[PATCH 6.6.y] PCI: epf-mhi: Return 0, not remaining timeout, when eDMA ops complete

[Sasha Levin <sashal@kernel.org>]

From: Daniel Hodges <git@danielhodges.dev>

[ Upstream commit 36bfc3642b19a98f1302aed4437c331df9b481f0 ]

pci_epf_mhi_edma_read() and pci_epf_mhi_edma_write() start DMA
operations and wait for completion with a timeout.

On successful completion, they previously returned the remaining
timeout, which callers may treat as an error.  In particular,
mhi_ep_ring_add_element(), which calls pci_epf_mhi_edma_write() via
mhi_cntrl->write_sync(), interprets any non-zero return value as
failure.

Return 0 on success instead of the remaining timeout to prevent
mhi_ep_ring_add_element() from treating successful completion as an
error.

Fixes: 7b99aaaddabb ("PCI: epf-mhi: Add eDMA support")
Signed-off-by: Daniel Hodges <git@danielhodges.dev>
[mani: changed commit log as per https://lore.kernel.org/linux-pci/20260227191510.GA3904799@bhelgaas]
Signed-off-by: Manivannan Sadhasivam <mani@kernel.org>
Reviewed-by: Krishna Chaitanya Chundru <krishna.chundru@oss.qualcomm.com>
Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20260206200529.10784-1-git@danielhodges.dev
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/pci/endpoint/functions/pci-epf-mhi.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/pci/endpoint/functions/pci-epf-mhi.c b/drivers/pci/endpoint/functions/pci-epf-mhi.c
index 87154992ea11b..e5a7d1735649a 100644
--- a/drivers/pci/endpoint/functions/pci-epf-mhi.c
+++ b/drivers/pci/endpoint/functions/pci-epf-mhi.c
@@ -331,6 +331,8 @@ static int pci_epf_mhi_edma_read(struct mhi_ep_cntrl *mhi_cntrl,
 		dev_err(dev, "DMA transfer timeout\n");
 		dmaengine_terminate_sync(chan);
 		ret = -ETIMEDOUT;
+	} else {
+		ret = 0;
 	}
 
 err_unmap:
@@ -402,6 +404,8 @@ static int pci_epf_mhi_edma_write(struct mhi_ep_cntrl *mhi_cntrl,
 		dev_err(dev, "DMA transfer timeout\n");
 		dmaengine_terminate_sync(chan);
 		ret = -ETIMEDOUT;
+	} else {
+		ret = 0;
 	}
 
 err_unmap:
-- 
2.53.0