drivers/video/i810/i810-i2c.c: fix i2c bus handling

These patch fix a longstanding bug in the i810 frame buffer driver.

The handling of the i2c bus is wrong: A 1 bit should not written to the
i2c, these will be done by switch the i2c to input. Driving an 1 bit
active is against the i2c spec.

An active driven of a 1 bit will result in very strange error, depending
which side is the more powerful one. In my case it depends on the
temperature of the Display-Controller-EEprom: With an cold eprom a got
the correct EDID datas, with a warm one some of the 1 bits was 0 :-(

The same bug is also in the intelfb driver in the file
drivers/video/intelfb/intelfb_i2c.c. The functions intelfb_gpio_setscl()
and intelfb_gpio_setsda() do drive the 1 bit active to the i2c bus. But
since i have no card which is used by the intelfb driver i cannot fix
it.

Signed-off-by: Stefani Seibold <stefani@seibold.net>
Cc: Paul Mundt <lethal@linux-sh.org>
Cc: Jean Delvare <khali@linux-fr.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>

1 files changed, 8 insertions, 4 deletions

diff --git a/drivers/video/i810/i810-i2c.c b/drivers/video/i810/i810-i2c.c
index cd2c728a809b..7db17d0d8a8c 100644
--- a/drivers/video/i810/i810-i2c.c
+++ b/drivers/video/i810/i810-i2c.c
@@ -45,8 +45,10 @@ static void i810i2c_setscl(void *data, int state)
         struct i810fb_par         *par = chan->par;
         u8                        __iomem *mmio = par->mmio_start_virtual;
 
-        i810_writel(mmio, chan->ddc_base, (state ? SCL_VAL_OUT : 0) | SCL_DIR |
-                    SCL_DIR_MASK | SCL_VAL_MASK);
+        if (state)
+                i810_writel(mmio, chan->ddc_base, SCL_DIR_MASK | SCL_VAL_MASK);
+        else
+                i810_writel(mmio, chan->ddc_base, SCL_DIR | SCL_DIR_MASK | SCL_VAL_MASK);
         i810_readl(mmio, chan->ddc_base);       /* flush posted write */
 }
 
@@ -56,8 +58,10 @@ static void i810i2c_setsda(void *data, int state)
         struct i810fb_par         *par = chan->par;
         u8                        __iomem *mmio = par->mmio_start_virtual;
 
-        i810_writel(mmio, chan->ddc_base, (state ? SDA_VAL_OUT : 0) | SDA_DIR |
-                    SDA_DIR_MASK | SDA_VAL_MASK);
+        if (state)
+                i810_writel(mmio, chan->ddc_base, SDA_DIR_MASK | SDA_VAL_MASK);
+        else
+                i810_writel(mmio, chan->ddc_base, SDA_DIR | SDA_DIR_MASK | SDA_VAL_MASK);
         i810_readl(mmio, chan->ddc_base);       /* flush posted write */
 }