ath9k: fetch calibration data via nvmem subsystem

On most embedded ath9k devices (like range extenders,
routers, accesspoints, ...) the calibration data is
stored in a MTD partitions named "ART", or "caldata"/
"calibration".

Since commit 4b361cfa86 ("mtd: core: add OTP nvmem provider support"):
All MTD partitions are all automatically available through
the nvmem subsystem.

This feature - together with an nvmem cell definition either
in the platform data or via device-tree allows drivers to get
the data necessary for initializing the WIFI, without having
to wait around for the filesystem and userspace to do
the extractions.

Signed-off-by: Christian Lamparter <chunkeey@gmail.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/f9b732b50a3453fadf3923cc75d365bae3505fe7.1630157099.git.chunkeey@gmail.com

drivers/net/wireless/ath/ath9k/eeprom.c

@@ -135,13 +135,23 @@ static bool ath9k_hw_nvram_read_firmware(const struct firmware *eeprom_blob,
 					 offset, data);
 }
 
+static bool ath9k_hw_nvram_read_nvmem(struct ath_hw *ah, off_t offset,
+				      u16 *data)
+{
+	return ath9k_hw_nvram_read_array(ah->nvmem_blob,
+					 ah->nvmem_blob_len / sizeof(u16),
+					 offset, data);
+}
+
 bool ath9k_hw_nvram_read(struct ath_hw *ah, u32 off, u16 *data)
 {
 	struct ath_common *common = ath9k_hw_common(ah);
 	struct ath9k_platform_data *pdata = ah->dev->platform_data;
 	bool ret;
 
-	if (ah->eeprom_blob)
+	if (ah->nvmem_blob)
+		ret = ath9k_hw_nvram_read_nvmem(ah, off, data);
+	else if (ah->eeprom_blob)
 		ret = ath9k_hw_nvram_read_firmware(ah->eeprom_blob, off, data);
 	else if (pdata && !pdata->use_eeprom)
 		ret = ath9k_hw_nvram_read_pdata(pdata, off, data);

drivers/net/wireless/ath/ath9k/hw.h

@@ -977,6 +977,8 @@ struct ath_hw {
 	bool disable_5ghz;
 
 	const struct firmware *eeprom_blob;
+	u16 *nvmem_blob;	/* devres managed */
+	size_t nvmem_blob_len;
 
 	struct ath_dynack dynack;
 

drivers/net/wireless/ath/ath9k/init.c

@@ -22,6 +22,7 @@
 #include <linux/module.h>
 #include <linux/of.h>
 #include <linux/of_net.h>
+#include <linux/nvmem-consumer.h>
 #include <linux/relay.h>
 #include <linux/dmi.h>
 #include <net/ieee80211_radiotap.h>
@@ -568,6 +569,57 @@ static void ath9k_eeprom_release(struct ath_softc *sc)
 	release_firmware(sc->sc_ah->eeprom_blob);
 }
 
+static int ath9k_nvmem_request_eeprom(struct ath_softc *sc)
+{
+	struct ath_hw *ah = sc->sc_ah;
+	struct nvmem_cell *cell;
+	void *buf;
+	size_t len;
+	int err;
+
+	cell = devm_nvmem_cell_get(sc->dev, "calibration");
+	if (IS_ERR(cell)) {
+		err = PTR_ERR(cell);
+
+		/* nvmem cell might not be defined, or the nvmem
+		 * subsystem isn't included. In this case, follow
+		 * the established "just return 0;" convention of
+		 * ath9k_init_platform to say:
+		 * "All good. Nothing to see here. Please go on."
+		 */
+		if (err == -ENOENT || err == -EOPNOTSUPP)
+			return 0;
+
+		return err;
+	}
+
+	buf = nvmem_cell_read(cell, &len);
+	if (IS_ERR(buf))
+		return PTR_ERR(buf);
+
+	/* run basic sanity checks on the returned nvram cell length.
+	 * That length has to be a multiple of a "u16" (i.e.: & 1).
+	 * Furthermore, it has to be more than "let's say" 512 bytes
+	 * but less than the maximum of AR9300_EEPROM_SIZE (16kb).
+	 */
+	if ((len & 1) == 1 || len < 512 || len >= AR9300_EEPROM_SIZE) {
+		kfree(buf);
+		return -EINVAL;
+	}
+
+	/* devres manages the calibration values release on shutdown */
+	ah->nvmem_blob = (u16 *)devm_kmemdup(sc->dev, buf, len, GFP_KERNEL);
+	kfree(buf);
+	if (IS_ERR(ah->nvmem_blob))
+		return PTR_ERR(ah->nvmem_blob);
+
+	ah->nvmem_blob_len = len;
+	ah->ah_flags &= ~AH_USE_EEPROM;
+	ah->ah_flags |= AH_NO_EEP_SWAP;
+
+	return 0;
+}
+
 static int ath9k_init_platform(struct ath_softc *sc)
 {
 	struct ath9k_platform_data *pdata = sc->dev->platform_data;
@@ -704,6 +756,10 @@ static int ath9k_init_softc(u16 devid, struct ath_softc *sc,
 	if (ret)
 		return ret;
 
+	ret = ath9k_nvmem_request_eeprom(sc);
+	if (ret)
+		return ret;
+
 	if (ath9k_led_active_high != -1)
 		ah->config.led_active_high = ath9k_led_active_high == 1;