On Tue, Apr 16, 2013 at 09:53:24AM +0200, "David Müller (ELSOFT AG)" wrote: > Hello > > I have a 855GME based system with a TFP410 DVO transmitter and running a > vanilla Linux-3.8 kernel. > > With the activation of the hardware assisted GMBUS feature (somewhere > near kernel 3.5), the detection of the TFP410 DVO transmitter has become > flacky, which results in an unusable DVO port. > > As a first test, i reduced the I2C frequency from 100kHz to 50kHz and > the problem vanished. I used a scope to check the signal quality on the > I2C lines to the DVO transmitter, but everything seems to be within the > specs. > > I also checked the whole DVO transmitter initialisation sequence defined > in "intel_dvo.c" and there i noticed that the I2C communication is > completely messed up for 1 or 2 I2C transaction after the receipt of the > first NAK (in my case, this will be for the CH7xxx chip at addr 0x76). > > In the "intel_i2c.c" file, there is a remark that one has to be careful > when clearing the NAK condition, otherwise the next I2C transaction may > fail. I played around with this piece of code by adding additional > delays but to no avail so far. > > In the same file, there is also a line which disables the hardware > assisted GMBUS functionality for i830 based system. > Does anybody know if the 855GME may be struck by the same problem as the > i830? > > > Currenty i have figured out two possible work-arounds: > - add "IS_I85X()" to the list of broken systems > - reduce the clock rate from 100kHz to 50kHz I guess we should force bit-banging like we already do for sdvo outputs, see the calls to intel_gmbus_force_bit in intel_sdvo.c. Can you please write such a patch, test it on your machine (I don't have any gen2 dvo machines) and then submit it for inclusion? Please cc me on the patch (and please also cc the intel-gfx mailing list) so it doesn't get lost. Thanks, Daniel -- Daniel Vetter Software Engineer, Intel Corporation +41 (0) 79 365 57 48 - http://blog.ffwll.ch _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/dri-devel
