misc: eeprom_93xx46: Add quirk to support Microchip 93LC46B eeprom

[ Upstream commit f6f1f8e6e3eea25f539105d48166e91f0ab46dd1 ]

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@ti.com>
Link: https://lore.kernel.org/r/20210105105817.17644-3-a-govindraju@ti.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/drivers/misc/eeprom/eeprom_93xx46.c b/drivers/misc/eeprom/eeprom_93xx46.c
index a3248ebd28c62064883e5b89c443ef42495b2703..182feab6da25b8f8247a3d772968b0a6e8f7431c 100644 (file)
--- a/drivers/misc/eeprom/eeprom_93xx46.c
+++ b/drivers/misc/eeprom/eeprom_93xx46.c
@@ -38,6 +38,10 @@ 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;
@@ -58,6 +62,11 @@ 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)
 {
@@ -99,6 +108,11 @@ 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;
@@ -366,6 +380,7 @@ 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 eec7928ff8fe043a9d10e790a184a908aa14cb4e..99580c22f91a4d1d4ee58e17568b8e44c07cdd17 100644 (file)
--- 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