linux-kernel - [PATCH v4 03/11] bus: mhi: host: Add support to read MHI capabilities

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Message-Id: <20250609-mhi_bw_up-v4-3-3faa8fe92b05@qti.qualcomm.com>
Date: Mon, 09 Jun 2025 16:21:24 +0530
From: Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>
To: Bjorn Helgaas <bhelgaas@...gle.com>,
        Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
        Jingoo Han <jingoohan1@...il.com>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Rob Herring <robh@...nel.org>, Jeff Johnson <jjohnson@...nel.org>,
        Bartosz Golaszewski <brgl@...ev.pl>,
        Manivannan Sadhasivam <mani@...nel.org>,
        Krzysztof Wilczyński <kwilczynski@...nel.org>,
        Manivannan Sadhasivam <mani@...nel.org>,
        Krzysztof Wilczyński <kwilczynski@...nel.org>
Cc: linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, mhi@...ts.linux.dev,
        linux-wireless@...r.kernel.org, ath11k@...ts.infradead.org,
        qiang.yu@....qualcomm.com, quic_vbadigan@...cinc.com,
        quic_vpernami@...cinc.com, quic_mrana@...cinc.com,
        Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>,
        Jeff Johnson <jeff.johnson@....qualcomm.com>
Subject: [PATCH v4 03/11] bus: mhi: host: Add support to read MHI
 capabilities

From: Vivek Pernamitta <quic_vpernami@...cinc.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 <quic_vpernami@...cinc.com>
Signed-off-by: Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>
---
 drivers/bus/mhi/common.h    | 13 +++++++++++++
 drivers/bus/mhi/host/init.c | 34 ++++++++++++++++++++++++++++++++++
 2 files changed, 47 insertions(+)

diff --git a/drivers/bus/mhi/common.h b/drivers/bus/mhi/common.h
index dda340aaed95a5573a2ec776ca712e11a1ed0b52..58f27c6ba63e3e6fa28ca48d6d1065684ed6e1dd 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 13e7a55f54ff45b83b3f18b97e2cdd83d4836fe3..9102ce13a2059f599b46d25ef631f643142642be 100644
--- a/drivers/bus/mhi/host/init.c
+++ b/drivers/bus/mhi/host/init.c
@@ -467,6 +467,40 @@ 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;
+
+	*offset = (__force u32)le32_to_cpu(*offset);
+	do {
+		if (*offset >= mhi_cntrl->reg_len)
+			return -ENXIO;
+
+		ret = mhi_read_reg(mhi_cntrl, mhi_cntrl->regs, *offset, &val);
+		if (ret)
+			return ret;
+
+		val = (__force u32)le32_to_cpu(val);
+		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