linux-kernel - [PATCH] bus: mhi: host: Update session id for each suspend and resume

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Message-Id: <20250912100827.294443-1-slark_xiao@163.com>
Date: Fri, 12 Sep 2025 18:08:27 +0800
From: Slark Xiao <slark_xiao@....com>
To: mani@...nel.org
Cc: mhi@...ts.linux.dev,
	linux-arm-msm@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Slark Xiao <slark_xiao@....com>
Subject: [PATCH] bus: mhi: host: Update session id for each suspend and resume

On Qualcomm module side, there is a UART print as below:
session id: 0x355fe689 state:2
session id: 0x1f478e42 state:5
The session id reads from register BHI_IMGTXDB(0x218), and the
state indicates the D3 or D0 state.

In Windows side, MHI driver would update this session id for each
suspend/resume progress. We benefit from this mechanism since it
could help sync each suspend and resume progress between host and
device, especially for some suspend issue which needs to take
hundreds or thousands cycle. We can easy to figure out which
suspend cycle get a problem and what's happened at that time for
both host and device because they have same id.

But in Linux side, this session id value would always be 0x0.
So we add it for potential debug usage.

Signed-off-by: Slark Xiao <slark_xiao@....com>
---
 drivers/bus/mhi/host/pm.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/drivers/bus/mhi/host/pm.c b/drivers/bus/mhi/host/pm.c
index 33d92bf2fc3e..a6573f687363 100644
--- a/drivers/bus/mhi/host/pm.c
+++ b/drivers/bus/mhi/host/pm.c
@@ -864,6 +864,13 @@ int mhi_pm_suspend(struct mhi_controller *mhi_cntrl)
 	struct device *dev = &mhi_cntrl->mhi_dev->dev;
 	enum mhi_pm_state new_state;
 	int ret;
+	void __iomem *base = mhi_cntrl->bhi;
+	u32 session_id;
+
+	session_id = MHI_RANDOM_U32_NONZERO(BHI_TXDB_SEQNUM_BMSK);
+	dev_dbg(dev, "Starting enter suspend, session id: 0x%x\n",
+		session_id);
+	mhi_write_reg(mhi_cntrl, base, BHI_IMGTXDB, session_id);

 	if (mhi_cntrl->pm_state == MHI_PM_DISABLE)
 		return -EINVAL;
@@ -952,6 +959,14 @@ static int __mhi_pm_resume(struct mhi_controller *mhi_cntrl, bool force)
 	struct device *dev = &mhi_cntrl->mhi_dev->dev;
 	enum mhi_pm_state cur_state;
 	int ret;
+	void __iomem *base = mhi_cntrl->bhi;
+	u32 session_id;
+
+	session_id = MHI_RANDOM_U32_NONZERO(BHI_TXDB_SEQNUM_BMSK);
+	dev_dbg(dev, "Starting enter resume, session id: 0x%x\n",
+		session_id);
+
+	mhi_write_reg(mhi_cntrl, base, BHI_IMGTXDB, session_id);

 	dev_dbg(dev, "Entered with PM state: %s, MHI state: %s\n",
 		to_mhi_pm_state_str(mhi_cntrl->pm_state),
-- 
2.25.1