linux-kernel - Re: [PATCH 00/16] Fix Qcom UFS PHY clocks

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Message-ID: <20231214103907.GL2938@thinkpad>
Date:   Thu, 14 Dec 2023 16:09:07 +0530
From:   Manivannan Sadhasivam <mani@...nel.org>
To:     Johan Hovold <johan@...nel.org>
Cc:     Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
        andersson@...nel.org, konrad.dybcio@...aro.org, vkoul@...nel.org,
        sboyd@...nel.org, mturquette@...libre.com, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, conor+dt@...nel.org,
        linux-arm-msm@...r.kernel.org, linux-phy@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-clk@...r.kernel.org,
        devicetree@...r.kernel.org
Subject: Re: [PATCH 00/16] Fix Qcom UFS PHY clocks

On Thu, Dec 14, 2023 at 11:15:34AM +0100, Johan Hovold wrote:
> On Thu, Dec 14, 2023 at 02:40:45PM +0530, Manivannan Sadhasivam wrote:
> 
> > This series fixes the clocks supplied to QMP PHY IPs in the Qcom SoCs. All
> > of the Qcom SoCs except MSM8996 require 3 clocks for QMP UFS:
> > 
> > * ref - 19.2MHz reference clock from RPM/RPMh
> > * ref_aux - Auxiliary reference clock from GCC
> > * qref - QREF clock from GCC or TCSR (TCSR since SM8550)
> > 
> > MSM8996 only requires 'ref' and 'qref' clocks.
> > 
> > Hence, this series fixes the binding, DT and GCC driver to reflect the
> > actual clock topology.
> 
> Is this based on documentation for all the SoCs or on inference from the
> current (upstream and downstream) devicetrees?
> 

It is based on the internal documentation. Even downstream devicetrees are
wrong. I should've mentioned it in the cover letter.

> Are you sure that you should not just describe that some of these UFS
> reference clocks are sourced from CXO in the clock driver instead?
> 

I don't get your comment fully. Could you please elaborate?

> Take a look at commits
> 
> 	f446022b932a ("arm64: dts: qcom: sc8280xp: fix UFS reference clocks")
> 	f6abcc21d943 ("clk: qcom: gcc-sc8280xp: add cxo as parent for three ufs ref clks")
> 

Btw, these commits are not accurate. In all the SoCs before SM8550, reference
clock for the UFS device comes from the UFS controller. There is a dedicated
register in UFSHC memory map that is being toggled by the driver to
enable/disable reference clock for the UFS device.

Since SM8550, reference clock is directly sourced from RPMh. I'm preparing a
series to fix it.

Unfortunately, this information is not depicted correctly in the downstream
devicetrees.

- Mani

> Johan
> 

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