# \[PATCH\] fix i810 i2c bug - List: linux-fbdev - 2 messages, 2 authors - Page: https://ratatoskr.run/linux-fbdev/2011/01/3660872/t ## \[PATCH\] fix i810 i2c bug - From: Stefani Seibold \ - Date: 2011-01-03 09:28:03 - Message: https://ratatoskr.run/linux-fbdev/2011/01/3660872.md ```text 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. The patch is against linux next-20101231 - Stefani Signed-off-by: Stefani Seibold --- i810-i2c.c | 12 ++++++++---- 1 file changed, 8 insertions(+), 4 deletions(-) diff -u -N -r -p linux-2.6.35.orig/drivers/video/i810/i810-i2c.c linux-2.6.35/drivers/video/i810/i810-i2c.c --- linux-2.6.35.orig/drivers/video/i810/i810-i2c.c 2010-08-02 00:11:14.000000000 +0200 +++ linux-2.6.35/drivers/video/i810/i810-i2c.c 2010-10-04 12:24:29.000000000 +0200 @@ -45,8 +45,10 @@ static void i810i2c_setscl(void *data, i 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, i 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 */ } ``` ## Re: \[PATCH\] fix i810 i2c bug - From: Paul Mundt \ - Date: 2011-01-06 06:55:28 - Message: https://ratatoskr.run/linux-fbdev/2011/01/3662357.md ```text On Mon, Jan 03, 2011 at 10:28:59AM +0100, Stefani Seibold wrote: > 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. > > The patch is against linux next-20101231 > > - Stefani > > Signed-off-by: Stefani Seibold Applied, thanks. Also adding intelfb people to the Cc so they're aware of the problem, and can follow suit. ```