[RFC PATCH 1/2] cpufreq: sun50i: Add support for D1's speed bin decoding

[Brandon Cheo Fusi]

Adds support for decoding the efuse value read from D1 efuse speed
bins, and factors out equivalent code for sun50i.

The algorithm is gotten from

https://github.com/Tina-Linux/linux-5.4/blob/master/drivers/cpufreq/sun50i-cpufreq-nvmem.c#L293-L338

and maps an efuse value to either 0 or 1, with 1 meaning stable at
a lower supply voltage for the same clock frequency.

Signed-off-by: Brandon Cheo Fusi <fusibrandon13 at gmail.com>
---
 drivers/cpufreq/sun50i-cpufreq-nvmem.c | 85 +++++++++++++++++++++-----
 1 file changed, 70 insertions(+), 15 deletions(-)

diff --git a/drivers/cpufreq/sun50i-cpufreq-nvmem.c b/drivers/cpufreq/sun50i-cpufreq-nvmem.c
index ccf83780f..28afbe558 100644
--- a/drivers/cpufreq/sun50i-cpufreq-nvmem.c
+++ b/drivers/cpufreq/sun50i-cpufreq-nvmem.c
@@ -25,6 +25,66 @@
 
 static struct platform_device *cpufreq_dt_pdev, *sun50i_cpufreq_pdev;
 
+struct sunxi_cpufreq_data {
+	u32 (*efuse_xlate)(u32 efuse_value);
+};
+
+static u32 sun20i_efuse_xlate(u32 efuse_value)
+{
+	u32 ret;
+
+	switch (efuse_value) {
+	case 0x5e00:
+		/* QFN package */
+		ret = 0;
+		break;
+	case 0x5c00:
+	case 0x7400:
+		/* QFN package */
+		ret = 1;
+		break;
+	case 0x5000:
+	default:
+		/* BGA package */
+		ret = 0;
+	}
+
+	return ret;
+}
+
+static u32 sun50i_efuse_xlate(u32 efuse_value)
+{
+	efuse_value = (efuse_value >> NVMEM_SHIFT) & NVMEM_MASK;
+
+	/*
+	* We treat unexpected efuse values as if the SoC was from
+	* the slowest bin. Expected efuse values are 1-3, slowest
+	* to fastest.
+	*/
+	if (efuse_value >= 1 && efuse_value <= 3)
+		return efuse_value - 1;
+	else
+		return 0;
+}
+
+struct sunxi_cpufreq_data sun20i_cpufreq_data = {
+	.efuse_xlate = sun20i_efuse_xlate,
+};
+
+struct sunxi_cpufreq_data sun50i_cpufreq_data = {
+	.efuse_xlate = sun50i_efuse_xlate,
+};
+
+static const struct of_device_id cpu_opp_match_list[] = {
+	{ .compatible = "allwinner,sun50i-h6-operating-points",
+	  .data = &sun50i_cpufreq_data,
+	},
+	{ .compatible = "allwinner,sun20i-d1-operating-points",
+	  .data = &sun20i_cpufreq_data,
+	},
+	{}
+};
+
 /**
  * sun50i_cpufreq_get_efuse() - Determine speed grade from efuse value
  * @versions: Set to the value parsed from efuse
@@ -36,9 +96,11 @@ static int sun50i_cpufreq_get_efuse(u32 *versions)
 	struct nvmem_cell *speedbin_nvmem;
 	struct device_node *np;
 	struct device *cpu_dev;
-	u32 *speedbin, efuse_value;
+	const struct of_device_id *opp_match;
+	const struct sunxi_cpufreq_data *opp_data;
+	u32 *speedbin, efuse_value = 0;
 	size_t len;
-	int ret;
+	int i;
 
 	cpu_dev = get_cpu_device(0);
 	if (!cpu_dev)
@@ -48,9 +110,8 @@ static int sun50i_cpufreq_get_efuse(u32 *versions)
 	if (!np)
 		return -ENOENT;
 
-	ret = of_device_is_compatible(np,
-				      "allwinner,sun50i-h6-operating-points");
-	if (!ret) {
+	opp_match = of_match_node(cpu_opp_match_list, np);
+	if (!opp_match) {
 		of_node_put(np);
 		return -ENOENT;
 	}
@@ -66,17 +127,11 @@ static int sun50i_cpufreq_get_efuse(u32 *versions)
 	if (IS_ERR(speedbin))
 		return PTR_ERR(speedbin);
 
-	efuse_value = (*speedbin >> NVMEM_SHIFT) & NVMEM_MASK;
+	for (i = 0; i < len; i++)
+		efuse_value |= ((u32)speedbin[i] << (i * 8));
 
-	/*
-	 * We treat unexpected efuse values as if the SoC was from
-	 * the slowest bin. Expected efuse values are 1-3, slowest
-	 * to fastest.
-	 */
-	if (efuse_value >= 1 && efuse_value <= 3)
-		*versions = efuse_value - 1;
-	else
-		*versions = 0;
+	opp_data = opp_match->data;
+	*versions = opp_data->efuse_xlate(efuse_value);
 
 	kfree(speedbin);
 	return 0;
-- 
2.30.2