ASPEED_I2CD_INTR_TX_NAK;
>>>> +			i2c_slave_event(slave, I2C_SLAVE_STOP, &value);
>>>> +		}
>>>
>>> So we're already (partially) processing this a bit later on line 287:
>>>
>>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/i2c/busses/i2c-aspeed.c?h=v6.7-rc3#n287
>>>
>>
>> Thanks Andrew for the review.
>>
>> I think it's worth noting that the byte mode is used in this case.
>>
>> About the code you mentioned, it is for the general process of single
>> Slave transmission with NAK which should be interpret as I2C_SLAVE_STOP
>> event.
>>
>> In this case, there is a mix of Slave events:
>>
>>     + I2C_SLAVE_STOP (due to INTR_TX_NAK, BIT(1) of previous transaction)
>>     + Followed by I2C_SLAVE_[READ|WRITE]_REQUESTED (due to
>> INTR_SLAVE_MATCH and INTR_RX_DONE, BIT(7) and BIT(2), of next transaction)
>>
>> That is the reason we need to emit the I2C_SLAVE_STOP first for Slave
>> backend to process.
>>
>>>   From the description of the problem in the commit message it sounds
>>> like the ordering of the interrupt processing is incorrect.
>>
>> Yes, this is correct as per my explanation above.
>>
>> Prior to
>>> this patch we have the following abstract ordering of interrupt
>>> processing:
>>>
>>> 1. Process ASPEED_I2CD_INTR_SLAVE_MATCH
>>> 2. Process ASPEED_I2CD_INTR_TX_NAK when in ASPEED_I2C_SLAVE_READ_PROCESSED
>>>
>>
>>   From my test, the flow is as below:
>>
>>     1. Process ASPEED_I2CD_INTR_SLAVE_MATCH, slave_state is set to
>> ASPEED_I2C_SLAVE_START
>>     2. As there is INTR_RX_DONE and slave_state is
>> ASPEED_I2C_SLAVE_START, depends on the data received, the slave_state
>> moves to either ASPEED_I2C_SLAVE_[READ|WRITE]_REQUESTED.
>>     3. When reach to the if statement to process INTR_TX_NAK, slave_state
>> is already moves to either ASPEED_I2C_SLAVE_[READ|WRITE]_REQUESTED, not
>> in ASPEED_I2C_SLAVE_READ_PROCESSED anymore. This eventually evaluate as
>> false and the if statement is bypass. IOW, this INTR_TX_NAK is not process.
>>
>>> With this patch we have:
>>>
>>> 1. If ASPEED_I2CD_INTR_SLAVE_MATCH then process ASPEED_I2CD_INTR_TX_NAK when in ASPEED_I2C_SLAVE_READ_PROCESSED
>>> 2. Process ASPEED_I2CD_INTR_SLAVE_MATCH
>>> 3. Process ASPEED_I2CD_INTR_TX_NAK when in ASPEED_I2C_SLAVE_READ_PROCESSED
>>>
>>
>> With this patch:
>>
>>     0. The I2C_SLAVE_STOP is emitted to backend Slave driver first to
>> complete the previous transaction. And let the rest process as before
>> this patch.
>>
>>     1. Process ASPEED_I2CD_INTR_SLAVE_MATCH, slave_state is set to
>> ASPEED_I2C_SLAVE_START
>>     2. As there is INTR_RX_DONE and slave_state is
>> ASPEED_I2C_SLAVE_START, depends on the data received, the slave_state
>> moves to either ASPEED_I2C_SLAVE_[READ|WRITE]_REQUESTED.
>>     3. When reach to the if statement to process INTR_TX_NAK, slave_state
>> is already moves to either ASPEED_I2C_SLAVE_[READ|WRITE]_REQUESTED, not
>> in ASPEED_I2C_SLAVE_READ_PROCESSED anymore. This eventually evaluated as
>> false and the if statement is bypass. IOW, this INTR_TX_NAK is not process.
>>
>>> That feels a bit complex and redundant. What I think we can have is:
>>>
>>> 1. Process ASPEED_I2CD_INTR_TX_NAK when in ASPEED_I2C_SLAVE_READ_PROCESSED
>>> 1. Process ASPEED_I2CD_INTR_SLAVE_MATCH
>>>
>>> Moving back from the abstract to the concrete, implementing what I
>>> believe we need would look something like this patch:
>>>
>>> diff --git a/drivers/i2c/busses/i2c-aspeed.c b/drivers/i2c/busses/i2c-aspeed.c
>>> index 28e2a5fc4528..98dd0f35c9d3 100644
>>> --- a/drivers/i2c/busses/i2c-aspeed.c
>>> +++ b/drivers/i2c/busses/i2c-aspeed.c
>>> @@ -251,6 +251,14 @@ static u32 aspeed_i2c_slave_irq(struct aspeed_i2c_bus *bus, u32 irq_status)
>>>    
>>>           command = readl(bus->base + ASPEED_I2C_CMD_REG);
>>>    
>>> +       /* Complete any active read */
>>> +       if (irq_status & ASPEED_I2CD_INTR_TX_NAK &&
>>> +           bus->slave_state == ASPEED_I2C_SLAVE_READ_PROCESSED) {
>>> +               irq_handled |= ASPEED_I2CD_INTR_TX_NAK;
>>> +               i2c_slave_event(slave, I2C_SLAVE_STOP, &value);
>>> +               bus->slave_state = ASPEED_I2C_SLAVE_STOP;
>>> +       }
>>> +
>>
>> It is not confirmed through test yet but I'm afraid the switch case part
>> will emit another I2C_SLAVE_STOP event in case there is no mix of
>> interrupts.
