[PATCH] bus: mhi: host: Flush the posted write after writing to MHI_SOC_RESET_REQ_OFFSET

[Manivannan Sadhasivam]

mhi_soc_reset() tries to reset the device by writing to the
MHI_SOC_RESET_REQ_OFFSET register. But it doesn't do a read-back to ensure
that the write gets flushed to the device before returning to the caller.

This may lead to the delay (if implemented) on the caller to be
insufficient, if the posted write doesn't reach the device before the
delay.

So add a read-back after writing to the MHI_SOC_RESET_REQ_OFFSET register.

Fixes: b5a8d233a588 ("bus: mhi: core: Add device hardware reset support")
Reported-by: Alex Williamson <alex@xxxxxxxxxxx>
Closes: https://lore.kernel.org/linux-pci/20260622160822.09350246@xxxxxxxxxxx
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@xxxxxxxxxxxxxxxx>
---
 drivers/bus/mhi/host/main.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/bus/mhi/host/main.c b/drivers/bus/mhi/host/main.c
index 53c0ffe30070..4d458396233a 100644
--- a/drivers/bus/mhi/host/main.c
+++ b/drivers/bus/mhi/host/main.c
@@ -170,6 +170,9 @@ EXPORT_SYMBOL_GPL(mhi_get_mhi_state);
 
 void mhi_soc_reset(struct mhi_controller *mhi_cntrl)
 {
+	int __maybe_unused ret;
+	u32 tmp;
+
 	if (mhi_cntrl->reset) {
 		mhi_cntrl->reset(mhi_cntrl);
 		return;
@@ -178,6 +181,9 @@ void mhi_soc_reset(struct mhi_controller *mhi_cntrl)
 	/* Generic MHI SoC reset */
 	mhi_write_reg(mhi_cntrl, mhi_cntrl->regs, MHI_SOC_RESET_REQ_OFFSET,
 		      MHI_SOC_RESET_REQ);
+	/* Flush the posted write to the device (ignore return value) */
+	ret = mhi_read_reg(mhi_cntrl, mhi_cntrl->regs, MHI_SOC_RESET_REQ_OFFSET,
+			   &tmp);
 }
 EXPORT_SYMBOL_GPL(mhi_soc_reset);
 
-- 
2.43.0