bus: mhi: core: Add device hardware reset support

The MHI specification allows to perform a hard reset of the device
when writing to the SOC_RESET register. It can be used to completely
restart the device (e.g. in case of unrecoverable MHI error).

This is up to the MHI controller driver to determine when this hard
reset should be used, and in case of MHI errors, should be used as
a reset of last resort (after standard MHI stack reset).

This function is a stateless function, the MHI layer do nothing except
triggering the reset by writing into the right register(s), this is up
to the caller to ensure right mhi_controller state (e.g. unregister the
controller if necessary).
Signed-off-by: Loic Poulain <loic.poulain@linaro.org>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>

drivers/bus/mhi/core/main.c

@@ -135,6 +135,19 @@ enum mhi_state mhi_get_mhi_state(struct mhi_controller *mhi_cntrl)
 }
 EXPORT_SYMBOL_GPL(mhi_get_mhi_state);
 
+void mhi_soc_reset(struct mhi_controller *mhi_cntrl)
+{
+	if (mhi_cntrl->reset) {
+		mhi_cntrl->reset(mhi_cntrl);
+		return;
+	}
+
+	/* Generic MHI SoC reset */
+	mhi_write_reg(mhi_cntrl, mhi_cntrl->regs, MHI_SOC_RESET_REQ_OFFSET,
+		      MHI_SOC_RESET_REQ);
+}
+EXPORT_SYMBOL_GPL(mhi_soc_reset);
+
 int mhi_map_single_no_bb(struct mhi_controller *mhi_cntrl,
 			 struct mhi_buf_info *buf_info)
 {

include/linux/mhi.h

@@ -347,6 +347,7 @@ struct mhi_controller_config {
  * @unmap_single: CB function to destroy TRE buffer
  * @read_reg: Read a MHI register via the physical link (required)
  * @write_reg: Write a MHI register via the physical link (required)
+ * @reset: Controller specific reset function (optional)
  * @buffer_len: Bounce buffer length
  * @index: Index of the MHI controller instance
  * @bounce_buf: Use of bounce buffer
@@ -437,6 +438,7 @@ struct mhi_controller {
 			u32 *out);
 	void (*write_reg)(struct mhi_controller *mhi_cntrl, void __iomem *addr,
 			  u32 val);
+	void (*reset)(struct mhi_controller *mhi_cntrl);
 
 	size_t buffer_len;
 	int index;
@@ -672,6 +674,13 @@ enum mhi_ee_type mhi_get_exec_env(struct mhi_controller *mhi_cntrl);
  */
 enum mhi_state mhi_get_mhi_state(struct mhi_controller *mhi_cntrl);
 
+/**
+ * mhi_soc_reset - Trigger a device reset. This can be used as a last resort
+ *		   to reset and recover a device.
+ * @mhi_cntrl: MHI controller
+ */
+void mhi_soc_reset(struct mhi_controller *mhi_cntrl);
+
 /**
  * mhi_device_get - Disable device low power mode
  * @mhi_dev: Device associated with the channel