linux-kernel - [PATCH v2 2/3] i3c: dw: Add sysfs support for Device NACK Retry count

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Message-ID: <12309bfeaa271d0b008989b323ddbd7587849066.1763703573.git.adrianhoyin.ng@altera.com>
Date: Fri, 21 Nov 2025 14:21:49 +0800
From: adrianhoyin.ng@...era.com
To: alexandre.belloni@...tlin.com,
	Frank.Li@....com,
	linux-i3c@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Cc: adrianhoyin.ng@...era.com
Subject: [PATCH v2 2/3] i3c: dw: Add sysfs support for Device NACK Retry count

From: Adrian Ng Ho Yin <adrianhoyin.ng@...era.com>

The DesignWare I3C controller supports automatically retrying transactions
when a device NACKs. This is useful for slave devices that may be
temporarily busy and not ready to respond immediately.

Adds a controller-wide sysfs attribute, dev_nack_retry_count, to read or
adjust the retry count at runtime. Writes are clamped to the hardware
maximum of 3, and the updated value is programmed into all active DAT
entries.

Signed-off-by: Adrian Ng Ho Yin <adrianhoyin.ng@...era.com>
---
 drivers/i3c/master/dw-i3c-master.c | 64 ++++++++++++++++++++++++++++++
 drivers/i3c/master/dw-i3c-master.h |  1 +
 2 files changed, 65 insertions(+)

diff --git a/drivers/i3c/master/dw-i3c-master.c b/drivers/i3c/master/dw-i3c-master.c
index 9ceedf09c3b6..c43eba615d8a 100644
--- a/drivers/i3c/master/dw-i3c-master.c
+++ b/drivers/i3c/master/dw-i3c-master.c
@@ -204,8 +204,10 @@
 #define EXTENDED_CAPABILITY		0xe8
 #define SLAVE_CONFIG			0xec
 
+#define DW_I3C_DEV_NACK_RETRY_CNT_MAX	0x3
 #define DEV_ADDR_TABLE_IBI_MDB		BIT(12)
 #define DEV_ADDR_TABLE_SIR_REJECT	BIT(13)
+#define DEV_ADDR_TABLE_DEV_NACK_RETRY_CNT(x)	(((x) << 29) & GENMASK(30, 29))
 #define DEV_ADDR_TABLE_LEGACY_I2C_DEV	BIT(31)
 #define DEV_ADDR_TABLE_DYNAMIC_ADDR(x)	(((x) << 16) & GENMASK(23, 16))
 #define DEV_ADDR_TABLE_STATIC_ADDR(x)	((x) & GENMASK(6, 0))
@@ -295,6 +297,58 @@ to_dw_i3c_master(struct i3c_master_controller *master)
 	return container_of(master, struct dw_i3c_master, base);
 }
 
+static ssize_t dev_nack_retry_count_show(struct device *dev,
+					 struct device_attribute *attr,
+					 char *buf)
+{
+	struct dw_i3c_master *master = dev_get_drvdata(dev);
+
+	return sysfs_emit(buf, "%u\n", master->dev_nack_retry_cnt);
+}
+
+static ssize_t dev_nack_retry_count_store(struct device *dev,
+					  struct device_attribute *attr,
+					  const char *buf, size_t count)
+{
+	struct dw_i3c_master *master = dev_get_drvdata(dev);
+	unsigned long val;
+	int ret, i;
+	u32 reg;
+
+	ret = kstrtoul(buf, 0, &val);
+	if (ret)
+		return ret;
+
+	if (val > DW_I3C_DEV_NACK_RETRY_CNT_MAX) {
+		dev_warn(dev, "Value %lu exceeds maximum %d, clamping to max\n",
+			 val, DW_I3C_DEV_NACK_RETRY_CNT_MAX);
+		val = DW_I3C_DEV_NACK_RETRY_CNT_MAX;
+	}
+
+	master->dev_nack_retry_cnt = val;
+
+	/*
+	 * Update DAT entries for all currently attached devices.
+	 * We directly iterate through the master's device array.
+	 */
+	for (i = 0; i < master->maxdevs; i++) {
+		/* Skip free/empty slots */
+		if (master->free_pos & BIT(i))
+			continue;
+
+		reg = readl(master->regs +
+				DEV_ADDR_TABLE_LOC(master->datstartaddr, i));
+		reg &= ~GENMASK(30, 29);
+		reg |= DEV_ADDR_TABLE_DEV_NACK_RETRY_CNT(val);
+		writel(reg, master->regs +
+			DEV_ADDR_TABLE_LOC(master->datstartaddr, i));
+	}
+
+	return count;
+}
+
+static DEVICE_ATTR_RW(dev_nack_retry_count);
+
 static void dw_i3c_master_disable(struct dw_i3c_master *master)
 {
 	writel(readl(master->regs + DEVICE_CTRL) & ~DEV_CTRL_ENABLE,
@@ -1032,6 +1086,7 @@ static int dw_i3c_master_attach_i3c_dev(struct i3c_dev_desc *dev)
 	data->index = pos;
 	master->devs[pos].addr = dev->info.dyn_addr ? : dev->info.static_addr;
 	master->free_pos &= ~BIT(pos);
+	master->dev_nack_retry_cnt = 0;
 	i3c_dev_set_master_data(dev, data);
 
 	writel(DEV_ADDR_TABLE_DYNAMIC_ADDR(master->devs[pos].addr),
@@ -1598,6 +1653,12 @@ int dw_i3c_common_probe(struct dw_i3c_master *master,
 	if (ret)
 		goto err_disable_pm;
 
+	dev_set_drvdata(&master->base.dev, master);
+	ret = device_create_file(&master->base.dev, &dev_attr_dev_nack_retry_count);
+	if (ret)
+		dev_warn(&master->base.dev,
+			 "Failed to create dev_nack_retry_count sysfs: %d\n", ret);
+
 	return 0;
 
 err_disable_pm:
@@ -1617,6 +1678,9 @@ void dw_i3c_common_remove(struct dw_i3c_master *master)
 	cancel_work_sync(&master->hj_work);
 	i3c_master_unregister(&master->base);
 
+	device_remove_file(&master->base.dev, &dev_attr_dev_nack_retry_count);
+	dev_set_drvdata(&master->base.dev, NULL);
+
 	pm_runtime_disable(master->dev);
 	pm_runtime_set_suspended(master->dev);
 	pm_runtime_dont_use_autosuspend(master->dev);
diff --git a/drivers/i3c/master/dw-i3c-master.h b/drivers/i3c/master/dw-i3c-master.h
index c5cb695c16ab..c87a0e87bfd9 100644
--- a/drivers/i3c/master/dw-i3c-master.h
+++ b/drivers/i3c/master/dw-i3c-master.h
@@ -51,6 +51,7 @@ struct dw_i3c_master {
 	u32 i2c_fm_timing;
 	u32 i2c_fmp_timing;
 	u32 quirks;
+	u32	dev_nack_retry_cnt;
 	/*
 	 * Per-device hardware data, used to manage the device address table
 	 * (DAT)
-- 
2.49.GIT