Re: [PATCH v3 06/14] Documentation: drm/bridge: add document for analogix_dp

[Yakir Yang]

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@xxxxxxxxxx> 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@xxxxxxxxxxxxxx> 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:
> >
> > *ïïCompliant with DisplayPortTM Specification, Version 1.2.
> > ïïCompliant with eDPTM Specification, Version 1.3.
> > ïïHDCP v1.3 amendment for DisplayPortTM Revision 1.0.
> > ïïMain 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


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