nvmem: sunxi-sid: fix H3 SID controller support

It seems that doing some operation will make the value pre-read on H3
SID controller wrong again, so all operation should be performed by
register.

Change the SID reading to use register only.
Signed-off-by: Icenowy Zheng <icenowy@aosc.io>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/nvmem/sunxi_sid.c

@@ -85,13 +85,14 @@ static int sunxi_sid_read(void *context, unsigned int offset,
 }
 
 static int sun8i_sid_register_readout(const struct sunxi_sid *sid,
-				      const unsigned int word)
+				      const unsigned int offset,
+				      u32 *out)
 {
 	u32 reg_val;
 	int ret;
 
 	/* Set word, lock access, and set read command */
-	reg_val = (word & SUN8I_SID_OFFSET_MASK)
+	reg_val = (offset & SUN8I_SID_OFFSET_MASK)
 		  << SUN8I_SID_OFFSET_SHIFT;
 	reg_val |= SUN8I_SID_OP_LOCK | SUN8I_SID_READ;
 	writel(reg_val, sid->base + SUN8I_SID_PRCTL);
@@ -101,7 +102,49 @@ static int sun8i_sid_register_readout(const struct sunxi_sid *sid,
 	if (ret)
 		return ret;
 
+	if (out)
+		*out = readl(sid->base + SUN8I_SID_RDKEY);
+
 	writel(0, sid->base + SUN8I_SID_PRCTL);
+
+	return 0;
+}
+
+/*
+ * On Allwinner H3, the value on the 0x200 offset of the SID controller seems
+ * to be not reliable at all.
+ * Read by the registers instead.
+ */
+static int sun8i_sid_read_byte_by_reg(const struct sunxi_sid *sid,
+				      const unsigned int offset,
+				      u8 *out)
+{
+	u32 word;
+	int ret;
+
+	ret = sun8i_sid_register_readout(sid, offset & ~0x03, &word);
+
+	if (ret)
+		return ret;
+
+	*out = (word >> ((offset & 0x3) * 8)) & 0xff;
+
+	return 0;
+}
+
+static int sun8i_sid_read_by_reg(void *context, unsigned int offset,
+				 void *val, size_t bytes)
+{
+	struct sunxi_sid *sid = context;
+	u8 *buf = val;
+	int ret;
+
+	while (bytes--) {
+		ret = sun8i_sid_read_byte_by_reg(sid, offset++, buf++);
+		if (ret)
+			return ret;
+	}
+
 	return 0;
 }
 
@@ -131,26 +174,12 @@ static int sunxi_sid_probe(struct platform_device *pdev)
 
 	size = cfg->size;
 
-	if (cfg->need_register_readout) {
-		/*
-		 * H3's SID controller have a bug that the value at 0x200
-		 * offset is not the correct value when the hardware is reseted.
-		 * However, after doing a register-based read operation, the
-		 * value become right.
-		 * Do a full read operation here, but ignore its value
-		 * (as it's more fast to read by direct MMIO value than
-		 * with registers)
-		 */
-		for (i = 0; i < (size >> 2); i++) {
-			ret = sun8i_sid_register_readout(sid, i);
-			if (ret)
-				return ret;
-		}
-	}
-
 	econfig.size = size;
 	econfig.dev = dev;
-	econfig.reg_read = sunxi_sid_read;
+	if (cfg->need_register_readout)
+		econfig.reg_read = sun8i_sid_read_by_reg;
+	else
+		econfig.reg_read = sunxi_sid_read;
 	econfig.priv = sid;
 	nvmem = nvmem_register(&econfig);
 	if (IS_ERR(nvmem))
@@ -163,7 +192,7 @@ static int sunxi_sid_probe(struct platform_device *pdev)
 	}
 
 	for (i = 0; i < size; i++)
-		randomness[i] = sunxi_sid_read_byte(sid, i);
+		econfig.reg_read(sid, i, &randomness[i], 1);
 
 	add_device_randomness(randomness, size);
 	kfree(randomness);