linux-kernel - [PATCH 01/11] bus: mhi: host: Add support to read MHI capabilities

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Message-Id: <20251211-siva_mhi_dp2-v1-1-d2895c4ec73a@oss.qualcomm.com>
Date: Thu, 11 Dec 2025 13:37:33 +0530
From: Sivareddy Surasani <sivareddy.surasani@....qualcomm.com>
To: Manivannan Sadhasivam <mani@...nel.org>, Jonathan Corbet <corbet@....net>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: mhi@...ts.linux.dev, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
        Upal Kumar Saha <upal.saha@....qualcomm.com>,
        Himanshu Shukla <quic_himashuk@...cinc.com>,
        Sivareddy Surasani <sivareddy.surasani@....qualcomm.com>,
        Vivek Pernamitta <vivek.pernamitta@....qualcomm.com>,
        Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>
Subject: [PATCH 01/11] bus: mhi: host: Add support to read MHI capabilities

From: Vivek Pernamitta <vivek.pernamitta@....qualcomm.com>

As per MHI spec v1.2,sec 6.6, MHI has capability registers which are
located after the ERDB array. The location of this group of registers is
indicated by the MISCOFF register. Each capability has a capability ID to
determine which functionality is supported and each capability will point
to the next capability supported.

Add a basic function to read those capabilities offsets.

Signed-off-by: Vivek Pernamitta <vivek.pernamitta@....qualcomm.com>
Signed-off-by: Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>
Signed-off-by: Sivareddy Surasani <sivareddy.surasani@....qualcomm.com>
---
 drivers/bus/mhi/common.h    | 13 +++++++++++++
 drivers/bus/mhi/host/init.c | 32 ++++++++++++++++++++++++++++++++
 2 files changed, 45 insertions(+)

diff --git a/drivers/bus/mhi/common.h b/drivers/bus/mhi/common.h
index dda340aaed95..58f27c6ba63e 100644
--- a/drivers/bus/mhi/common.h
+++ b/drivers/bus/mhi/common.h
@@ -16,6 +16,7 @@
 #define MHICFG				0x10
 #define CHDBOFF				0x18
 #define ERDBOFF				0x20
+#define MISCOFF				0x24
 #define BHIOFF				0x28
 #define BHIEOFF				0x2c
 #define DEBUGOFF			0x30
@@ -113,6 +114,9 @@
 #define MHISTATUS_MHISTATE_MASK		GENMASK(15, 8)
 #define MHISTATUS_SYSERR_MASK		BIT(2)
 #define MHISTATUS_READY_MASK		BIT(0)
+#define MISC_CAP_MASK			GENMASK(31, 0)
+#define CAP_CAPID_MASK			GENMASK(31, 24)
+#define CAP_NEXT_CAP_MASK		GENMASK(23, 12)
 
 /* Command Ring Element macros */
 /* No operation command */
@@ -204,6 +208,15 @@
 #define MHI_RSCTRE_DATA_DWORD1		cpu_to_le32(FIELD_PREP(GENMASK(23, 16), \
 							       MHI_PKT_TYPE_COALESCING))
 
+enum mhi_capability_type {
+	MHI_CAP_ID_INTX = 0x1,
+	MHI_CAP_ID_TIME_SYNC = 0x2,
+	MHI_CAP_ID_BW_SCALE = 0x3,
+	MHI_CAP_ID_TSC_TIME_SYNC = 0x4,
+	MHI_CAP_ID_MAX_TRB_LEN = 0x5,
+	MHI_CAP_ID_MAX,
+};
+
 enum mhi_pkt_type {
 	MHI_PKT_TYPE_INVALID = 0x0,
 	MHI_PKT_TYPE_NOOP_CMD = 0x1,
diff --git a/drivers/bus/mhi/host/init.c b/drivers/bus/mhi/host/init.c
index 099be8dd1900..4c092490c9fd 100644
--- a/drivers/bus/mhi/host/init.c
+++ b/drivers/bus/mhi/host/init.c
@@ -466,6 +466,38 @@ static int mhi_init_dev_ctxt(struct mhi_controller *mhi_cntrl)
 	return ret;
 }
 
+static int mhi_find_capability(struct mhi_controller *mhi_cntrl, u32 capability, u32 *offset)
+{
+	u32 val, cur_cap, next_offset;
+	int ret;
+
+	/* Get the first supported capability offset */
+	ret = mhi_read_reg_field(mhi_cntrl, mhi_cntrl->regs, MISCOFF, MISC_CAP_MASK, offset);
+	if (ret)
+		return ret;
+
+	do {
+		if (*offset >= mhi_cntrl->reg_len)
+			return -ENXIO;
+
+		ret = mhi_read_reg(mhi_cntrl, mhi_cntrl->regs, *offset, &val);
+		if (ret)
+			return ret;
+
+		cur_cap = FIELD_GET(CAP_CAPID_MASK, val);
+		next_offset = FIELD_GET(CAP_NEXT_CAP_MASK, val);
+		if (cur_cap >= MHI_CAP_ID_MAX)
+			return -ENXIO;
+
+		if (cur_cap == capability)
+			return 0;
+
+		*offset = next_offset;
+	} while (next_offset);
+
+	return -ENXIO;
+}
+
 int mhi_init_mmio(struct mhi_controller *mhi_cntrl)
 {
 	u32 val;

-- 
2.34.1