[PATCH v8 09/10] misc: amd-sbi: Add support for register xfer

Akshay Gupta
2025-04-11T13:32:20Z

- Provide user register access over IOCTL.
Both register read and write are supported.
- APML interface does not provide a synchronization method. By defining,
a register access path, we use APML modules and library for
all APML transactions. Without having to use external tools such as
i2c-tools, which may cause race conditions.

Reviewed-by: Naveen Krishna Chatradhi <naveenkrishna.chatradhi@amd.com>
Signed-off-by: Akshay Gupta <akshay.gupta@amd.com>
---
Changes since v7:
- Address Arnd comment:
- New IOCTL and structure defined to separate
ioctl for each protocol

Changes since v6:
- Rebased patch, previously patch 10

Changes since v5:
- Patch rebased

Changes since v4:
- Previously patch 8
- Address review comment for documentation warning

Changes since v3:
- Add ioctl description comment

Changes since v2:
- update the MACROS name as per feedback

Changes since v1:
- bifurcated from previous patch 5

drivers/misc/amd-sbi/rmi-core.c | 29 +++++++++++++++++++++++++++++
include/uapi/misc/amd-apml.h | 31 +++++++++++++++++++++++++++++++
2 files changed, 60 insertions(+)

diff --git a/drivers/misc/amd-sbi/rmi-core.c b/drivers/misc/amd-sbi/rmi-core.c
index 171d6e871373..b653a21a909e 100644
--- a/drivers/misc/amd-sbi/rmi-core.c
+++ b/drivers/misc/amd-sbi/rmi-core.c
@@ -350,6 +350,33 @@ int rmi_mailbox_xfer(struct sbrmi_data *data,
return ret;
}

+static int apml_rmi_reg_xfer(struct sbrmi_data *data,
+ struct apml_reg_xfer_msg __user *arg)
+{
+ struct apml_reg_xfer_msg msg = { 0 };
+ unsigned int data_read;
+ int ret;
+
+ /* Copy the structure from user */
+ if (copy_from_user(&msg, arg, sizeof(struct apml_reg_xfer_msg)))
+ return -EFAULT;
+
+ mutex_lock(&data->lock);
+ if (msg.rflag) {
+ ret = regmap_read(data->regmap, msg.reg_addr, &data_read);
+ if (!ret)
+ msg.data_in_out = data_read;
+ } else {
+ ret = regmap_write(data->regmap, msg.reg_addr, msg.data_in_out);
+ }
+
+ mutex_unlock(&data->lock);
+
+ if (msg.rflag && !ret)
+ return copy_to_user(arg, &msg, sizeof(struct apml_reg_xfer_msg));
+ return ret;
+}
+
static int apml_mailbox_xfer(struct sbrmi_data *data, struct apml_mbox_msg __user *arg)
{
struct apml_mbox_msg msg = { 0 };
@@ -414,6 +441,8 @@ static long sbrmi_ioctl(struct file *fp, unsigned int cmd, unsigned long arg)
return apml_cpuid_xfer(data, argp);
case SBRMI_IOCTL_MCAMSR_CMD:
return apml_mcamsr_xfer(data, argp);
+ case SBRMI_IOCTL_REG_XFER_CMD:
+ return apml_rmi_reg_xfer(data, argp);
default:
return -ENOTTY;
}
diff --git a/include/uapi/misc/amd-apml.h b/include/uapi/misc/amd-apml.h
index f718675d3966..3b5f5af61a1e 100644
--- a/include/uapi/misc/amd-apml.h
+++ b/include/uapi/misc/amd-apml.h
@@ -58,6 +58,21 @@ struct apml_mcamsr_msg {
__u32 pad;
};

+struct apml_reg_xfer_msg {
+ /*
+ * RMI register address offset
+ */
+ u16 reg_addr;
+ /*
+ * Register data for read/write
+ */
+ u8 data_in_out;
+ /*
+ * Register read or write
+ */
+ u8 rflag;
+};
+
/*
* AMD sideband interface base IOCTL
*/
@@ -118,4 +133,20 @@ struct apml_mcamsr_msg {
*/
#define SBRMI_IOCTL_MCAMSR_CMD _IOWR(SB_BASE_IOCTL_NR, 2, struct apml_mcamsr_msg)

+/**
+ * DOC: SBRMI_IOCTL_REG_XFER_CMD
+ *
+ * @Parameters
+ *
+ * @struct apml_reg_xfer_msg
+ * Pointer to the &struct apml_reg_xfer_msg that will contain the protocol
+ * information
+ *
+ * @Description
+ * IOCTL command for APML messages using generic _IOWR
+ * The IOCTL provides userspace access to AMD sideband register xfer protocol
+ * - Register xfer protocol to get/set hardware register for given offset
+ */
+#define SBRMI_IOCTL_REG_XFER_CMD _IOWR(SB_BASE_IOCTL_NR, 3, struct apml_reg_xfer_msg)
+
#endif /*_AMD_APML_H_*/
--
2.25.1