[PATCH 6.18.y 2/2] hwmon: (powerz) Avoid cacheline sharing for DMA buffer

[Sasha Levin <sashal@kernel.org>]

From: Thomas Weißschuh <linux@weissschuh.net>

[ Upstream commit 3023c050af3600bf451153335dea5e073c9a3088 ]

Depending on the architecture the transfer buffer may share a cacheline
with the following mutex. As the buffer may be used for DMA, that is
problematic.

Use the high-level DMA helpers to make sure that cacheline sharing can
not happen.

Also drop the comment, as the helpers are documentation enough.

https://sashiko.dev/#/message/20260408175814.934BFC19421%40smtp.kernel.org

Fixes: 4381a36abdf1c ("hwmon: add POWER-Z driver")
Cc: stable@vger.kernel.org # ca085faabb42: dma-mapping: add __dma_from_device_group_begin()/end()
Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Link: https://lore.kernel.org/r/20260408-powerz-cacheline-alias-v1-1-1254891be0dd@weissschuh.net
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/hwmon/powerz.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/hwmon/powerz.c b/drivers/hwmon/powerz.c
index a75b941bd6e2f..dbe6b7ee16446 100644
--- a/drivers/hwmon/powerz.c
+++ b/drivers/hwmon/powerz.c
@@ -6,6 +6,7 @@
 
 #include <linux/completion.h>
 #include <linux/device.h>
+#include <linux/dma-mapping.h>
 #include <linux/hwmon.h>
 #include <linux/module.h>
 #include <linux/mutex.h>
@@ -33,7 +34,9 @@ struct powerz_sensor_data {
 } __packed;
 
 struct powerz_priv {
-	char transfer_buffer[64];	/* first member to satisfy DMA alignment */
+	__dma_from_device_group_begin();
+	char transfer_buffer[64];
+	__dma_from_device_group_end();
 	struct mutex mutex;
 	struct completion completion;
 	struct urb *urb;
-- 
2.53.0