linux-kernel - Re: [PATCH v4 0/6] Add MSM8939 SoC support with two devices

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Date:   Thu, 26 Jan 2023 16:34:11 +0100
From:   Konrad Dybcio <konrad.dybcio@...aro.org>
To:     Bryan O'Donoghue <bryan.odonoghue@...aro.org>,
        Stephan Gerhold <stephan@...hold.net>
Cc:     agross@...nel.org, andersson@...nel.org, djakov@...nel.org,
        robh+dt@...nel.org, krzysztof.kozlowski+dt@...aro.org,
        linux-arm-msm@...r.kernel.org, linux-pm@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        benl@...areup.com, shawn.guo@...aro.org, fabien.parent@...aro.org,
        leo.yan@...aro.org, dmitry.baryshkov@...aro.org
Subject: Re: [PATCH v4 0/6] Add MSM8939 SoC support with two devices



On 26.01.2023 16:29, Bryan O'Donoghue wrote:
> On 23/01/2023 12:49, Stephan Gerhold wrote:
>>> - Adds gcc dsi1pll and dsi1pllbyte to gcc clock list.
>>>    Reviewing the silicon documentation we see dsi0_phy_pll is used to clock
>>>    GCC_BYTE1_CFG_RCGR : SRC_SEL
>>>    Root Source Select
>>>    000 : cxo
>>>    001 : dsi0_phy_pll_out_byteclk
>>>    010 : GPLL0_OUT_AUX
>>>    011 : gnd
>>>    100 : gnd
>>>    101 : gnd
>>>    110 : gnd
>>>    111 : reserved - Stephan/Bryan
>>>
>> I'm confused. Are you not contradicting yourself here? You say that
>> dsi0_phy_pll (dsi ZERO) is used to clock GCC_BYTE1_CFG_RCGR. Then why
>> do you add dsi1_phy_pll (dsi ONE) to the gcc clock list?
> 
> So my understanding of the clock tree here is that dsi0_phy_pll_out_byteclk is a legacy name.
> 
> Its perfectly possible to have DSI0 and DSI0_PHY switched off and to have DSI1/DSI1_PHY operable.
> 
> dsi0_phy_pll_out_byteclk is perhaps an unfortunate name and probably should have been renamed.
> 
>> To me this looks like a confirmation of what downstream does, that both
>> DSI byte clocks are actually sourced from the dsi0_phy and the PLL of
> 
> A better name would have been dsiX_phy_pll_out_byteclk.
I believe Stephan is just confused what the clock source of both
pairs of GCC DSI clocks are, as you're suggesting that:

phy_clock0
  |_gcc_clock0

and

phy_clock0 (yes, zero)
  |_gcc_clock1

whereas on most other SoCs the following is true:

phy_clock0
  |_gcc_clock0

phy_clock1
  |_gcc_clock_1

Konrad
> 
> ---
> bod