linux-kernel - [PATCH] spi: spidev: Align buffers for DMA

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Message-ID: <20200728100832.24788-1-ceggers@arri.de>
Date:   Tue, 28 Jul 2020 12:08:32 +0200
From:   Christian Eggers <ceggers@...i.de>
To:     Mark Brown <broonie@...nel.org>
CC:     <linux-spi@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        "Christian Eggers" <ceggers@...i.de>, <stable@...r.kernel.org>
Subject: [PATCH] spi: spidev: Align buffers for DMA

Simply copying all xfers from userspace into one bounce buffer causes
alignment problems if the SPI controller uses DMA.

Ensure that all transfer data blocks within the rx and tx bounce buffers
are aligned for DMA (according to ARCH_KMALLOC_MINALIGN).

Alignment may increase the usage of the bounce buffers. In some cases,
the buffers may need to be increased using the "bufsiz" module
parameter.

Signed-off-by: Christian Eggers <ceggers@...i.de>
Cc: stable@...r.kernel.org
---
 drivers/spi/spidev.c | 21 +++++++++++++--------
 1 file changed, 13 insertions(+), 8 deletions(-)

diff --git a/drivers/spi/spidev.c b/drivers/spi/spidev.c
index 59e07675ef86..455e99c4958e 100644
--- a/drivers/spi/spidev.c
+++ b/drivers/spi/spidev.c
@@ -224,6 +224,11 @@ static int spidev_message(struct spidev_data *spidev,
 	for (n = n_xfers, k_tmp = k_xfers, u_tmp = u_xfers;
 			n;
 			n--, k_tmp++, u_tmp++) {
+		/* Ensure that also following allocations from rx_buf/tx_buf will meet
+		 * DMA alignment requirements.
+		 */
+		unsigned int len_aligned = ALIGN(u_tmp->len, ARCH_KMALLOC_MINALIGN);
+
 		k_tmp->len = u_tmp->len;
 
 		total += k_tmp->len;
@@ -239,17 +244,17 @@ static int spidev_message(struct spidev_data *spidev,
 
 		if (u_tmp->rx_buf) {
 			/* this transfer needs space in RX bounce buffer */
-			rx_total += k_tmp->len;
+			rx_total += len_aligned;
 			if (rx_total > bufsiz) {
 				status = -EMSGSIZE;
 				goto done;
 			}
 			k_tmp->rx_buf = rx_buf;
-			rx_buf += k_tmp->len;
+			rx_buf += len_aligned;
 		}
 		if (u_tmp->tx_buf) {
 			/* this transfer needs space in TX bounce buffer */
-			tx_total += k_tmp->len;
+			tx_total += len_aligned;
 			if (tx_total > bufsiz) {
 				status = -EMSGSIZE;
 				goto done;
@@ -259,7 +264,7 @@ static int spidev_message(struct spidev_data *spidev,
 						(uintptr_t) u_tmp->tx_buf,
 					u_tmp->len))
 				goto done;
-			tx_buf += k_tmp->len;
+			tx_buf += len_aligned;
 		}
 
 		k_tmp->cs_change = !!u_tmp->cs_change;
@@ -293,16 +298,16 @@ static int spidev_message(struct spidev_data *spidev,
 		goto done;
 
 	/* copy any rx data out of bounce buffer */
-	rx_buf = spidev->rx_buffer;
-	for (n = n_xfers, u_tmp = u_xfers; n; n--, u_tmp++) {
+	for (n = n_xfers, k_tmp = k_xfers, u_tmp = u_xfers;
+			n;
+			n--, k_tmp++, u_tmp++) {
 		if (u_tmp->rx_buf) {
 			if (copy_to_user((u8 __user *)
-					(uintptr_t) u_tmp->rx_buf, rx_buf,
+					(uintptr_t) u_tmp->rx_buf, k_tmp->rx_buf,
 					u_tmp->len)) {
 				status = -EFAULT;
 				goto done;
 			}
-			rx_buf += u_tmp->len;
 		}
 	}
 	status = total;
-- 
Christian Eggers
Embedded software developer

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