[PATCH v2 2/3] nvmem: mtk-efuse: add support for 32-bit aligned reads

[Roman Vivchar via B4 Relay <devnull+rva333.protonmail.com@kernel.org>]

From: Roman Vivchar <rva333@protonmail.com>

Some MediaTek SoCs, such as mt6572, don't support 8-bit reads, leading
to zeroes or garbage data. 32-bit aligned reads must be used instead.

Introduce a 'mtk_reg_read_aligned' helper to enforce 32-bit aligned
register access. All reads will be performed by reading 4-byte words
and masking them.

Signed-off-by: Roman Vivchar <rva333@protonmail.com>
---
 drivers/nvmem/mtk-efuse.c | 35 ++++++++++++++++++++++++++++++++++-
 1 file changed, 34 insertions(+), 1 deletion(-)

diff --git a/drivers/nvmem/mtk-efuse.c b/drivers/nvmem/mtk-efuse.c
index af953e1d9230..178b9d85f813 100644
--- a/drivers/nvmem/mtk-efuse.c
+++ b/drivers/nvmem/mtk-efuse.c
@@ -4,6 +4,7 @@
  * Author: Andrew-CT Chen <andrew-ct.chen@mediatek.com>
  */
 
+#include <linux/align.h>
 #include <linux/device.h>
 #include <linux/module.h>
 #include <linux/mod_devicetable.h>
@@ -14,12 +15,37 @@
 
 struct mtk_efuse_pdata {
 	bool uses_post_processing;
+	bool needs_aligned_read;
 };
 
 struct mtk_efuse_priv {
 	void __iomem *base;
 };
 
+static int mtk_reg_read_aligned(void *context,
+				unsigned int reg, void *_val, size_t bytes)
+{
+	struct mtk_efuse_priv *priv = context;
+	u8 *val = _val;
+	u32 i, pos, shift, val32;
+
+	for (i = 0; i < bytes; i++, val++) {
+		pos = reg + i;
+
+		/*
+		 * Read on 32-bit word boundary or if it's the first
+		 * iteration
+		 */
+		if (i == 0 || IS_ALIGNED(pos, 4))
+			val32 = readl(priv->base + (pos & ~3));
+
+		shift = (pos & 3) * 8;
+		*val = (val32 >> shift) & 0xff;
+	}
+
+	return 0;
+}
+
 static int mtk_reg_read(void *context,
 			unsigned int reg, void *_val, size_t bytes)
 {
@@ -82,7 +108,12 @@ static int mtk_efuse_probe(struct platform_device *pdev)
 	econfig.add_legacy_fixed_of_cells = true;
 	econfig.stride = 1;
 	econfig.word_size = 1;
-	econfig.reg_read = mtk_reg_read;
+
+	if (pdata->needs_aligned_read)
+		econfig.reg_read = mtk_reg_read_aligned;
+	else
+		econfig.reg_read = mtk_reg_read;
+
 	econfig.size = resource_size(res);
 	econfig.priv = priv;
 	econfig.dev = dev;
@@ -103,10 +134,12 @@ static int mtk_efuse_probe(struct platform_device *pdev)
 
 static const struct mtk_efuse_pdata mtk_mt8186_efuse_pdata = {
 	.uses_post_processing = true,
+	.needs_aligned_read = false,
 };
 
 static const struct mtk_efuse_pdata mtk_efuse_pdata = {
 	.uses_post_processing = false,
+	.needs_aligned_read = false,
 };
 
 static const struct of_device_id mtk_efuse_of_match[] = {

-- 
2.54.0