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

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

diff --git a/drivers/media/video/em28xx/em28xx-cards.c b/drivers/media/video/em28xx/em28xx-cards.c
index fd7a8a5..e88bf67 100644 (file)
--- 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);