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

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Date:   Thu, 26 Jan 2023 15:29:36 +0000
From:   Bryan O'Donoghue <bryan.odonoghue@...aro.org>
To:     Stephan Gerhold <stephan@...hold.net>
Cc:     agross@...nel.org, andersson@...nel.org, konrad.dybcio@...aro.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 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.

---
bod