linux-kernel - Re: [PATCH v3 3/7] i2c: aspeed: Fix unhandled Tx done with NAK

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Message-ID: <d801bdc4-449b-fdbe-4784-acd13df1c063@os.amperecomputing.com>
Date:   Thu, 20 May 2021 21:15:20 +0700
From:   Quan Nguyen <quan@...amperecomputing.com>
To:     Ryan Chen <ryan_chen@...eedtech.com>, Joel Stanley <joel@....id.au>
Cc:     Corey Minyard <minyard@....org>, Rob Herring <robh+dt@...nel.org>,
        Andrew Jeffery <andrew@...id.au>,
        Brendan Higgins <brendanhiggins@...gle.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Wolfram Sang <wsa@...nel.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        "openipmi-developer@...ts.sourceforge.net" 
        <openipmi-developer@...ts.sourceforge.net>,
        devicetree <devicetree@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-aspeed <linux-aspeed@...ts.ozlabs.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
        Open Source Submission <patches@...erecomputing.com>,
        Phong Vo <phong@...amperecomputing.com>,
        "Thang Q . Nguyen" <thang@...amperecomputing.com>,
        OpenBMC Maillist <openbmc@...ts.ozlabs.org>
Subject: Re: [PATCH v3 3/7] i2c: aspeed: Fix unhandled Tx done with NAK

On 20/05/2021 18:28, Ryan Chen wrote:
>> -----Original Message-----
>> From: Joel Stanley <joel@....id.au>
>> Sent: Thursday, May 20, 2021 7:29 AM
>> To: Quan Nguyen <quan@...amperecomputing.com>; Ryan Chen
>> <ryan_chen@...eedtech.com>
>> Cc: Corey Minyard <minyard@....org>; Rob Herring <robh+dt@...nel.org>;
>> Andrew Jeffery <andrew@...id.au>; Brendan Higgins
>> <brendanhiggins@...gle.com>; Benjamin Herrenschmidt
>> <benh@...nel.crashing.org>; Wolfram Sang <wsa@...nel.org>; Philipp Zabel
>> <p.zabel@...gutronix.de>; openipmi-developer@...ts.sourceforge.net;
>> devicetree <devicetree@...r.kernel.org>; Linux ARM
>> <linux-arm-kernel@...ts.infradead.org>; linux-aspeed
>> <linux-aspeed@...ts.ozlabs.org>; Linux Kernel Mailing List
>> <linux-kernel@...r.kernel.org>; linux-i2c@...r.kernel.org; Open Source
>> Submission <patches@...erecomputing.com>; Phong Vo
>> <phong@...amperecomputing.com>; Thang Q . Nguyen
>> <thang@...amperecomputing.com>; OpenBMC Maillist
>> <openbmc@...ts.ozlabs.org>
>> Subject: Re: [PATCH v3 3/7] i2c: aspeed: Fix unhandled Tx done with NAK
>>
>> Ryan, can you please review this change?
>>
>> On Wed, 19 May 2021 at 07:50, Quan Nguyen
>> <quan@...amperecomputing.com> wrote:
>>>
>>> It is observed that in normal condition, when the last byte sent by
>>> slave, the Tx Done with NAK irq will raise.
>>> But it is also observed that sometimes master issues next transaction
>>> too quick while the slave irq handler is not yet invoked and Tx Done
>>> with NAK irq of last byte of previous READ PROCESSED was not ack'ed.
>>> This Tx Done with NAK irq is raised together with the Slave Match and
>>> Rx Done irq of the next coming transaction from master.
>>> Unfortunately, the current slave irq handler handles the Slave Match
>>> and Rx Done only in higher priority and ignore the Tx Done with NAK,
>>> causing the complain as below:
>>> "aspeed-i2c-bus 1e78a040.i2c-bus: irq handled != irq. expected
>>> 0x00000086, but was 0x00000084"
>>>
>>> This commit handles this case by emitting a Slave Stop event for the
>>> Tx Done with NAK before processing Slave Match and Rx Done for the
>>> coming transaction from master.
>>
>> It sounds like this patch is independent of the rest of the series, and can go in
>> on it's own. Please send it separately to the i2c maintainers and add a suitable
>> Fixes line, such as:
>>
>>    Fixes: f9eb91350bb2 ("i2c: aspeed: added slave support for Aspeed I2C
>> driver")
>>
>>>
>>> Signed-off-by: Quan Nguyen <quan@...amperecomputing.com>
>>> ---
>>> v3:
>>>    + First introduce in v3 [Quan]
>>>
>>>   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 724bf30600d6..3fb37c3f23d4
>>> 100644
>>> --- a/drivers/i2c/busses/i2c-aspeed.c
>>> +++ b/drivers/i2c/busses/i2c-aspeed.c
>>> @@ -254,6 +254,11 @@ 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) {
>>
>> Can you explain why you need to do this handing inside the SLAVE_MATCH
>> case?
>>
>> Could you instead move the TX_NAK handling to be above the SLAVE_MATCH
>> case?
>>
>>> +               if (irq_status & ASPEED_I2CD_INTR_TX_NAK &&
>>> +                   bus->slave_state ==
>>> + ASPEED_I2C_SLAVE_READ_PROCESSED) {
>>
>> Either way, this needs a comment to explain what we're working around.
>>
>>> +                       irq_handled |= ASPEED_I2CD_INTR_TX_NAK;
>>> +                       i2c_slave_event(slave, I2C_SLAVE_STOP,
>> &value);
> 
> According the patch assume slave receive TX_NAK will be go to SLAVE_STOP state?
> 
Hi Ryan,

As per my explain in other email, we need to emit one SLAVE_STOP event 
to complete the previous transaction before start processing for the 
next transaction.

- Quan

>>> +               }
>>>                  irq_handled |= ASPEED_I2CD_INTR_SLAVE_MATCH;
>>>                  bus->slave_state = ASPEED_I2C_SLAVE_START;
>>>          }
>>> --
>>> 2.28.0
>>>