V4L/DVB (4609): Improved i2c performance on software bitbang algoritm

Software I2C were using a very conservative value of udelay=16, meaning about
20Kbps. According with Philips I2C datasheet, the i2c should answer well for
times at the order of 4.7 us. So, using udelay=5 should work for all devices.
After this patch, the speed should be close to 66,67 Kbps, with the current
kernel software bitbang, with 30/60 duty cycle.
Anyway, added a new parameter (i2c_udelay) that would allow using conservative
values, if eventually a hardware doesn't support the datasheet values.
Thanks to Jean Delvare <khali@linux-fr.org> for pointing this improvement.

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

1 files changed, 16 insertions, 0 deletions

diff --git a/drivers/media/video/bt8xx/bttv-i2c.c b/drivers/media/video/bt8xx/bttv-i2c.c
index 4b562b386fcf..03ee170181f2 100644
--- a/drivers/media/video/bt8xx/bttv-i2c.c
+++ b/drivers/media/video/bt8xx/bttv-i2c.c
@@ -8,6 +8,9 @@
                            & Marcus Metzler (mocm@thp.uni-koeln.de)
     (c) 1999-2003 Gerd Knorr <kraxel@bytesex.org>
 
+    (c) 2005 Mauro Carvalho Chehab <mchehab@infradead.org>
+        - Multituner support and i2c address binding
+
     This program is free software; you can redistribute it and/or modify
     it under the terms of the GNU General Public License as published by
     the Free Software Foundation; either version 2 of the License, or
@@ -45,10 +48,18 @@ static int i2c_debug;
 static int i2c_hw;
 static int i2c_scan;
 module_param(i2c_debug, int, 0644);
+MODULE_PARM_DESC(i2c_hw,"configure i2c debug level");
 module_param(i2c_hw,    int, 0444);
+MODULE_PARM_DESC(i2c_hw,"force use of hardware i2c support, "
+                        "instead of software bitbang");
 module_param(i2c_scan,  int, 0444);
 MODULE_PARM_DESC(i2c_scan,"scan i2c bus at insmod time");
 
+static unsigned int i2c_udelay = 5;
+module_param(i2c_udelay, int, 0444);
+MODULE_PARM_DESC(i2c_udelay,"soft i2c delay at insmod time, in usecs "
+                "(should be 5 or higher). Lower value means higher bus speed.");
+
 /* ----------------------------------------------------------------------- */
 /* I2C functions - bitbanging adapter (software i2c)                       */
 
@@ -426,6 +437,11 @@ int __devinit init_bttv_i2c(struct bttv *btv)
                        sizeof(bttv_i2c_adap_hw_template));
         } else {
                 /* bt848 */
+        /* Prevents usage of invalid delay values */
+                if (i2c_udelay<5)
+                        i2c_udelay=5;
+                bttv_i2c_algo_bit_template.udelay=i2c_udelay;
+
                 memcpy(&btv->c.i2c_adap, &bttv_i2c_adap_sw_template,
                        sizeof(bttv_i2c_adap_sw_template));
                 memcpy(&btv->i2c_algo, &bttv_i2c_algo_bit_template,