fb_ddc: Fix DDC lines quirk
PATCH 1/1 fb_ddc: Fix DDC lines quirk
The code in fb_ddc_read() is said to be based on the implementation of the radeon driver:
http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=fc5891c8a3ba284f13994d7bc1f1bfa8283982de
However, comparing the old radeon driver code with the new fb_ddc code reveals some differences. Most notably, the I2C bus lines are held at the end of the function, while the original code was releasing them (as the comment above correctly says.)
There are a few other differences, which appear to be responsible for read failures on my system. While tracing low-level I2C code in i2c-algo-bit, I noticed that the initial attempt to read the EDID always failed. It takes one retry for the read to succeed. As we are about to remove this automatic retry property from i2c-algo-bit, reading the EDID would really fail.
As a summary, the I2C lines quirk which is supposedly needed to read EDID on some older monitors is currently breaking the (first) read on all other monitors (and might not even work with older ones - did anyone try since October 2006?)
After applying the patch below, which makes the code in fb_ddc_read() really similar to what the radeon driver used to have, the first EDID read succeeds again.
On top of that, as it appears that this code has been broken for one year now and nobody seems to have complained, I'm curious if it makes sense to keep this quirk in place. It makes the code more complex and slower just for the sake of monitors which I guess nobody uses anymore. Can't we just get rid of it?
--- drivers/video/fb_ddc.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-)
drivers/video/fb_ddc.c +4 -4
@@ -56,13 +56,12 @@ unsigned char *fb_ddc_read(struct i2c_adint i, j; algo_data->setscl (algo_data->data,1 ); - algo_data->setscl (algo_data->data,0 );for (i =0 ; i <3 ; i++) {/* For some old monitors we need the * following process to initialize/stop DDC */ - algo_data->setsda (algo_data->data,0 ); + algo_data->setsda (algo_data->data,1 );msleep (13 ); algo_data->setscl (algo_data->data,1 );
@@ -97,14 +96,15 @@ unsigned char *fb_ddc_read(struct i2c_ad algo_data->setsda (algo_data->data,1 );msleep (15 ); algo_data->setscl (algo_data->data,0 ); + algo_data->setsda (algo_data->data,0 );if (edid)break ; }/* Release the DDC lines when done or the Apple Cinema HD display * will switch off */ - algo_data->setsda (algo_data->data,0 ); - algo_data->setscl (algo_data->data,0 ); + algo_data->setsda (algo_data->data,1 ); + algo_data->setscl (algo_data->data,1 );return edid; }
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Jean Delvare ------------------------------------------------------------------------- This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2005. http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/
Quoted 8 lines · Jean Delvare
On top of that, as it appears that this code has been broken for one year now and nobody seems to have complained, I'm curious if it makes sense to keep this quirk in place. It makes the code more complex and slower just for the sake of monitors which I guess nobody uses anymore. Can't we just get rid of it?
Signed-off-by Jean Delvare <[email protected]>
I'll have to double check, I suspect some Apple monitors may choke on the "proper" way of releasing the lines (shut down assuming no more host is connected, some stupid trick they do). I'll test when I get a chance.
Regarding the quirk, well... I think the X folks are tempted to get rid of it too.
Ben.
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Quoted 8 lines · Jean Delvare
The code in
fb_ddc_read()is said to be based on the implementation of the radeon driver:
http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=fc5891c8a3ba284f13994d7bc1f1bfa8283982deHowever, comparing the old radeon driver code with the new
fb_ddccode reveals some differences. Most notably, the I2C bus lines are held at the end of the function, while the original code was releasing them (as the comment above correctly says.)
.../...