> 
> Ah, good catch. I think we can rework things a bit to rationalise the
> logic at the expense a bigger diff. What do you think about this? I've
> boot tested it on an ast2600-evb and poked at some NVMe drives over
> MCTP to exercise the slave path.
> 
> diff --git a/drivers/i2c/busses/i2c-aspeed.c b/drivers/i2c/busses/i2c-aspeed.c
> index aec8966bceab..3c9333a12967 100644
> --- a/drivers/i2c/busses/i2c-aspeed.c
> +++ b/drivers/i2c/busses/i2c-aspeed.c
> @@ -249,18 +249,47 @@ static u32 aspeed_i2c_slave_irq(struct aspeed_i2c_bus *bus, u32 irq_status)
>   	if (!slave)
>   		return 0;
>   
> -	command = readl(bus->base + ASPEED_I2C_CMD_REG);
> +	/*
> +	 * Handle stop conditions early, prior to SLAVE_MATCH. Some masters may drive
> +	 * transfers with low enough latency between the nak/stop phase of the current
> +	 * command and the start/address phase of the following command that the
> +	 * interrupts are coalesced by the time we process them.
> +	 */
> +
> +	if (irq_status & ASPEED_I2CD_INTR_NORMAL_STOP) {
> +		irq_handled |= ASPEED_I2CD_INTR_NORMAL_STOP;
> +		bus->slave_state = ASPEED_I2C_SLAVE_STOP;
> +	}
> +
> +	if (irq_status & ASPEED_I2CD_INTR_TX_NAK &&
> +	    bus->slave_state == ASPEED_I2C_SLAVE_READ_PROCESSED) {
> +		irq_handled |= ASPEED_I2CD_INTR_TX_NAK;
> +		bus->slave_state = ASPEED_I2C_SLAVE_STOP;
> +	}
> +
> +	/* Propagate any stop conditions to the slave implementation */
> +	if (bus->slave_state == ASPEED_I2C_SLAVE_STOP) {
> +		i2c_slave_event(slave, I2C_SLAVE_STOP, &value);
> +		bus->slave_state = ASPEED_I2C_SLAVE_INACTIVE;
> +	}
>   
> -	/* Slave was requested, restart state machine. */
> +	/*
> +	 * Now that we've dealt with any potentially coalesced stop conditions,
> +	 * address any start conditions.
> +	 */
>   	if (irq_status & ASPEED_I2CD_INTR_SLAVE_MATCH) {
>   		irq_handled |= ASPEED_I2CD_INTR_SLAVE_MATCH;
>   		bus->slave_state = ASPEED_I2C_SLAVE_START;
>   	}
>   
> -	/* Slave is not currently active, irq was for someone else. */
> +	/*
> +	 * If the slave has been stopped and not started then slave interrupt handling
> +	 * is complete.
> +	 */
>   	if (bus->slave_state == ASPEED_I2C_SLAVE_INACTIVE)
>   		return irq_handled;
>   
> +	command = readl(bus->base + ASPEED_I2C_CMD_REG);
>   	dev_dbg(bus->dev, "slave irq status 0x%08x, cmd 0x%08x\n",
>   		irq_status, command);
>   
> @@ -279,17 +308,6 @@ static u32 aspeed_i2c_slave_irq(struct aspeed_i2c_bus *bus, u32 irq_status)
>   		irq_handled |= ASPEED_I2CD_INTR_RX_DONE;
>   	}
>   
> -	/* Slave was asked to stop. */
> -	if (irq_status & ASPEED_I2CD_INTR_NORMAL_STOP) {
> -		irq_handled |= ASPEED_I2CD_INTR_NORMAL_STOP;
> -		bus->slave_state = ASPEED_I2C_SLAVE_STOP;
> -	}
> -	if (irq_status & ASPEED_I2CD_INTR_TX_NAK &&
> -	    bus->slave_state == ASPEED_I2C_SLAVE_READ_PROCESSED) {
> -		irq_handled |= ASPEED_I2CD_INTR_TX_NAK;
> -		bus->slave_state = ASPEED_I2C_SLAVE_STOP;
> -	}
> -
>   	switch (bus->slave_state) {
>   	case ASPEED_I2C_SLAVE_READ_REQUESTED:
>   		if (unlikely(irq_status & ASPEED_I2CD_INTR_TX_ACK))
> @@ -324,8 +342,7 @@ static u32 aspeed_i2c_slave_irq(struct aspeed_i2c_bus *bus, u32 irq_status)
>   		i2c_slave_event(slave, I2C_SLAVE_WRITE_RECEIVED, &value);
>   		break;
>   	case ASPEED_I2C_SLAVE_STOP:
> -		i2c_slave_event(slave, I2C_SLAVE_STOP, &value);
> -		bus->slave_state = ASPEED_I2C_SLAVE_INACTIVE;
> +		/* Stop event handling is done early. Unreachable. */
>   		break;
>   	case ASPEED_I2C_SLAVE_START:
>   		/* Slave was just started. Waiting for the next event. */;

Yes, this looks much better. I'll confirm these changes through test and 
will post the next version ASAP.

Thanks a lot for the review,
- Quan