Re: [PATCH v2 RESEND 2/2] i2c: aspeed: Acknowledge Tx done with and without ACK irq late

Andi Shyti
2023-11-29T00:45:48Z

Hi Quan,

On Tue, Nov 28, 2023 at 02:52:36PM +0700, Quan Nguyen wrote:
> Commit 2be6b47211e1 ("i2c: aspeed: Acknowledge most interrupts early in
> interrupt handler") acknowledges most interrupts early before the slave
> irq handler is executed, except for the "Receive Done Interrupt status"
> which is acknowledged late in the interrupt.
> However, it is observed that the early acknowledgment of "Transmit Done
> Interrupt Status" (with ACK or NACK) often causes the interrupt to be
> raised in READ REQUEST state, resulting in "Unexpected ACK on read
> request." complaint messages.
>
> Assuming that the "Transmit Done" interrupt should only be acknowledged
> once it is truly processed, this commit fixes this issue by acknowledging
> this interrupt for both ACK and NACK cases late in the interrupt handler
> also.
>
> Fixes: 2be6b47211e1 ("i2c: aspeed: Acknowledge most interrupts early in interrupt handler")
> Signed-off-by: Quan Nguyen <quan@os.amperecomputing.com>
> ---
> v2:
> + Split to separate series [Joel]
> + Added the Fixes line [Joel]
> + Fixed multiline comment [Joel]
> + Refactor irq clearing code [Joel, Guenter]
> + Revised commit message [Joel]
> + Revised commit message [Quan]
> + About a note to remind why the readl() should immediately follow the
> writel() to fix the race condition when clearing irq status from commit
> c926c87b8e36 ("i2c: aspeed: Avoid i2c interrupt status clear race
> condition"), I think it looks straight forward in this patch and decided
> not to add that note. [Joel]
>
> v1:
> + First introduced in
> https://lore.kernel.org/all/20210519074934.20712-1-quan@os.amperecomputing.com/
> ---
> drivers/i2c/busses/i2c-aspeed.c | 17 +++++++++--------
> 1 file changed, 9 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/i2c/busses/i2c-aspeed.c b/drivers/i2c/busses/i2c-aspeed.c
> index 79476b46285b..3231f430e335 100644
> --- a/drivers/i2c/busses/i2c-aspeed.c
> +++ b/drivers/i2c/busses/i2c-aspeed.c
> @@ -611,8 +611,9 @@ 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 */
> + 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;
> @@ -657,12 +658,12 @@ 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 */
> + 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);

So, you are acknowledging everything here. Why wasn’t it done
this way in the first place?

I would appreciate a comment here from Guenter, whose commit you
are fixing.

Thanks,
Andi

> spin_unlock(&bus->lock);
> return irq_remaining ? IRQ_NONE : IRQ_HANDLED;
> }
> --
> 2.35.1