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, 6 insertions, 0 deletions

diff --git a/Documentation/video4linux/bttv/Insmod-options b/Documentation/video4linux/bttv/Insmod-options
index fc94ff235ff..bb7c2cac791 100644
--- a/Documentation/video4linux/bttv/Insmod-options
+++ b/Documentation/video4linux/bttv/Insmod-options
@@ -54,6 +54,12 @@ bttv.o
                                 dropouts.
                 chroma_agc=0/1  AGC of chroma signal, off by default.
                 adc_crush=0/1   Luminance ADC crush, on by default.
+                i2c_udelay=     Allow reduce I2C speed. Default is 5 usecs
+                                (meaning 66,67 Kbps). The default is the
+                                maximum supported speed by kernel bitbang
+                                algoritm. You may use lower numbers, if I2C
+                                messages are lost (16 is known to work on
+                                all supported cards).
 
                 bttv_gpio=0/1
                 gpiomask=