linux-kernel - Re: [PATCH 4/6] phy: qcom-qmp-combo: fix broken power on

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Message-ID: <Y3Hyt9xNQEjifDUY@hovoldconsulting.com>
Date:   Mon, 14 Nov 2022 08:48:07 +0100
From:   Johan Hovold <johan@...nel.org>
To:     Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Cc:     Johan Hovold <johan+linaro@...nel.org>,
        Vinod Koul <vkoul@...nel.org>, Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        linux-arm-msm@...r.kernel.org, linux-phy@...ts.infradead.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH 4/6] phy: qcom-qmp-combo: fix broken power on

On Sat, Nov 12, 2022 at 09:15:43AM +0300, Dmitry Baryshkov wrote:
> On 11/11/2022 11:42, Johan Hovold wrote:
> > The PHY is powered on during phy-init by setting the SW_PRWDN bit in the
> 
> Nit: SW_PWRDN
> 
> > COM_POWER_DOWN_CTRL register and then setting the same bit in the in the
> > PCS_POWER_DOWN_CONTROL register that belongs to the USB part of the
> > PHY.
> > 
> > Currently, whether power on succeeds depends on probe order and having
> > the USB part of the PHY be initialised first. In case the DP part of the
> > PHY is instead initialised first, the intended power on of the USB block
> > results in a corrupted DP_PHY register (e.g. DP_PHY_AUX_CFG8).
> > 
> > Add a pointer to the USB part of the PHY to the driver data and use that
> > to power on the PHY also if the DP part of the PHY is initialised first.
> > 
> > Fixes: 52e013d0bffa ("phy: qcom-qmp: Add support for DP in USB3+DP combo phy")
> > Cc: stable@...r.kernel.org	# 5.10
> > Signed-off-by: Johan Hovold <johan+linaro@...nel.org>
> 
> I can only hope that at some point in your cleanup this hack is going to 
> be removed.
> Nevertheless, I don't see a good way to do this at this moment. Thus:

Not sure why you're calling this a hack. This is how the hardware works
and pretending that this PHY is some kind of MFD with completely
independent components is partly what resulted in this mess.

Accessing the USB registers by means of a hard-coded index in the PHY
array as is done in the runtime PM callbacks is a hack (see patch 5/6),
adding a dedicated pointer is not.

> Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>

Johan