[PATCH 2/2] mtd: spi-nor: micron-st: Add support for output-driver-strength

[Alexander Stein]

From: Alexander Stein <alexander.stein@xxxxxxxxxxxxxxx>

Micron flashes support this by the Bits [2:0] in the Enhanced Volatile
Configuration Register.
Checked datasheets:
- n25q_128mb_3v_65nm.pdf
- mt25t-qljs-L512-xBA-xxT.pdf

Signed-off-by: Alexander Stein <alexander.stein@xxxxxxxxxxxxxxx>
---
 drivers/mtd/spi-nor/micron-st.c | 109 ++++++++++++++++++++++++++++++++
 1 file changed, 109 insertions(+)

diff --git a/drivers/mtd/spi-nor/micron-st.c b/drivers/mtd/spi-nor/micron-st.c
index c224e59820a1..5d5e7fbc24a2 100644
--- a/drivers/mtd/spi-nor/micron-st.c
+++ b/drivers/mtd/spi-nor/micron-st.c
@@ -16,6 +16,11 @@
 #define SPINOR_MT_OCT_DTR	0xe7	/* Enable Octal DTR. */
 #define SPINOR_MT_EXSPI		0xff	/* Enable Extended SPI (default) */
 
+struct micron_drive_strength {
+	u32 ohms;
+	u8 val;
+};
+
 static int spi_nor_micron_octal_dtr_enable(struct spi_nor *nor, bool enable)
 {
 	struct spi_mem_op op;
@@ -255,8 +260,112 @@ static void micron_st_default_init(struct spi_nor *nor)
 	nor->params->set_4byte_addr_mode = st_micron_set_4byte_addr_mode;
 }
 
+
+/*
+ * Read Micron enhanced volatile configuration register
+ * Return negative if error occurred or configuration register value
+ */
+static int micron_read_evcr(struct spi_nor *nor)
+{
+	int ret;
+
+	if (nor->spimem) {
+		struct spi_mem_op op =
+			SPI_MEM_OP(SPI_MEM_OP_CMD(SPINOR_OP_RD_EVCR, 1),
+				   SPI_MEM_OP_NO_ADDR,
+				   SPI_MEM_OP_NO_DUMMY,
+				   SPI_MEM_OP_DATA_IN(1, nor->bouncebuf, 1));
+
+		ret = spi_mem_exec_op(nor->spimem, &op);
+	} else {
+		ret = nor->controller_ops->read_reg(nor, SPINOR_OP_RD_EVCR, nor->bouncebuf, 1);
+	}
+
+	if (ret < 0) {
+		dev_err(nor->dev, "error %d reading EVCR\n", ret);
+		return ret;
+	}
+
+	return nor->bouncebuf[0];
+}
+
+/*
+ * Write Micron enhanced volatile configuration register
+ * Return negative if error occurred or configuration register value
+ */
+static int micron_write_evcr(struct spi_nor *nor, u8 evcr)
+{
+	nor->bouncebuf[0] = evcr;
+
+	spi_nor_write_enable(nor);
+
+	if (nor->spimem) {
+		struct spi_mem_op op =
+			SPI_MEM_OP(SPI_MEM_OP_CMD(SPINOR_OP_WD_EVCR, 1),
+				   SPI_MEM_OP_NO_ADDR,
+				   SPI_MEM_OP_NO_DUMMY,
+				   SPI_MEM_OP_DATA_OUT(1, nor->bouncebuf, 1));
+
+		return spi_mem_exec_op(nor->spimem, &op);
+	}
+
+	return nor->controller_ops->write_reg(nor, SPINOR_OP_WD_EVCR, nor->bouncebuf, 1);
+}
+
+/*
+ * Supported values from Enahanced Volatile COnfiguration Register (Bits 2:0)
+ */
+static const struct micron_drive_strength drive_strength_data[] = {
+	{ .ohms = 90, .val = 1 },
+	{ .ohms = 45, .val = 3 },
+	{ .ohms = 20, .val = 5 },
+	{ .ohms = 30, .val = 7 },
+};
+
+static struct micron_drive_strength const *micron_st_find_drive_strength_entry(u32 ohms)
+{
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(drive_strength_data); i++) {
+		if (ohms == drive_strength_data[i].ohms)
+			return &drive_strength_data[i];
+	}
+	return NULL;
+}
+
+static void micron_st_post_sfdp(struct spi_nor *nor)
+{
+	struct device_node *np = spi_nor_get_flash_node(nor);
+	u32 ohms;
+
+	if (!np)
+		return;
+
+	if (!of_property_read_u32(np, "output-driver-strength", &ohms)) {
+		struct micron_drive_strength const *entry =
+			micron_st_find_drive_strength_entry(ohms);
+
+		if (entry) {
+			int evcrr = micron_read_evcr(nor);
+
+			if (evcrr >= 0) {
+				u8 evcr = (u8)(evcrr & 0xf8) | entry->val;
+
+				micron_write_evcr(nor, evcr);
+				dev_dbg(nor->dev, "%s: EVCR 0x%x\n", __func__,
+					(u32)micron_read_evcr(nor));
+			}
+		} else {
+			dev_warn(nor->dev,
+				"Invalid output-driver-strength property specified: %u",
+				ohms);
+		}
+	}
+}
+
 static const struct spi_nor_fixups micron_st_fixups = {
 	.default_init = micron_st_default_init,
+	.post_sfdp = micron_st_post_sfdp,
 };
 
 const struct spi_nor_manufacturer spi_nor_micron = {
-- 
2.25.1