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Message-ID: <63e740bf-cd0c-4671-9254-6846048b0366@molgen.mpg.de>
Date: Thu, 19 Jun 2025 01:18:33 +0200
From: Paul Menzel <pmenzel@...gen.mpg.de>
To: Jian Zhang <zhangjian.3032@...edance.com>
Cc: Ryan Chen <ryan_chen@...eedtech.com>,
Benjamin Herrenschmidt <benh@...nel.crashing.org>,
Joel Stanley <joel@....id.au>, Andi Shyti <andi.shyti@...nel.org>,
Andrew Jeffery <andrew@...econstruct.com.au>, 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
Subject: Re: [PATCH] i2c: aspeed: change debug level in irq handler
Dear Jian,
Thank you for the patch.
Am 18.06.25 um 12:21 schrieb Jian Zhang:
> In interrupt context, using dev_err() can potentially cause latency
> or affect system responsiveness due to printing to console.
>
> In our scenario, under certain conditions, i2c1 repeatedly printed
> "irq handled != irq. expected ..." around 20 times within 1 second.
Any idea, why you hit this error at all?
> Each dev_err() log introduced approximately 10ms of blocking time,
> which delayed the handling of other interrupts — for example, i2c2.
>
> At the time, i2c2 was performing a PMBus firmware upgrade. The
> target device on i2c2 was time-sensitive, and the upgrade protocol
> was non-retryable. As a result, the delay caused by frequent error
> logging led to a timeout and ultimately a failed firmware upgrade.
>
> Frequent error printing in interrupt context can be dangerous,
> as it introduces latency and interferes with time-critical tasks.
> This patch changes the log level from dev_err() to dev_dbg() to
> reduce potential impact.
Thank you for the patch and the problem description. Hiding an error
condition behind debug level is also not good, as administrators might
miss hardware issues. I do not have a solution. Is there something
similar to WARN_ONCE? Maybe the level should be a warning instead of
error, because the system is often able to cope with this?
The code is from 2017, so should be well tested actually, shouldn’t it?
> Signed-off-by: Jian Zhang <zhangjian.3032@...edance.com>
> ---
> drivers/i2c/busses/i2c-aspeed.c | 18 +++++++++---------
> 1 file changed, 9 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/i2c/busses/i2c-aspeed.c b/drivers/i2c/busses/i2c-aspeed.c
> index 1550d3d552ae..38e23c826f39 100644
> --- a/drivers/i2c/busses/i2c-aspeed.c
> +++ b/drivers/i2c/busses/i2c-aspeed.c
> @@ -317,7 +317,7 @@ static u32 aspeed_i2c_slave_irq(struct aspeed_i2c_bus *bus, u32 irq_status)
> switch (bus->slave_state) {
> case ASPEED_I2C_SLAVE_READ_REQUESTED:
> if (unlikely(irq_status & ASPEED_I2CD_INTR_TX_ACK))
> - dev_err(bus->dev, "Unexpected ACK on read request.\n");
> + dev_dbg(bus->dev, "Unexpected ACK on read request.\n");
> bus->slave_state = ASPEED_I2C_SLAVE_READ_PROCESSED;
> i2c_slave_event(slave, I2C_SLAVE_READ_REQUESTED, &value);
> writel(value, bus->base + ASPEED_I2C_BYTE_BUF_REG);
> @@ -325,7 +325,7 @@ static u32 aspeed_i2c_slave_irq(struct aspeed_i2c_bus *bus, u32 irq_status)
> break;
> case ASPEED_I2C_SLAVE_READ_PROCESSED:
> if (unlikely(!(irq_status & ASPEED_I2CD_INTR_TX_ACK))) {
> - dev_err(bus->dev,
> + dev_dbg(bus->dev,
> "Expected ACK after processed read.\n");
> break;
> }
> @@ -354,7 +354,7 @@ static u32 aspeed_i2c_slave_irq(struct aspeed_i2c_bus *bus, u32 irq_status)
> /* Slave was just started. Waiting for the next event. */;
> break;
> default:
> - dev_err(bus->dev, "unknown slave_state: %d\n",
> + dev_dbg(bus->dev, "unknown slave_state: %d\n",
> bus->slave_state);
> bus->slave_state = ASPEED_I2C_SLAVE_INACTIVE;
> break;
> @@ -459,7 +459,7 @@ static u32 aspeed_i2c_master_irq(struct aspeed_i2c_bus *bus, u32 irq_status)
>
> /* We are in an invalid state; reset bus to a known state. */
> if (!bus->msgs) {
> - dev_err(bus->dev, "bus in unknown state. irq_status: 0x%x\n",
> + dev_dbg(bus->dev, "bus in unknown state. irq_status: 0x%x\n",
> irq_status);
> bus->cmd_err = -EIO;
> if (bus->master_state != ASPEED_I2C_MASTER_STOP &&
> @@ -523,7 +523,7 @@ static u32 aspeed_i2c_master_irq(struct aspeed_i2c_bus *bus, u32 irq_status)
> irq_handled |= ASPEED_I2CD_INTR_TX_NAK;
> goto error_and_stop;
> } else if (unlikely(!(irq_status & ASPEED_I2CD_INTR_TX_ACK))) {
> - dev_err(bus->dev, "slave failed to ACK TX\n");
> + dev_dbg(bus->dev, "slave failed to ACK TX\n");
> goto error_and_stop;
> }
> irq_handled |= ASPEED_I2CD_INTR_TX_ACK;
> @@ -546,7 +546,7 @@ static u32 aspeed_i2c_master_irq(struct aspeed_i2c_bus *bus, u32 irq_status)
> fallthrough;
> case ASPEED_I2C_MASTER_RX:
> if (unlikely(!(irq_status & ASPEED_I2CD_INTR_RX_DONE))) {
> - dev_err(bus->dev, "master failed to RX\n");
> + dev_dbg(bus->dev, "master failed to RX\n");
> goto error_and_stop;
> }
> irq_handled |= ASPEED_I2CD_INTR_RX_DONE;
> @@ -577,7 +577,7 @@ static u32 aspeed_i2c_master_irq(struct aspeed_i2c_bus *bus, u32 irq_status)
> goto out_no_complete;
> case ASPEED_I2C_MASTER_STOP:
> if (unlikely(!(irq_status & ASPEED_I2CD_INTR_NORMAL_STOP))) {
> - dev_err(bus->dev,
> + dev_dbg(bus->dev,
> "master failed to STOP. irq_status:0x%x\n",
> irq_status);
> bus->cmd_err = -EIO;
> @@ -589,7 +589,7 @@ static u32 aspeed_i2c_master_irq(struct aspeed_i2c_bus *bus, u32 irq_status)
> bus->master_state = ASPEED_I2C_MASTER_INACTIVE;
> goto out_complete;
> case ASPEED_I2C_MASTER_INACTIVE:
> - dev_err(bus->dev,
> + dev_dbg(bus->dev,
> "master received interrupt 0x%08x, but is inactive\n",
> irq_status);
> bus->cmd_err = -EIO;
> @@ -665,7 +665,7 @@ static irqreturn_t aspeed_i2c_bus_irq(int irq, void *dev_id)
>
> irq_remaining &= ~irq_handled;
> if (irq_remaining)
> - dev_err(bus->dev,
> + dev_dbg(bus->dev,
> "irq handled != irq. expected 0x%08x, but was 0x%08x\n",
> irq_received, irq_handled);
>
Kind regards,
Paul
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