linux-kernel - Re: [PATCH v3 4/7] i2c: aspeed: Acknowledge Tx done w/wo ACK irq late

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Message-ID: <b082d8a8-cc96-7bc1-6ca4-589ab5ac677e@os.amperecomputing.com>
Date:   Thu, 20 May 2021 20:52:15 +0700
From:   Quan Nguyen <quan@...amperecomputing.com>
To:     Joel Stanley <joel@....id.au>, Guenter Roeck <linux@...ck-us.net>
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 4/7] i2c: aspeed: Acknowledge Tx done w/wo ACK irq late

On 20/05/2021 06:43, Joel Stanley wrote:
> On Wed, 19 May 2021 at 07:50, Quan Nguyen <quan@...amperecomputing.com> wrote:
>>
>> With Tx done w/wo ACK are ack'ed early at beginning of irq handler,
> 
> Is w/wo a typo? If not, please write the full words ("with and without")
> 
It is "with and without", will fix in next version

>> it is observed that, usually, the Tx done with Ack irq raises in the
>> READ REQUESTED state. This is unexpected and complaint as below appear:
>> "Unexpected Ack on read request"
>>
>> Assumed that Tx done should only be ack'ed once it was truly processed,
>> switch to late ack'ed this two irqs and seen this issue go away through
>> test with AST2500..
> 
> Please read Guneter's commit message
> 2be6b47211e17e6c90ead40d24d2a5cc815f2d5c to confirm that your changes
> do not invalidate the fix that they made.  Add them to CC for review.
> 
> Again, this is a fix that is independent of the ssif work. Please send
> it separately with a Fixes line.
> 
Will do and separate this patch into other series in next version.

>>
>> Signed-off-by: Quan Nguyen <quan@...amperecomputing.com>
>> ---
>> v3:
>>    + First introduce in v3 [Quan]
>>
>>   drivers/i2c/busses/i2c-aspeed.c | 26 ++++++++++++++++++--------
>>   1 file changed, 18 insertions(+), 8 deletions(-)
>>
>> diff --git a/drivers/i2c/busses/i2c-aspeed.c b/drivers/i2c/busses/i2c-aspeed.c
>> index 3fb37c3f23d4..b2e9c8f0ddf7 100644
>> --- a/drivers/i2c/busses/i2c-aspeed.c
>> +++ b/drivers/i2c/busses/i2c-aspeed.c
>> @@ -606,8 +606,12 @@ static irqreturn_t aspeed_i2c_bus_irq(int irq, void *dev_id)
>>
>>          spin_lock(&bus->lock);
>>          irq_received = readl(bus->base + ASPEED_I2C_INTR_STS_REG);
>> -       /* Ack all interrupts except for Rx done */
>> -       writel(irq_received & ~ASPEED_I2CD_INTR_RX_DONE,
>> +       /*
>> +        * Ack all interrupts except for Rx done and
>> +        * Tx done with/without ACK
> 
> Nit: this comment can be on one line.
> 
Thanks, will fix.
> 
>> +        */
>> +       writel(irq_received &
>> +              ~(ASPEED_I2CD_INTR_RX_DONE | ASPEED_I2CD_INTR_TX_ACK | ASPEED_I2CD_INTR_TX_NAK),
>>                 bus->base + ASPEED_I2C_INTR_STS_REG);
>>          readl(bus->base + ASPEED_I2C_INTR_STS_REG);
>>          irq_received &= ASPEED_I2CD_INTR_RECV_MASK;
>> @@ -652,12 +656,18 @@ static irqreturn_t aspeed_i2c_bus_irq(int irq, void *dev_id)
>>                          "irq handled != irq. expected 0x%08x, but was 0x%08x\n",
>>                          irq_received, irq_handled);
>>
>> -       /* Ack Rx done */
>> -       if (irq_received & ASPEED_I2CD_INTR_RX_DONE) {
>> -               writel(ASPEED_I2CD_INTR_RX_DONE,
>> -                      bus->base + ASPEED_I2C_INTR_STS_REG);
>> -               readl(bus->base + ASPEED_I2C_INTR_STS_REG);
>> -       }
>> +       /* Ack Rx done and Tx done with/without ACK */
>> +       /* Note: Re-use irq_handled variable */
> 
> I'm not sure what this note means.
> 
>> +       irq_handled = 0;
>> +       if (irq_received & ASPEED_I2CD_INTR_RX_DONE)
>> +               irq_handled |= ASPEED_I2CD_INTR_RX_DONE;
>> +       if (irq_received & ASPEED_I2CD_INTR_TX_ACK)
>> +               irq_handled |= ASPEED_I2CD_INTR_TX_ACK;
>> +       if (irq_received & ASPEED_I2CD_INTR_TX_NAK)
>> +               irq_handled |= ASPEED_I2CD_INTR_TX_NAK;
>> +       writel(irq_handled, bus->base + ASPEED_I2C_INTR_STS_REG);
> 
> Are you intentionally only acking the bits that are set when we read
> from STS_REG at the start of the handler? If not, we could write this
> instead:
> 
> writel(ASPEED_I2CD_INTR_RX_DONE | ASPEED_I2CD_INTR_TX_ACK |
> ASPEED_I2CD_INTR_TX_NAK,
>          bus->base + ASPEED_I2C_INTR_STS_REG);
> 
> If you only want to ack the bits that are set, then do this:
> 
>    writel(irq_received &
>              (ASPEED_I2CD_INTR_RX_DONE | ASPEED_I2CD_INTR_TX_ACK |
> ASPEED_I2CD_INTR_TX_NAK),
>           bus->base + ASPEED_I2C_INTR_STS_REG);
> 
> That way, you can avoid all of the tests.
> 
Thanks, will fix this in next version.

>> +       readl(bus->base + ASPEED_I2C_INTR_STS_REG);
> 
> When you move this, please add a comment that reminds us why we do a
> write-then-read (see commit c926c87b8e36dcc0ea5c2a0a0227ed4f32d0516a).
> 
Will fix in next version.
>> +
>>          spin_unlock(&bus->lock);
>>          return irq_remaining ? IRQ_NONE : IRQ_HANDLED;
>>   }
>> --
>> 2.28.0
>>