[PATCH 2/2] ipmi: ssif_bmc: add GPIO-based alert mechanism

[Potin Lai <potin.lai.pt@xxxxxxxxx>]

From: Cosmo Chou <chou.cosmo@xxxxxxxxx>

Implement GPIO-based alert mechanism in the SSIF BMC driver to notify
the host when a response is ready.

This improves host-BMC communication efficiency by providing immediate
notification, potentially reducing host polling overhead.

Signed-off-by: Cosmo Chou <chou.cosmo@xxxxxxxxx>
---
 drivers/char/ipmi/ssif_bmc.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/drivers/char/ipmi/ssif_bmc.c b/drivers/char/ipmi/ssif_bmc.c
index a14fafc583d4..73be166b0042 100644
--- a/drivers/char/ipmi/ssif_bmc.c
+++ b/drivers/char/ipmi/ssif_bmc.c
@@ -17,6 +17,7 @@
 #include <linux/spinlock.h>
 #include <linux/timer.h>
 #include <linux/jiffies.h>
+#include <linux/gpio/consumer.h>
 #include <linux/ipmi_ssif_bmc.h>
 
 #define DEVICE_NAME                             "ipmi-ssif-host"
@@ -102,6 +103,7 @@ struct ssif_bmc_ctx {
 	struct ssif_part_buffer part_buf;
 	struct ipmi_ssif_msg    response;
 	struct ipmi_ssif_msg    request;
+	struct gpio_desc        *alert;
 };
 
 static inline struct ssif_bmc_ctx *to_ssif_bmc(struct file *file)
@@ -222,6 +224,9 @@ static ssize_t ssif_bmc_write(struct file *file, const char __user *buf, size_t
 
 	/* Clean old request buffer */
 	memset(&ssif_bmc->request, 0, sizeof(struct ipmi_ssif_msg));
+
+	if (!IS_ERR(ssif_bmc->alert))
+		gpiod_set_value(ssif_bmc->alert, 1);
 exit:
 	spin_unlock_irqrestore(&ssif_bmc->lock, flags);
 
@@ -584,6 +589,9 @@ static void process_smbus_cmd(struct ssif_bmc_ctx *ssif_bmc, u8 *val)
 	memset(&ssif_bmc->part_buf.payload[0], 0, MAX_PAYLOAD_PER_TRANSACTION);
 
 	if (*val == SSIF_IPMI_SINGLEPART_WRITE || *val == SSIF_IPMI_MULTIPART_WRITE_START) {
+		if (!IS_ERR(ssif_bmc->alert))
+			gpiod_set_value(ssif_bmc->alert, 0);
+
 		/*
 		 * The response maybe not come in-time, causing host SSIF driver
 		 * to timeout and resend a new request. In such case check for
@@ -640,6 +648,8 @@ static void on_read_requested_event(struct ssif_bmc_ctx *ssif_bmc, u8 *val)
 	calculate_response_part_pec(&ssif_bmc->part_buf);
 	ssif_bmc->part_buf.index = 0;
 	*val = ssif_bmc->part_buf.length;
+	if (!IS_ERR(ssif_bmc->alert))
+		gpiod_set_value(ssif_bmc->alert, 0);
 }
 
 static void on_read_processed_event(struct ssif_bmc_ctx *ssif_bmc, u8 *val)
@@ -808,6 +818,11 @@ static int ssif_bmc_probe(struct i2c_client *client)
 	if (!ssif_bmc)
 		return -ENOMEM;
 
+	/* Request GPIO for alerting the host that response is ready */
+	ssif_bmc->alert = devm_gpiod_get(&client->dev, "alert", GPIOD_ASIS);
+	if (!IS_ERR(ssif_bmc->alert))
+		gpiod_direction_output(ssif_bmc->alert, 0);
+
 	spin_lock_init(&ssif_bmc->lock);
 
 	init_waitqueue_head(&ssif_bmc->wait_queue);

-- 
2.31.1