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, 10 insertions, 0 deletions

diff --git a/drivers/media/video/cx88/cx88-i2c.c b/drivers/media/video/cx88/cx88-i2c.c
index 2aec4c18268a..a74ed632dda0 100644
--- a/drivers/media/video/cx88/cx88-i2c.c
+++ b/drivers/media/video/cx88/cx88-i2c.c
@@ -43,6 +43,11 @@ static unsigned int i2c_scan = 0;
 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, 0644);
+MODULE_PARM_DESC(i2c_udelay,"i2c delay at insmod time, in usecs "
+                "(should be 5 or higher). Lower value means higher bus speed.");
+
 #define dprintk(level,fmt, arg...)      if (i2c_debug >= level) \
         printk(KERN_DEBUG "%s: " fmt, core->name , ## arg)
 
@@ -202,6 +207,11 @@ static void do_i2c_scan(char *name, struct i2c_client *c)
 /* init + register i2c algo-bit adapter */
 int cx88_i2c_init(struct cx88_core *core, struct pci_dev *pci)
 {
+        /* Prevents usage of invalid delay values */
+        if (i2c_udelay<5)
+                i2c_udelay=5;
+        cx8800_i2c_algo_template.udelay=i2c_udelay;
+
         memcpy(&core->i2c_adap, &cx8800_i2c_adap_template,
                sizeof(core->i2c_adap));
         memcpy(&core->i2c_algo, &cx8800_i2c_algo_template,