linux-kernel - [PATCH v1 1/2] i3c: master: svc: Receive IBI requests in interrupt context

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Message-Id: <20250415051808.88091-2-yschu@nuvoton.com>
Date: Tue, 15 Apr 2025 13:18:07 +0800
From: Stanley Chu <stanley.chuys@...il.com>
To: frank.li@....com,
	miquel.raynal@...tlin.com,
	alexandre.belloni@...tlin.com,
	linux-i3c@...ts.infradead.org
Cc: linux-kernel@...r.kernel.org,
	tomer.maimon@...oton.com,
	kwliu@...oton.com,
	yschu@...oton.com
Subject: [PATCH v1 1/2] i3c: master: svc: Receive IBI requests in interrupt context

From: Stanley Chu <yschu@...oton.com>

Moving the job from workqueue to ISR for two reasons.

1. Improve bus utilization.
If the requests are postponed to be received in the workqueue thread,
the SDA line remains low for a long time while the system loading is
high. During this period, the bus is not available for other targets
to raise requests.

2. Ensure prompt response to requests.
For timing-critical requests, the target may encouter a failure or the
event is missed if the request is not received in time.

IBI request is short, ISR can receive the data quickly and then queue a
work to handle it in the bottom half.

Signed-off-by: Stanley Chu <yschu@...oton.com>
---
 drivers/i3c/master/svc-i3c-master.c | 25 ++++++++++---------------
 1 file changed, 10 insertions(+), 15 deletions(-)

diff --git a/drivers/i3c/master/svc-i3c-master.c b/drivers/i3c/master/svc-i3c-master.c
index 85e16de208d3..7ceaf3ec45bb 100644
--- a/drivers/i3c/master/svc-i3c-master.c
+++ b/drivers/i3c/master/svc-i3c-master.c
@@ -201,7 +201,6 @@ struct svc_i3c_drvdata {
  * @addrs: Array containing the dynamic addresses of each attached device
  * @descs: Array of descriptors, one per attached device
  * @hj_work: Hot-join work
- * @ibi_work: IBI work
  * @irq: Main interrupt
  * @pclk: System clock
  * @fclk: Fast clock (bus)
@@ -229,7 +228,6 @@ struct svc_i3c_master {
 	u8 addrs[SVC_I3C_MAX_DEVS];
 	struct i3c_dev_desc *descs[SVC_I3C_MAX_DEVS];
 	struct work_struct hj_work;
-	struct work_struct ibi_work;
 	int irq;
 	struct clk *pclk;
 	struct clk *fclk;
@@ -487,9 +485,8 @@ static int svc_i3c_master_handle_ibi_won(struct svc_i3c_master *master, u32 msta
 	return ret;
 }
 
-static void svc_i3c_master_ibi_work(struct work_struct *work)
+static void svc_i3c_master_ibi_isr(struct svc_i3c_master *master)
 {
-	struct svc_i3c_master *master = container_of(work, struct svc_i3c_master, ibi_work);
 	struct svc_i3c_i2c_dev_data *data;
 	unsigned int ibitype, ibiaddr;
 	struct i3c_dev_desc *dev;
@@ -504,7 +501,7 @@ static void svc_i3c_master_ibi_work(struct work_struct *work)
 	 * schedule during the whole I3C transaction, otherwise, the I3C bus timeout may happen if
 	 * any irq or schedule happen during transaction.
 	 */
-	guard(spinlock_irqsave)(&master->xferqueue.lock);
+	guard(spinlock)(&master->xferqueue.lock);
 
 	/*
 	 * IBIWON may be set before SVC_I3C_MCTRL_REQUEST_AUTO_IBI, causing
@@ -530,7 +527,7 @@ static void svc_i3c_master_ibi_work(struct work_struct *work)
 	if (ret) {
 		dev_err(master->dev, "Timeout when polling for IBIWON\n");
 		svc_i3c_master_emit_stop(master);
-		goto reenable_ibis;
+		return;
 	}
 
 	status = readl(master->regs + SVC_I3C_MSTATUS);
@@ -574,7 +571,7 @@ static void svc_i3c_master_ibi_work(struct work_struct *work)
 
 		svc_i3c_master_emit_stop(master);
 
-		goto reenable_ibis;
+		return;
 	}
 
 	/* Handle the non critical tasks */
@@ -597,9 +594,6 @@ static void svc_i3c_master_ibi_work(struct work_struct *work)
 	default:
 		break;
 	}
-
-reenable_ibis:
-	svc_i3c_master_enable_interrupts(master, SVC_I3C_MINT_SLVSTART);
 }
 
 static irqreturn_t svc_i3c_master_irq_handler(int irq, void *dev_id)
@@ -618,10 +612,12 @@ static irqreturn_t svc_i3c_master_irq_handler(int irq, void *dev_id)
 	    !SVC_I3C_MSTATUS_STATE_SLVREQ(active))
 		return IRQ_HANDLED;
 
-	svc_i3c_master_disable_interrupts(master);
-
-	/* Handle the interrupt in a non atomic context */
-	queue_work(master->base.wq, &master->ibi_work);
+	/*
+	 * The SDA line remains low until the request is processed.
+	 * Receive the request in the interrupt context to respond promptly
+	 * and restore the bus to idle state.
+	 */
+	svc_i3c_master_ibi_isr(master);
 
 	return IRQ_HANDLED;
 }
@@ -1947,7 +1943,6 @@ static int svc_i3c_master_probe(struct platform_device *pdev)
 		return ret;
 
 	INIT_WORK(&master->hj_work, svc_i3c_master_hj_work);
-	INIT_WORK(&master->ibi_work, svc_i3c_master_ibi_work);
 	mutex_init(&master->lock);
 
 	ret = devm_request_irq(dev, master->irq, svc_i3c_master_irq_handler,
-- 
2.34.1