linux-kernel - [PATCH] bus: sunxi-rsb: Return correct data when mixing 16-bit and 8-bit reads

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Date:   Wed, 19 Feb 2020 02:09:50 +0100
From:   Ondrej Jirman <megous@...ous.com>
To:     linux-sunxi@...glegroups.com
Cc:     Ondrej Jirman <megous@...ous.com>,
        Maxime Ripard <mripard@...nel.org>,
        Chen-Yu Tsai <wens@...e.org>,
        Samuel Holland <samuel@...lland.org>,
        Stephen Boyd <swboyd@...omium.org>,
        linux-arm-kernel@...ts.infradead.org (moderated list:ARM/Allwinner
        sunXi SoC support), linux-kernel@...r.kernel.org (open list)
Subject: [PATCH] bus: sunxi-rsb: Return correct data when mixing 16-bit and 8-bit reads

When doing a 16-bit read that returns data in the MSB byte, the
RSB_DATA register will keep the MSB byte unchanged when doing
the following 8-bit read. sunxi_rsb_read() will then return
a result that contains high byte from 16-bit read mixed with
the 8-bit result.

The consequence is that after this happens the PMIC's regmap will
look like this: (0x33 is the high byte from the 16-bit read)

% cat /sys/kernel/debug/regmap/sunxi-rsb-3a3/registers
00: 33
01: 33
02: 33
03: 33
04: 33
05: 33
06: 33
07: 33
08: 33
09: 33
0a: 33
0b: 33
0c: 33
0d: 33
0e: 33
[snip]

Fix this by masking the result of the read with the correct mask
based on the size of the read. There are no 16-bit users in the
mainline kernel, so this doesn't need to get into the stable tree.

Signed-off-by: Ondrej Jirman <megous@...ous.com>
---
 drivers/bus/sunxi-rsb.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/bus/sunxi-rsb.c b/drivers/bus/sunxi-rsb.c
index b8043b58568ac..8ab6a3865f569 100644
--- a/drivers/bus/sunxi-rsb.c
+++ b/drivers/bus/sunxi-rsb.c
@@ -316,6 +316,7 @@ static int sunxi_rsb_read(struct sunxi_rsb *rsb, u8 rtaddr, u8 addr,
 {
 	u32 cmd;
 	int ret;
+	u32 mask;
 
 	if (!buf)
 		return -EINVAL;
@@ -323,12 +324,15 @@ static int sunxi_rsb_read(struct sunxi_rsb *rsb, u8 rtaddr, u8 addr,
 	switch (len) {
 	case 1:
 		cmd = RSB_CMD_RD8;
+		mask = 0xffu;
 		break;
 	case 2:
 		cmd = RSB_CMD_RD16;
+		mask = 0xffffu;
 		break;
 	case 4:
 		cmd = RSB_CMD_RD32;
+		mask = 0xffffffffu;
 		break;
 	default:
 		dev_err(rsb->dev, "Invalid access width: %zd\n", len);
@@ -345,7 +349,7 @@ static int sunxi_rsb_read(struct sunxi_rsb *rsb, u8 rtaddr, u8 addr,
 	if (ret)
 		goto unlock;
 
-	*buf = readl(rsb->regs + RSB_DATA);
+	*buf = readl(rsb->regs + RSB_DATA) & mask;
 
 unlock:
 	mutex_unlock(&rsb->lock);
-- 
2.25.1