linux-kernel - Re: [PATCH v1] clk: qcom: gcc-sc8280xp: add cxo as parent for gcc_ufs_ref_clkref

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Message-ID: <20221103024949.lw4g2tavk7uw5xt4@builder.lan>
Date:   Wed, 2 Nov 2022 21:49:49 -0500
From:   Bjorn Andersson <andersson@...nel.org>
To:     Johan Hovold <johan@...nel.org>,
        Shazad Hussain <quic_shazhuss@...cinc.com>
Cc:     Stephen Boyd <sboyd@...nel.org>, bmasney@...hat.com,
        Andy Gross <agross@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...ainline.org>,
        Michael Turquette <mturquette@...libre.com>,
        linux-arm-msm@...r.kernel.org, linux-clk@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] clk: qcom: gcc-sc8280xp: add cxo as parent for
 gcc_ufs_ref_clkref_clk

On Wed, Nov 02, 2022 at 10:26:13AM +0100, Johan Hovold wrote:
> On Wed, Nov 02, 2022 at 02:15:26PM +0530, Shazad Hussain wrote:
> > On 11/2/2022 1:43 PM, Johan Hovold wrote:
> 
> > > Right, but if the PHYs really requires CX and it is not an ancestor of
> > > the refclk then this should be described by the binding (and not be
> > > hidden away in the clock driver).
> 
> > This makes sense, will be posting v2 post for the same.
> > I assume this should use the Fixes tag then !
> 
> Yeah, I guess to you can add a fixes tag for the commits adding support
> for sc8280xp to the UFS PHY binding and driver.
> 
> But please do check with the hardware documentation first so we get this
> right this time.
> 
> I've already asked Bjorn to see what he can dig out as it is still not
> clear how the two "card" refclocks (GCC_UFS_CARD_CLKREF_CLK and
> GCC_UFS_1_CARD_CLKREF_CLK) are supposed to be used.
> 

We've come full circle and Shazad's patch came from that discussion :)

In line with the downstream dts, we have GCC_UFS{,_1}_CARD_CLKREF_CLK
providing a reference clock to the two phys. Then GCC_UFS_REF_CLKREF_CLK
feeds the UFS refclock pads (both of them), which connect to the memory
device(s).

In other words, GCC_UFS{,_1}_CARD_CLKREF_CLK should be "ref" in
respective phy.

GCC_UFS_REF_CLKREF_CLK is the clock to the devices, but as we don't
represent the memory device explicitly it seems suitable to use as
"ref_clk" in the ufshc nodes - which would then match the special
handling of the "link clock" in the UFS driver.

All three clocks are sourced off the CXO pad, so I would like this patch
to cover at least all of these. And

Fixes: d65d005f9a6c ("clk: qcom: add sc8280xp GCC driver")

seems to be in order for such patch.

@Johan, would you mind writing a dts patch flipping the clocks around
and Shazad can update this patch?

Regards,
Bjorn