linux-kernel - Re: [PATCH v2 11/11] phy: qcom-qmp-pcie: drop bogus register update

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Message-ID: <YzWSCI7uGnWVxKPp@hovoldconsulting.com>
Date:   Thu, 29 Sep 2022 14:39:36 +0200
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@...ainline.org>,
        Kishon Vijay Abraham I <kishon@...com>,
        Neil Armstrong <neil.armstrong@...aro.org>,
        linux-arm-msm@...r.kernel.org, linux-phy@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 11/11] phy: qcom-qmp-pcie: drop bogus register update

On Thu, Sep 29, 2022 at 01:18:05PM +0300, Dmitry Baryshkov wrote:
> On Thu, 29 Sept 2022 at 12:29, Johan Hovold <johan+linaro@...nel.org> wrote:
> >
> > Since commit 0d58280cf1e6 ("phy: Update PHY power control sequence") the
> > PHY is powered on before configuring the registers and only the MSM8996
> > PCIe PHY, which includes the POWER_DOWN_CONTROL register in its PCS
> > initialisation table, may possibly require a second update afterwards.
> >
> > To make things worse, the POWER_DOWN_CONTROL register lies at a
> > different offset on more recent SoCs so that the second update, which
> > still used a hard-coded offset, would write to an unrelated register
> > (e.g. a revision-id register on SC8280XP).
> >
> > As the MSM8996 PCIe PHY is now handled by a separate driver, simply drop
> > the bogus register update.
> >
> > Fixes: e4d8b05ad5f9 ("phy: qcom-qmp: Use proper PWRDOWN offset for sm8150 USB") added support
> 
> Unless somebody confirms that this write is not needed on 8998 and
> sdm845, I'd prefer a two stage fix here:
> - changing this to write to proper register (and maybe moving to the
> top of patch series, as we'd want to backport this to the last few
> kernels)

It already is the "proper" register for the v2 platforms that may
conceivably need it it. For the rest it is clearly just broken.

And I don't think this needs to block the rest of the series. That's
why I moved it last. If we decide to backport this we have other context
changes in -next to handle anyway.

> - dropping the write completely.

But sure, doing it in two steps is a possibility.

> Meanwhile I'll try testing this patchset on rb3 and checking whether
> it makes any difference or not.

Thanks for doing that.

Johan