i3c: mipi-i3c-hci-pci: Add LTR support for Intel controllers

Add support for Latency Tolerance Reporting (LTR) for Intel controllers.

Implement PM ->set_latency_tolerance() callback to set LTR register values.
Also expose LTR register values via debugfs.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Link: https://patch.msgid.link/20251128064038.55158-12-adrian.hunter@intel.com
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

Author: ahunter6

drivers/i3c/master/mipi-i3c-hci/mipi-i3c-hci-pci.c

@@ -7,17 +7,21 @@
  * Author: Jarkko Nikula <jarkko.nikula@linux.intel.com>
  */
 #include <linux/acpi.h>
+#include <linux/bitfield.h>
+#include <linux/debugfs.h>
 #include <linux/idr.h>
 #include <linux/iopoll.h>
 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/pci.h>
 #include <linux/platform_device.h>
+#include <linux/pm_qos.h>
 
 struct mipi_i3c_hci_pci {
 	struct pci_dev *pci;
 	struct platform_device *pdev;
 	const struct mipi_i3c_hci_pci_info *info;
+	void *private;
 };
 
 struct mipi_i3c_hci_pci_info {
@@ -34,6 +38,99 @@ static DEFINE_IDA(mipi_i3c_hci_pci_ida);
 #define INTEL_RESETS_RESET_DONE		BIT(1)
 #define INTEL_RESETS_TIMEOUT_US		(10 * USEC_PER_MSEC)
 
+#define INTEL_ACTIVELTR			0x0c
+#define INTEL_IDLELTR			0x10
+
+#define INTEL_LTR_REQ			BIT(15)
+#define INTEL_LTR_SCALE_MASK		GENMASK(11, 10)
+#define INTEL_LTR_SCALE_1US		FIELD_PREP(INTEL_LTR_SCALE_MASK, 2)
+#define INTEL_LTR_SCALE_32US		FIELD_PREP(INTEL_LTR_SCALE_MASK, 3)
+#define INTEL_LTR_VALUE_MASK		GENMASK(9, 0)
+
+struct intel_host {
+	void __iomem	*priv;
+	u32		active_ltr;
+	u32		idle_ltr;
+	struct dentry	*debugfs_root;
+};
+
+static void intel_cache_ltr(struct intel_host *host)
+{
+	host->active_ltr = readl(host->priv + INTEL_ACTIVELTR);
+	host->idle_ltr = readl(host->priv + INTEL_IDLELTR);
+}
+
+static void intel_ltr_set(struct device *dev, s32 val)
+{
+	struct mipi_i3c_hci_pci *hci = dev_get_drvdata(dev);
+	struct intel_host *host = hci->private;
+	u32 ltr;
+
+	/*
+	 * Program latency tolerance (LTR) accordingly what has been asked
+	 * by the PM QoS layer or disable it in case we were passed
+	 * negative value or PM_QOS_LATENCY_ANY.
+	 */
+	ltr = readl(host->priv + INTEL_ACTIVELTR);
+
+	if (val == PM_QOS_LATENCY_ANY || val < 0) {
+		ltr &= ~INTEL_LTR_REQ;
+	} else {
+		ltr |= INTEL_LTR_REQ;
+		ltr &= ~INTEL_LTR_SCALE_MASK;
+		ltr &= ~INTEL_LTR_VALUE_MASK;
+
+		if (val > INTEL_LTR_VALUE_MASK) {
+			val >>= 5;
+			if (val > INTEL_LTR_VALUE_MASK)
+				val = INTEL_LTR_VALUE_MASK;
+			ltr |= INTEL_LTR_SCALE_32US | val;
+		} else {
+			ltr |= INTEL_LTR_SCALE_1US | val;
+		}
+	}
+
+	if (ltr == host->active_ltr)
+		return;
+
+	writel(ltr, host->priv + INTEL_ACTIVELTR);
+	writel(ltr, host->priv + INTEL_IDLELTR);
+
+	/* Cache the values into intel_host structure */
+	intel_cache_ltr(host);
+}
+
+static void intel_ltr_expose(struct device *dev)
+{
+	dev->power.set_latency_tolerance = intel_ltr_set;
+	dev_pm_qos_expose_latency_tolerance(dev);
+}
+
+static void intel_ltr_hide(struct device *dev)
+{
+	dev_pm_qos_hide_latency_tolerance(dev);
+	dev->power.set_latency_tolerance = NULL;
+}
+
+static void intel_add_debugfs(struct mipi_i3c_hci_pci *hci)
+{
+	struct dentry *dir = debugfs_create_dir(dev_name(&hci->pci->dev), NULL);
+	struct intel_host *host = hci->private;
+
+	intel_cache_ltr(host);
+
+	host->debugfs_root = dir;
+	debugfs_create_x32("active_ltr", 0444, dir, &host->active_ltr);
+	debugfs_create_x32("idle_ltr", 0444, dir, &host->idle_ltr);
+}
+
+static void intel_remove_debugfs(struct mipi_i3c_hci_pci *hci)
+{
+	struct intel_host *host = hci->private;
+
+	debugfs_remove_recursive(host->debugfs_root);
+}
+
 static void intel_reset(void __iomem *priv)
 {
 	u32 reg;
@@ -55,20 +152,34 @@ static void __iomem *intel_priv(struct pci_dev *pci)
 
 static int intel_i3c_init(struct mipi_i3c_hci_pci *hci)
 {
+	struct intel_host *host = devm_kzalloc(&hci->pci->dev, sizeof(*host), GFP_KERNEL);
 	void __iomem *priv = intel_priv(hci->pci);
 
-	if (!priv)
+	if (!host || !priv)
 		return -ENOMEM;
 
 	dma_set_mask_and_coherent(&hci->pci->dev, DMA_BIT_MASK(64));
 
+	hci->private = host;
+	host->priv = priv;
+
 	intel_reset(priv);
 
+	intel_ltr_expose(&hci->pci->dev);
+	intel_add_debugfs(hci);
+
 	return 0;
 }
 
+static void intel_i3c_exit(struct mipi_i3c_hci_pci *hci)
+{
+	intel_remove_debugfs(hci);
+	intel_ltr_hide(&hci->pci->dev);
+}
+
 static const struct mipi_i3c_hci_pci_info intel_info = {
 	.init = intel_i3c_init,
+	.exit = intel_i3c_exit,
 };
 
 static int mipi_i3c_hci_pci_probe(struct pci_dev *pci,