linux-kernel - [PATCH] eeprom: at25: fram: Detect and support inside-out chip variants

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Message-ID: <20250702222927.864875-1-alexander.sverdlin@siemens.com>
Date: Thu,  3 Jul 2025 00:29:26 +0200
From: "A. Sverdlin" <alexander.sverdlin@...mens.com>
To: linux-kernel@...r.kernel.org
Cc: Alexander Sverdlin <alexander.sverdlin@...mens.com>,
	Arnd Bergmann <arnd@...db.de>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: [PATCH] eeprom: at25: fram: Detect and support inside-out chip variants

From: Alexander Sverdlin <alexander.sverdlin@...mens.com>

Infineon seems to be confused with the order ID bytes should be presented
by the FRAM chips and to be on the safe side they offer chips which are
either JEDEC conform or the full opposite of the latter.

Examples of the chips which present ID bytes in the reversed order are:
CY15B102QN
CY15B204QSN

Let's support them nevertheless. Except reversing the ID bytes, they also
have quite different density encoding even across EXCELON(tm) family.

The patch has been tested with the above two chips.

Signed-off-by: Alexander Sverdlin <alexander.sverdlin@...mens.com>
---
 drivers/misc/eeprom/at25.c | 22 +++++++++++++++++++---
 1 file changed, 19 insertions(+), 3 deletions(-)

diff --git a/drivers/misc/eeprom/at25.c b/drivers/misc/eeprom/at25.c
index 20611320e7152..2d0492867054f 100644
--- a/drivers/misc/eeprom/at25.c
+++ b/drivers/misc/eeprom/at25.c
@@ -385,17 +385,33 @@ static int at25_fram_to_chip(struct device *dev, struct spi_eeprom *chip)
 
 	/* Get ID of chip */
 	fm25_aux_read(at25, id, FM25_RDID, FM25_ID_LEN);
+	/* There are inside-out FRAM variations, detect them and reverse the ID bytes */
+	if (id[6] == 0x7f && id[2] == 0xc2)
+		for (i = 0; i < ARRAY_SIZE(id) / 2; i++) {
+			u8 tmp = id[i];
+			int j = ARRAY_SIZE(id) - i - 1;
+
+			id[i] = id[j];
+			id[j] = tmp;
+		}
 	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) {
+
+	switch (id[7]) {
+	case 0x21 ... 0x26:
+		chip->byte_len = BIT(id[7] - 0x21 + 4) * 1024;
+		break;
+	case 0x2a ... 0x30:
+		/* CY15B116QN ... CY15B116QN */
+		chip->byte_len = BIT(((id[7] >> 1) & 0xf) + 13);
+		break;
+	default:
 		dev_err(dev, "Error: unsupported size (id %02x)\n", id[7]);
 		return -ENODEV;
 	}
 
-	chip->byte_len = BIT(id[7] - 0x21 + 4) * 1024;
 	if (chip->byte_len > 64 * 1024)
 		chip->flags |= EE_ADDR3;
 	else
-- 
2.50.0