<html> <head> <base href="https://bugs.freedesktop.org/" /> </head> <body> <div> <a class="bz_bug_link bz_status_NEW " title="NEW - Apple miniDP-to-VGA adapter doesn't work anymore since Kernel 4.1" href="https://bugs.freedesktop.org/show_bug.cgi?id=91451#c12">Comment # 12</a> on <a class="bz_bug_link bz_status_NEW " title="NEW - Apple miniDP-to-VGA adapter doesn't work anymore since Kernel 4.1" href="https://bugs.freedesktop.org/show_bug.cgi?id=91451">bug 91451</a> from <a class="email" href="mailto:simon@farnz.org.uk" title="Simon Farnsworth <simon@farnz.org.uk>"> Simon Farnsworth</a> <pre>So, a suggestion if anyone's got time to work on this: drm_kms_helper.dp_aux_i2c_transfer_size sets the number of bytes of I2C data we try to transfer in a single DP AUX transaction; the maximum is 16, the minimum is 1 byte. I have devices that need 16 bytes per transaction, otherwise they fail; it looks like the Apple adapter fails if you try to transfer more than 4 bytes per transaction. drm_dp_i2c_xfer currently only reduces the transfer size if the DP device returns a partial success (e.g. 4 bytes of I2C data returned when we asked for 16 will cause us to try with 4 bytes per transaction in future). With a bit of care, it could also learn that when the I2C transaction reaches the retry limit and the only response to DP AUX transactions was DP_AUX_NATIVE_REPLY_DEFER, it's time to reduce the transaction size. Note that you do expect some DP_AUX_NATIVE_REPLY_DEFERs in normal operation - they're how the device tells you that it can't reply yet.</pre> </div> <hr> You are receiving this mail because: <ul> <li>You are the QA Contact for the bug.</li> <li>You are on the CC list for the bug.</li> <li>You are the assignee for the bug.</li> </ul> </body> </html>