Messages in this thread | | | Date | Fri, 25 Jun 2021 08:55:41 -0700 | From | khsieh@codeauro ... | Subject | Re: [PATCH v2] arm64/dts/qcom/sc7180: Add Display Port dt node |
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On 2021-06-22 19:52, Bjorn Andersson wrote: > On Tue 22 Jun 15:23 CDT 2021, Stephen Boyd wrote: > >> Quoting Bjorn Andersson (2021-06-18 14:41:50) >> > On Fri 18 Jun 15:49 CDT 2021, Stephen Boyd wrote: >> > >> > > Quoting khsieh@codeaurora.org (2021-06-10 09:54:05) >> > > > On 2021-06-08 16:10, Bjorn Andersson wrote: >> > > > > On Tue 08 Jun 17:44 CDT 2021, Stephen Boyd wrote: >> > > > > >> > > > >> Honestly I suspect the DP PHY is _not_ in the CX domain as CX is for >> > > > >> digital logic. Probably the PLL is the hardware that has some minimum >> > > > >> CX >> > > > >> requirement, and that flows down into the various display clks like >> > > > >> the >> > > > >> link clk that actually clock the DP controller hardware. The mdss_gdsc >> > > > >> probably gates CX for the display subsystem (mdss) so if we had proper >> > > > >> corner aggregation logic we could indicate that mdss_gdsc is a child >> > > > >> of >> > > > >> the CX domain and then make requests from the DP driver for particular >> > > > >> link frequencies on the mdss_gdsc and then have that bubble up to CX >> > > > >> appropriately. I don't think any of that sort of code is in place >> > > > >> though, right? >> > > > > >> > > > > I haven't checked sc7180, but I'm guessing that it's following the >> > > > > other >> > > > > modern platforms, where all the MDSS related pieces (including e.g. >> > > > > dispcc) lives in the MMCX domain, which is separate from CX. >> > > > > >> > > > > So the parent of MDSS_GDSC should be MMCX, while Kuogee's answer (and >> > > > > the dp-opp-table) tells us that the PLL lives in the CX domain. >> > > >> > > Isn't MMCX a "child" of CX? At least my understanding is that MMCX is >> > > basically a GDSC that clamps all of multimedia hardware block power >> > > logic so that the leakage is minimized when multimedia isn't in use, >> > > i.e. the device is suspended. In terms of bumping up the voltage we have >> > > to pin that on CX though as far as I know because that's the only power >> > > domain that can actually change voltage, while MMCX merely gates that >> > > voltage for multimedia. >> > > >> > >> > No, MMCX is a separate rail from CX, which powers the display blocks and >> > is parent of MDSS_GDSC. But I see in rpmhpd that sc7180 is not one of >> > these platforms, so I presume this means that the displayport controller >> > thereby sits in MDSS_GDSC parented by CX. >> > >> > But in line with what you're saying, the naming of the supplies to the >> > QMP indicates that the power for the PLLs is static. As such the only >> > moving things would be the clock rates in the DP controller and as such >> > that's what needs to scale the voltage. >> > >> > So if the resources we're scaling is the clocks in the DP controller >> > then the gist of the patch is correct. The only details I see is that >> > the DP controller actually sits in MDSS_GDSC - while it should control >> > the level of its parent (CX). Not sure if we can describe that in a >> > simple way. >> >> Right. I'm not sure things could be described any better right now. If >> we need to change this to be MDSS_GDSC power domain and control the >> level of the parent then I suppose we'll have to make some sort of DT >> change and pair that with a driver change. Maybe if that happens we >> can >> just pick a new compatible and leave the old code in place. >> > > I would prefer that we stay away from making up a new compatible for > that, but let's see when we get there. > >> Are you happy enough with this current patch? >> > > Yes, I think this looks good. > >> > >> > >> > PS. Why does the node name of the opp-table have to be globally unique? >> >> Presumably the opp table node name can be 'opp-table' as long as it >> lives under the node that's using it. If the opp table is at / or /soc >> then it will need to be unique. I'd prefer just 'opp-table' if >> possible. > > I asked the same question (if it has to be globally unique) in the > patch > adding sdhci nodes for sc7280 and I didn't get a sufficient answer... > > So now I do want to know why "opp-table" wouldn't be sufficient name > for > these device-internal nodes. > my opinion is dp_opp_table is more consistency with mdp and dsi. Either one is fine. Please let me know asap. > Regards, > Bjorn
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