From mboxrd@z Thu Jan 1 00:00:00 1970 From: Quan Nguyen Date: Mon, 11 Dec 2023 11:06:27 +0700 Subject: [PATCH v3 2/2] i2c: aspeed: Acknowledge Tx done with and without ACK irq late In-Reply-To: <20231208033142.1673232-3-quan@os.amperecomputing.com> References: <20231208033142.1673232-1-quan@os.amperecomputing.com> <20231208033142.1673232-3-quan@os.amperecomputing.com> Message-ID: List-Id: To: linux-aspeed@lists.ozlabs.org MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit On 08/12/2023 10:31, 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 has been 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, that shows the > "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 that issue by acknowledging > interrupts for both ACK and NACK cases late in the interrupt handler. > > Fixes: 2be6b47211e1 ("i2c: aspeed: Acknowledge most interrupts early in interrupt handler") > Signed-off-by: Quan Nguyen > --- > v3: > + Fix the unconditinal write when ack the irqs [Andrew] > + Refactor the code to enhance code readability [Quan] > + Fix grammar in commit message [Quan] > > 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 at os.amperecomputing.com/ > --- > drivers/i2c/busses/i2c-aspeed.c | 21 +++++++++++++-------- > 1 file changed, 13 insertions(+), 8 deletions(-) > > diff --git a/drivers/i2c/busses/i2c-aspeed.c b/drivers/i2c/busses/i2c-aspeed.c > index 1c2a4f4c4e1b..967a26dd4ffa 100644 > --- a/drivers/i2c/busses/i2c-aspeed.c > +++ b/drivers/i2c/busses/i2c-aspeed.c > @@ -617,13 +617,19 @@ static u32 aspeed_i2c_master_irq(struct aspeed_i2c_bus *bus, u32 irq_status) > static irqreturn_t aspeed_i2c_bus_irq(int irq, void *dev_id) > { > struct aspeed_i2c_bus *bus = dev_id; > - u32 irq_received, irq_remaining, irq_handled; > + u32 irq_received, irq_remaining, irq_handled, irq_ack_last; > > 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, > - bus->base + ASPEED_I2C_INTR_STS_REG); > + > + /* > + * Early acking of INTR_RX_DONE and INTR_TX_[ACK|NAK] would indicate HW to > + * start receiving or sending new data, and this may cause a race condition > + * as the irq handler has not yet handled these irqs but is being acked. > + * Let's ack them late at the end of the irq handler when those are truly processed. > + */ > + irq_ack_last = ASPEED_I2CD_INTR_RX_DONE | ASPEED_I2CD_INTR_TX_ACK | ASPEED_I2CD_INTR_TX_NAK; > + writel(irq_received & ~irq_ack_last, bus->base + ASPEED_I2C_INTR_STS_REG); As there will be v4, I'd like to improve this line of code a bit. During debug, there are significant number of times when the irq_received has the value of 0x00000004 (INTR_RX_DONE) or 0x00000001 (INTR_TX_ACK). This makes the "irq_received & ~irq_ack_last" turn out to be 0. AFAIK, it does not make sense to keep repeatedly writing the 0 to the HW then try to re-read it with readl() every time. I'd like to change this HW access conditionally to avoid those unnecessary access. The change would looks like below: diff --git a/drivers/i2c/busses/i2c-aspeed.c b/drivers/i2c/busses/i2c-aspeed.c index 5511fd46a65e..0f67218cf04a 100644 --- a/drivers/i2c/busses/i2c-aspeed.c +++ b/drivers/i2c/busses/i2c-aspeed.c @@ -93,6 +93,10 @@ ASPEED_I2CD_INTR_RX_DONE | \ ASPEED_I2CD_INTR_TX_NAK | \ ASPEED_I2CD_INTR_TX_ACK) +#define ASPEED_I2CD_INTR_ACK_RX_TX \ + (ASPEED_I2CD_INTR_RX_DONE | \ + ASPEED_I2CD_INTR_TX_ACK | \ + ASPEED_I2CD_INTR_TX_NAK) /* 0x14 : I2CD Command/Status Register */ #define ASPEED_I2CD_SCL_LINE_STS BIT(18) @@ -622,10 +626,19 @@ 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, - bus->base + ASPEED_I2C_INTR_STS_REG); - readl(bus->base + ASPEED_I2C_INTR_STS_REG); + + /* + * Early acking of INTR_RX_DONE and INTR_TX_[ACK|NAK] would + ... + */ + if (irq_received & ~ASPEED_I2CD_INTR_ACK_RX_TX) { + writel(irq_received & ~ASPEED_I2CD_INTR_ACK_RX_TX, + bus->base + ASPEED_I2C_INTR_STS_REG); + readl(bus->base + ASPEED_I2C_INTR_STS_REG); + } + irq_received &= ASPEED_I2CD_INTR_RECV_MASK; irq_remaining = irq_received; Thanks, - Quan