linux-kernel - Re: [PATCH v1 2/2] clk: qcom : dispcc: Add support for display port clocks

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Message-ID: <154152409835.88331.14046185859724133804@swboyd.mtv.corp.google.com>
Date:   Tue, 06 Nov 2018 09:08:18 -0800
From:   Stephen Boyd <sboyd@...nel.org>
To:     Michael Turquette <mturquette@...libre.com>,
        Taniya Das <tdas@...eaurora.org>, chandanu@...eaurora.org
Cc:     Andy Gross <andy.gross@...aro.org>,
        David Brown <david.brown@...aro.org>,
        Rajendra Nayak <rnayak@...eaurora.org>,
        linux-arm-msm@...r.kernel.org, linux-soc@...r.kernel.org,
        linux-clk@...r.kernel.org, linux-kernel@...r.kernel.org,
        chandanu@...eaurora.org, linux-arm-msm-owner@...r.kernel.org
Subject: Re: [PATCH v1 2/2] clk: qcom : dispcc: Add support for display port clocks

Quoting Taniya Das (2018-10-31 22:02:22)
> + Chandan from Display Port team,
> 
> On 10/30/2018 10:03 PM, Stephen Boyd wrote:
> > Also, those
> > numbers look like gigabits per second (Gbit/s) for the DP spec which
> > isn't exactly the same as a clk frequency. What frequency does the PLL
> > run at for these various DP link speeds?
> > 
> Could you please help with the above query from Stephen?

Can I safely assume that it matches the link rate shown on Wikipedia for
display port[1]? I.e.

 RBR (Reduced Bit Rate): 1.62 Gbit/s bandwidth per lane (162 MHz link
 symbol rate)
 HBR (High Bit Rate): 2.70 Gbit/s bandwidth per lane (270 MHz link
 symbol rate)
 HBR2 (High Bit Rate 2): 5.40 Gbit/s bandwidth per lane (540 MHz link
 symbol rate), introduced in DP 1.2
 HBR3 (High Bit Rate 3): 8.10 Gbit/s bandwidth per lane (810 MHz link
 symbol rate), introduced in DP 1.3

So then they're MHz but the table is written in kHz when it should be
written in Hz. Either way, the table can be removed and then we just
need to fix the DP PHY PLL code to accept Hz instead of kHz.

[1] https://en.wikipedia.org/wiki/DisplayPort#Main_link