Commit:     b64d70825abbf706bbe80be1b11b09514b71f45e
Parent:     e482179d547ff250cab487859b6fc91995bbdbb5
Author:     Jean Delvare <[EMAIL PROTECTED]>
AuthorDate: Wed Nov 28 16:21:35 2007 -0800
Committer:  Linus Torvalds <[EMAIL PROTECTED]>
CommitDate: Thu Nov 29 09:24:52 2007 -0800

    fb_ddc: fix DDC lines quirk
    The code in fb_ddc_read() is said to be based on the implementation of the
    radeon driver:;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
    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?
    Signed-off-by: Jean Delvare <[EMAIL PROTECTED]>
    Acked-by: Benjamin Herrenschmidt <[EMAIL PROTECTED]>
    Tested-by: Roger Leigh <[EMAIL PROTECTED]>
    Tested-by: Michael Buesch <[EMAIL PROTECTED]>
    Cc: "Antonino A. Daplas" <[EMAIL PROTECTED]>
    Signed-off-by: Andrew Morton <[EMAIL PROTECTED]>
    Signed-off-by: Linus Torvalds <[EMAIL PROTECTED]>
 drivers/video/fb_ddc.c |    8 ++++----
 1 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/video/fb_ddc.c b/drivers/video/fb_ddc.c
index f836137..a0df632 100644
--- a/drivers/video/fb_ddc.c
+++ b/drivers/video/fb_ddc.c
@@ -56,13 +56,12 @@ unsigned char *fb_ddc_read(struct i2c_adapter *adapter)
        int 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);
                algo_data->setscl(algo_data->data, 1);
@@ -97,14 +96,15 @@ unsigned char *fb_ddc_read(struct i2c_adapter *adapter)
                algo_data->setsda(algo_data->data, 1);
                algo_data->setscl(algo_data->data, 0);
+               algo_data->setsda(algo_data->data, 0);
                if (edid)
        /* 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;
To unsubscribe from this list: send the line "unsubscribe git-commits-head" in
the body of a message to [EMAIL PROTECTED]
More majordomo info at

Reply via email to