[RFC PATCH 1/2] eeprom: at25: support Cypress FRAMs without device ID

[Markus Heidelberg <m.heidelberg@cab.de>]

Not all FRAM chips have a device ID and implement the corresponding read
command. For such chips this led to the following error on module
loading:

    at25 spi2.0: Error: no Cypress FRAM (id 00)

The device ID contains the memory size, so devices without this ID are
supported now by setting the size manually in Devicetree using the
"size" property.

Tested with FM25L16B.

According to Infineon/Cypress datasheets, these FRAMs have a device ID:

    FM25V01A
    FM25V02A
    FM25V05
    FM25V10
    FM25V20A
    FM25VN10

but these do not:

    FM25040B
    FM25640B
    FM25C160B
    FM25CL64B
    FM25L04B
    FM25L16B
    FM25W256

So all "FM25V*" FRAMs and only these have a device ID. The letter after
"FM25" (V/C/L/W) only describes the voltage range, though.

Signed-off-by: Markus Heidelberg <m.heidelberg@cab.de>
---
 drivers/misc/eeprom/at25.c | 42 ++++++++++++++++++++++----------------
 1 file changed, 24 insertions(+), 18 deletions(-)

diff --git a/drivers/misc/eeprom/at25.c b/drivers/misc/eeprom/at25.c
index 595ceb9a7126..16ce36c02ed4 100644
--- a/drivers/misc/eeprom/at25.c
+++ b/drivers/misc/eeprom/at25.c
@@ -382,35 +382,41 @@ static int at25_fram_to_chip(struct device *dev, struct spi_eeprom *chip)
 	struct at25_data *at25 = container_of(chip, struct at25_data, chip);
 	u8 sernum[FM25_SN_LEN];
 	u8 id[FM25_ID_LEN];
+	u32 val;
 	int i;
 
 	strscpy(chip->name, "fm25", sizeof(chip->name));
 
-	/* Get ID of chip */
-	fm25_aux_read(at25, id, FM25_RDID, FM25_ID_LEN);
-	if (id[6] != 0xc2) {
-		dev_err(dev, "Error: no Cypress FRAM (id %02x)\n", id[6]);
-		return -ENODEV;
-	}
-	/* Set size found in ID */
-	if (id[7] < 0x21 || id[7] > 0x26) {
-		dev_err(dev, "Error: unsupported size (id %02x)\n", id[7]);
-		return -ENODEV;
+	if (!device_property_read_u32(dev, "size", &val)) {
+		chip->byte_len = val;
+	} else {
+		/* Get ID of chip */
+		fm25_aux_read(at25, id, FM25_RDID, FM25_ID_LEN);
+		if (id[6] != 0xc2) {
+			dev_err(dev, "Error: no Cypress FRAM (id %02x)\n", id[6]);
+			return -ENODEV;
+		}
+		/* Set size found in ID */
+		if (id[7] < 0x21 || id[7] > 0x26) {
+			dev_err(dev, "Error: unsupported size (id %02x)\n", id[7]);
+			return -ENODEV;
+		}
+
+		chip->byte_len = BIT(id[7] - 0x21 + 4) * 1024;
+
+		if (id[8]) {
+			fm25_aux_read(at25, sernum, FM25_RDSN, FM25_SN_LEN);
+			/* Swap byte order */
+			for (i = 0; i < FM25_SN_LEN; i++)
+				at25->sernum[i] = sernum[FM25_SN_LEN - 1 - i];
+		}
 	}
 
-	chip->byte_len = BIT(id[7] - 0x21 + 4) * 1024;
 	if (chip->byte_len > 64 * 1024)
 		chip->flags |= EE_ADDR3;
 	else
 		chip->flags |= EE_ADDR2;
 
-	if (id[8]) {
-		fm25_aux_read(at25, sernum, FM25_RDSN, FM25_SN_LEN);
-		/* Swap byte order */
-		for (i = 0; i < FM25_SN_LEN; i++)
-			at25->sernum[i] = sernum[FM25_SN_LEN - 1 - i];
-	}
-
 	chip->page_size = PAGE_SIZE;
 	return 0;
 }
-- 
2.43.0