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

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Message-ID: <3f37c359-1c71-421f-b7d9-054696735adc@os.amperecomputing.com>
Date:   Wed, 29 Nov 2023 16:03:11 +0700
From:   Quan Nguyen <quan@...amperecomputing.com>
To:     Andi Shyti <andi.shyti@...nel.org>
Cc:     Brendan Higgins <brendan.higgins@...ux.dev>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Joel Stanley <joel@....id.au>,
        Andrew Jeffery <andrew@...econstruct.com.au>,
        Wolfram Sang <wsa@...nel.org>,
        Jae Hyun Yoo <jae.hyun.yoo@...ux.intel.com>,
        Guenter Roeck <linux@...ck-us.net>, linux-i2c@...r.kernel.org,
        openbmc@...ts.ozlabs.org, linux-arm-kernel@...ts.infradead.org,
        linux-aspeed@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        Cosmo Chou <chou.cosmo@...il.com>,
        Open Source Submission <patches@...erecomputing.com>,
        Phong Vo <phong@...amperecomputing.com>,
        "Thang Q . Nguyen" <thang@...amperecomputing.com>
Subject: Re: [PATCH v2 RESEND 1/2] i2c: aspeed: Fix unhandled Tx done with NAK



On 29/11/2023 07:35, Andi Shyti wrote:
> Hi Quan,
> 
> On Tue, Nov 28, 2023 at 02:52:35PM +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@...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);
>> +		}
> 
> this is a duplicate of a later "if (...)" satement. What is the
> need for having them both?
> 
Thanks Andi for the review.

I assumed the if statement you mentioned is here in [1]. If so, then 
that is not duplicate.

[1] 
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/i2c/busses/i2c-aspeed.c?h=v6.7-rc3#n287


The if statement is to process the case when Slave sending data to 
Master but being NAK, the I2C_SLAVE_STOP event will emit later in 
switch-case statement. But it is only for the case INTR_TX_NAK without 
INTR_SLAVE_MATCH.

The new code is for the case of INTR_TX_NAK with INTR_SLAVE_MATCH. What 
it does is to detect if there is a mix of INTR_TX_NAK of previous i2c 
transaction and the start of new i2c transaction, indicate by 
INTR_SLAVE_MATCH which is only raised when Slave found its address 
matched on the first byte it received. If so, the new code will try to 
emit the I2C_SLAVE_STOP first to complete the previous transaction and 
process the rest as a new request.

So if this was the case (with INTR_SLAVE_MATCH), the INTR_RX_DONE should 
always raise with INTR_SLAVE_MATCH because Slave did receive the data 
which matched with its Slave address. And this will be translated into 
either I2C_SLAVE_[READ|WRITE]_REQUESTED and that make the if statement 
you mentioned [1] evaluate to false and skip.

So, in short, the new code is trying to handle the case of INTR_TX_NAK 
with INTR_SLAVE_MATCH first before let the rest process as normal.

Thanks,
- Quan