[PATCH v2 1/6] bus: mhi: host: Add support to read MHI capabilities

Krishna Chaitanya Chundru
2026-04-11T08:12:17Z

From: Vivek Pernamitta <vivek.pernamitta@oss.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@oss.qualcomm.com>
Signed-off-by: Sivareddy Surasani <sivareddy.surasani@oss.qualcomm.com>
Signed-off-by: Krishna Chaitanya Chundru <krishna.chundru@oss.qualcomm.com>
---
drivers/bus/mhi/common.h | 11 +++++++++++
drivers/bus/mhi/host/init.c | 32 ++++++++++++++++++++++++++++++++
2 files changed, 43 insertions(+)

diff --git a/drivers/bus/mhi/common.h b/drivers/bus/mhi/common.h
index dda340aaed95a5573a2ec776ca712e11a1ed0b52..4c316f3d5a68beb01f15cf575b03747096fdcf2c 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 +208,13 @@
#define MHI_RSCTRE_DATA_DWORD1 cpu_to_le32(FIELD_PREP(GENMASK(23, 16), \
MHI_PKT_TYPE_COALESCING))

+#define MHI_CAP_ID_INTX 0x1
+#define MHI_CAP_ID_TIME_SYNC 0x2
+#define MHI_CAP_ID_BW_SCALE 0x3
+#define MHI_CAP_ID_TSC_TIME_SYNC 0x4
+#define MHI_CAP_ID_MAX_TRB_LEN 0x5
+#define MHI_CAP_ID_MAX 0x6
+
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 0a728ca2c494836b0e0ce4c3f4aea41794c0868b..c2162aa04e810e45ccfbedd20aaa62f892420d31 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 val, cur_cap, next_offset, cur_offset;
+ int ret;
+
+ /* Get the first supported capability offset */
+ ret = mhi_read_reg_field(mhi_cntrl, mhi_cntrl->regs, MISCOFF, MISC_CAP_MASK, &cur_offset);
+ if (ret)
+ return 0;
+
+ do {
+ if (cur_offset >= mhi_cntrl->reg_len)
+ return 0;
+
+ ret = mhi_read_reg(mhi_cntrl, mhi_cntrl->regs, cur_offset, &val);
+ if (ret)
+ return 0;
+
+ 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 0;
+
+ if (cur_cap == capability)
+ return cur_offset;
+
+ cur_offset = next_offset;
+ } while (next_offset);
+
+ return 0;
+}
+
int mhi_init_mmio(struct mhi_controller *mhi_cntrl)
{
u32 val;

--
2.34.1