[PATCH 2/2] misc: eeprom_93xx46: Add quirk to support Microchip 93LC46B eeprom

[Aswath Govindraju]

A dummy zero bit is sent preceding the data during a read transfer by the
Microchip 93LC46B eeprom (section 2.7 of[1]). This results in right shift
of data during a read. In order to ignore this bit a quirk can be added to
send an extra zero bit after the read address.

Add a quirk to ignore the zero bit sent before data by adding a zero bit
after the read address.

[1] - https://www.mouser.com/datasheet/2/268/20001749K-277859.pdf

Signed-off-by: Aswath Govindraju <a-govindraju@xxxxxx>
---
 drivers/misc/eeprom/eeprom_93xx46.c | 15 +++++++++++++++
 include/linux/eeprom_93xx46.h       |  2 ++
 2 files changed, 17 insertions(+)

diff --git a/drivers/misc/eeprom/eeprom_93xx46.c b/drivers/misc/eeprom/eeprom_93xx46.c
index 7c45f82b4302..b144e7981f36 100644
--- a/drivers/misc/eeprom/eeprom_93xx46.c
+++ b/drivers/misc/eeprom/eeprom_93xx46.c
@@ -35,6 +35,10 @@ static const struct eeprom_93xx46_devtype_data atmel_at93c46d_data = {
 		  EEPROM_93XX46_QUIRK_INSTRUCTION_LENGTH,
 };
 
+static const struct eeprom_93xx46_devtype_data microchip_93LC46B_data = {
+	.quirks = EEPROM_93XX46_QUIRK_EXTRA_READ_CYCLE,
+};
+
 struct eeprom_93xx46_dev {
 	struct spi_device *spi;
 	struct eeprom_93xx46_platform_data *pdata;
@@ -55,6 +59,11 @@ static inline bool has_quirk_instruction_length(struct eeprom_93xx46_dev *edev)
 	return edev->pdata->quirks & EEPROM_93XX46_QUIRK_INSTRUCTION_LENGTH;
 }
 
+static inline bool has_quirk_extra_read_cycle(struct eeprom_93xx46_dev *edev)
+{
+	return edev->pdata->quirks & EEPROM_93XX46_QUIRK_EXTRA_READ_CYCLE;
+}
+
 static int eeprom_93xx46_read(void *priv, unsigned int off,
 			      void *val, size_t count)
 {
@@ -96,6 +105,11 @@ static int eeprom_93xx46_read(void *priv, unsigned int off,
 		dev_dbg(&edev->spi->dev, "read cmd 0x%x, %d Hz\n",
 			cmd_addr, edev->spi->max_speed_hz);
 
+		if (has_quirk_extra_read_cycle(edev)) {
+			cmd_addr <<= 1;
+			bits += 1;
+		}
+
 		spi_message_init(&m);
 
 		t[0].tx_buf = (char *)&cmd_addr;
@@ -363,6 +377,7 @@ static void select_deassert(void *context)
 static const struct of_device_id eeprom_93xx46_of_table[] = {
 	{ .compatible = "eeprom-93xx46", },
 	{ .compatible = "atmel,at93c46d", .data = &atmel_at93c46d_data, },
+	{ .compatible = "microchip,93LC46B", .data = &microchip_93LC46B_data, },
 	{}
 };
 MODULE_DEVICE_TABLE(of, eeprom_93xx46_of_table);
diff --git a/include/linux/eeprom_93xx46.h b/include/linux/eeprom_93xx46.h
index eec7928ff8fe..99580c22f91a 100644
--- a/include/linux/eeprom_93xx46.h
+++ b/include/linux/eeprom_93xx46.h
@@ -16,6 +16,8 @@ struct eeprom_93xx46_platform_data {
 #define EEPROM_93XX46_QUIRK_SINGLE_WORD_READ		(1 << 0)
 /* Instructions such as EWEN are (addrlen + 2) in length. */
 #define EEPROM_93XX46_QUIRK_INSTRUCTION_LENGTH		(1 << 1)
+/* Add extra cycle after address during a read */
+#define EEPROM_93XX46_QUIRK_EXTRA_READ_CYCLE		BIT(2)
 
 	/*
 	 * optional hooks to control additional logic
-- 
2.17.1