V4L/DVB (6546): Add comments for the hint methods

Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>

1 files changed, 24 insertions, 5 deletions

diff --git a/drivers/media/video/em28xx/em28xx-cards.c b/drivers/media/video/em28xx/em28xx-cards.c
index fd7a8a5fba66..e88bf6700e63 100644
--- a/drivers/media/video/em28xx/em28xx-cards.c
+++ b/drivers/media/video/em28xx/em28xx-cards.c
@@ -397,11 +397,13 @@ struct usb_device_id em28xx_id_table [] = {
 };
 MODULE_DEVICE_TABLE (usb, em28xx_id_table);
 
-static struct em28xx_hash_table em28xx_hash [] = {
+/* EEPROM hash table for devices with generic USB IDs */
+static struct em28xx_hash_table em28xx_eeprom_hash [] = {
         /* P/N: SA 60002070465 Tuner: TVF7533-MF */
         { 0x6ce05a8f, EM2820_BOARD_PROLINK_PLAYTV_USB2, TUNER_YMEC_TVF_5533MF },
 };
 
+/* I2C devicelist hash table for devices with generic USB IDs */
 static struct em28xx_hash_table em28xx_i2c_hash[] = {
         { 0xb06a32c3, EM2800_BOARD_TERRATEC_CINERGY_200, TUNER_LG_PAL_NEW_TAPC },
         { 0xf51200e3, EM2800_BOARD_VGEAR_POCKETTV, TUNER_LG_PAL_NEW_TAPC },
@@ -484,10 +486,18 @@ static int em28xx_hint_board(struct em28xx *dev)
 {
         int i;
 
-        for (i = 0; i < ARRAY_SIZE(em28xx_hash); i++) {
-                if (dev->hash == em28xx_hash[i].hash) {
-                        dev->model = em28xx_hash[i].model;
-                        dev->tuner_type = em28xx_hash[i].tuner;
+        /* HINT method: EEPROM
+         *
+         * This method works only for boards with eeprom.
+         * Uses a hash of all eeprom bytes. The hash should be
+         * unique for a vendor/tuner pair.
+         * There are a high chance that tuners for different
+         * video standards produce different hashes.
+         */
+        for (i = 0; i < ARRAY_SIZE(em28xx_eeprom_hash); i++) {
+                if (dev->hash == em28xx_eeprom_hash[i].hash) {
+                        dev->model = em28xx_eeprom_hash[i].model;
+                        dev->tuner_type = em28xx_eeprom_hash[i].tuner;
 
                         em28xx_errdev("Your board has no unique USB ID.\n");
                         em28xx_errdev("A hint were successfully done, "
@@ -504,6 +514,15 @@ static int em28xx_hint_board(struct em28xx *dev)
                 }
         }
 
+        /* HINT method: I2C attached devices
+         *
+         * This method works for all boards.
+         * Uses a hash of i2c scanned devices.
+         * Devices with the same i2c attached chips will
+         * be considered equal.
+         * This method is less precise than the eeprom one.
+         */
+
         /* user did not request i2c scanning => do it now */
         if (!dev->i2c_hash)
                 em28xx_do_i2c_scan(dev);