linux-kernel - [PATCH 1/2] spi: fsi: Fix spurious timeout

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Date:   Wed, 25 May 2022 11:58:51 -0500
From:   Eddie James <eajames@...ux.ibm.com>
To:     broonie@...nel.org
Cc:     linux-spi@...r.kernel.org, linux-kernel@...r.kernel.org,
        Eddie James <eajames@...ux.ibm.com>
Subject: [PATCH 1/2] spi: fsi: Fix spurious timeout

The driver may return a timeout error even if the status register
indicates that the transfer may proceed. Fix this by restructuring
the polling loop.

Fixes: 89b35e3f2851 ("spi: fsi: Implement a timeout for polling status")
Signed-off-by: Eddie James <eajames@...ux.ibm.com>
---
 I have one concern still, that if the kernel is very busy, it may
 schedule other work for the entire timeout period between assigning
 "end" and checking if timed out in the do/while loop... Is it worth
 worrying about this case?

 drivers/spi/spi-fsi.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/drivers/spi/spi-fsi.c b/drivers/spi/spi-fsi.c
index d403a7a3021d..72ab066ce552 100644
--- a/drivers/spi/spi-fsi.c
+++ b/drivers/spi/spi-fsi.c
@@ -319,12 +319,12 @@ static int fsi_spi_transfer_data(struct fsi_spi *ctx,
 
 			end = jiffies + msecs_to_jiffies(SPI_FSI_STATUS_TIMEOUT_MS);
 			do {
+				if (time_after(jiffies, end))
+					return -ETIMEDOUT;
+
 				rc = fsi_spi_status(ctx, &status, "TX");
 				if (rc)
 					return rc;
-
-				if (time_after(jiffies, end))
-					return -ETIMEDOUT;
 			} while (status & SPI_FSI_STATUS_TDR_FULL);
 
 			sent += nb;
@@ -337,12 +337,12 @@ static int fsi_spi_transfer_data(struct fsi_spi *ctx,
 		while (transfer->len > recv) {
 			end = jiffies + msecs_to_jiffies(SPI_FSI_STATUS_TIMEOUT_MS);
 			do {
+				if (time_after(jiffies, end))
+					return -ETIMEDOUT;
+
 				rc = fsi_spi_status(ctx, &status, "RX");
 				if (rc)
 					return rc;
-
-				if (time_after(jiffies, end))
-					return -ETIMEDOUT;
 			} while (!(status & SPI_FSI_STATUS_RDR_FULL));
 
 			rc = fsi_spi_read_reg(ctx, SPI_FSI_DATA_RX, &in);
-- 
2.27.0