<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#c15">Comment # 15</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>(In reply to Ville Syrjala from <a href="show_bug.cgi?id=91451#c13">comment #13</a>) > (In reply to Simon Farnsworth from <a href="show_bug.cgi?id=91451#c12">comment #12</a>) > > 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. > > I don't think we should need to reduce the transfer size. What we should do > is figure out how long the transfer might reasonably take, and adjust our > timeouts accordingly. I have an e-mail report saying that the following patch appears to help; Ville, can you take over on this? diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c index 80a02a4..a17444f 100644 --- a/drivers/gpu/drm/drm_dp_helper.c +++ b/drivers/gpu/drm/drm_dp_helper.c @@ -440,7 +440,7 @@ static int drm_dp_i2c_do_msg(struct drm_dp_aux *aux, struct drm_dp_aux_msg *msg) * is required to retry at least seven times upon receiving AUX_DEFER * before giving up the AUX transaction. */ - for (retry = 0, defer_i2c = 0; retry < (7 + defer_i2c); retry++) { + for (retry = 0, defer_i2c = 0; retry < (70 + defer_i2c); retry++) { mutex_lock(&aux->hw_mutex); ret = aux->transfer(aux, msg); mutex_unlock(&aux->hw_mutex);</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>