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

[Andrew Jeffery <andrew@codeconstruct.com.au>]

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. */;

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