Quoted 1 line
Signed-off-by Jean Delvare <[email protected]>
Quoted 31 lines
--- drivers/video/fb_ddc.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-)drivers/video/fb_ddc.c +2
-2@@ -56,13 +56,12 @@ unsigned char *fb_ddc_read(struct i2c_adint i, j; algo_data->setscl (algo_data->data,1 ); - algo_data->setscl (algo_data->data,0 );for (i =0 ; i <3 ; i++) {/* For some old monitors we need the * following process to initialize/stop DDC */ - algo_data->setsda (algo_data->data,0 ); + algo_data->setsda (algo_data->data,1 );msleep (13 ); algo_data->setscl (algo_data->data,1 );@@ -97,14 +96,15 @@ unsigned char *fb_ddc_read(struct i2c_ad algo_data->setsda (algo_data->data,1 );msleep (15 ); algo_data->setscl (algo_data->data,0 ); + algo_data->setsda (algo_data->data,0 );if (edid)break ; }
drivers/video/fb_ddc.c unsigned char *fb_ddc_read(struct i2c_ad · line 110
Quoted 10 lines
drivers/video/fb_ddc.c +2
-2/* Release the DDC lines when done or the Apple Cinema HD display * will switch off */ - algo_data->setsda (algo_data->data,0 ); - algo_data->setscl (algo_data->data,0 ); + algo_data->setsda (algo_data->data,1 ); + algo_data->setscl (algo_data->data,1 );return edid; }
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Quoted 11 lines · Benjamin Herrenschmidt
Quoted 8 lines · Jean Delvare
The code in
fb_ddc_read()is said to be based on the implementation of the radeon driver:
http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=fc5891c8a3ba284f13994d7bc1f1bfa8283982deHowever, comparing the old radeon driver code with the new
fb_ddccode reveals some differences. Most notably, the I2C bus lines are held at the end of the function, while the original code was releasing them (as the comment above correctly says.)
Quoted 5 lines
.../...
Quoted 1 line
Signed-off-by Jean Delvare <[email protected]>
Thanks. Antonino, this patch fixes two reported regressions. Can you please send it to Linus before 2.6.24 is released? Thanks.
Quoted 42 lines
Quoted 42 lines
--- drivers/video/fb_ddc.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-)drivers/video/fb_ddc.c +4
-4@@ -56,13 +56,12 @@ unsigned char *fb_ddc_read(struct i2c_adint i, j; algo_data->setscl (algo_data->data,1 ); - algo_data->setscl (algo_data->data,0 );for (i =0 ; i <3 ; i++) {/* For some old monitors we need the * following process to initialize/stop DDC */ - algo_data->setsda (algo_data->data,0 ); + algo_data->setsda (algo_data->data,1 );msleep (13 ); algo_data->setscl (algo_data->data,1 );@@ -97,14 +96,15 @@ unsigned char *fb_ddc_read(struct i2c_ad algo_data->setsda (algo_data->data,1 );msleep (15 ); algo_data->setscl (algo_data->data,0 ); + algo_data->setsda (algo_data->data,0 );if (edid)break ; }/* Release the DDC lines when done or the Apple Cinema HD display * will switch off */ - algo_data->setsda (algo_data->data,0 ); - algo_data->setscl (algo_data->data,0 ); + algo_data->setsda (algo_data->data,1 ); + algo_data->setscl (algo_data->data,1 );return edid; }
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Jean Delvare ------------------------------------------------------------------------- This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2005. http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/
Quoted 12 lines · Jean Delvare
Quoted 11 lines · Benjamin Herrenschmidt
Quoted 8 lines · Jean Delvare
The code in
fb_ddc_read()is said to be based on the implementation of the radeon driver:
http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=fc5891c8a3ba284f13994d7bc1f1bfa8283982deHowever, comparing the old radeon driver code with the new
fb_ddccode reveals some differences. Most notably, the I2C bus lines are held at the end of the function, while the original code was releasing them (as the comment above correctly says.)
Quoted 8 lines
Quoted 5 lines
.../...
Quoted 1 line
Signed-off-by Jean Delvare <[email protected]>Thanks. Antonino, this patch fixes two reported regressions. Can you please send it to Linus before 2.6.24 is released? Thanks.
It should also be send to -stable I believe and possibly distros.
Cheers,
Ben.
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