Hi Thierry, å¨ 2015/8/25 22:16, Thierry Reding åé: > On Tue, Aug 25, 2015 at 09:48:01PM +0800, Yakir Yang wrote: >> Hi Thierry & Rob, >> >> å¨ 2015/8/25 21:27, Rob Herring åé: >>> On Tue, Aug 25, 2015 at 4:15 AM, Thierry Reding <treding at nvidia.com> >>> wrote: >>>> On Sun, Aug 23, 2015 at 06:23:14PM -0500, Rob Herring wrote: >>>>> On Wed, Aug 19, 2015 at 9:50 AM, Yakir Yang <ykk at rock-chips.com> wrote: >>>> [...] >>>>>> + -analogix,link-rate: >>>>>> + max link rate supported by the eDP controller. >>>>>> + LINK_RATE_1_62GBPS = 0x6, LINK_RATE_2_70GBPS = >>>>>> 0x0A, >>>>>> + LINK_RATE_5_40GBPS = 0x14 >>>>> Same here. I'd rather see something like "link-rate-mbps" and use the >>>>> actual rate. >>>> There is no need whatsoever to hard-code this in DT. (e)DP provides the >>>> means to detect what rate the link supports and the specification >>>> provides guidance on how to select an appropriate one. >>> Good, even better. >> I do think we still need keep this DT prop yet. >> >> I think drm_dp_help.c could get the "panel" max link-rate and lane-count, >> but it's not enough, we still need knew the "eDP controller" max link-rate >> and lane-count. >> >> Let me show the exact example that happened in my side. When I connect >> my board to my 2K DP-1.2 TV. Analogix dp driver would get the max link-rate >> from dpcd, and the max link-rate is 5.4Gbps. So if I just set eDP controller >> link-rate >> to 5.4Gbps, the DP TV just broken, do not light up normally. >> >> This reason why TV broken is the max link-rate which support by RK3288 eDP >> controller is 2.7Gbps. Here are the exact words that RK3288 eDP TRM said: >> >> *ï¬ï Compliant with DisplayPortTM Specification, Version 1.2. >> ï¬ï Compliant with eDPTM Specification, Version 1.3. >> ï¬ï HDCP v1.3 amendment for DisplayPortTM Revision 1.0. >> ï¬ï Main link containing 4 physical lanes of 2.7/1.62 Gbps/lane >> * >> ** >> >> >> Beside I haven't found there are some registers would indicate the eDP >> controller >> max link-rate and lane-count, so this is why I still instance that we need >> this DT >> prop to indicata "Max rate controller support". >> >> So, I wish you could agree with me on this point. > Your driver should know what link rates it supports and restrict itself > to use those. This is implied by the compatible string and doesn't need > to be duplicated into device tree.
Oh, yeah, good idea :-D Thanks for your point out. - Yakir > Thierry
