linux-kernel - Re: [PATCH v2 09/14] phy: qcom-qmp-pcie: replace power-down delay

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Date:   Wed, 12 Oct 2022 23:40:48 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Johan Hovold <johan+linaro@...nel.org>,
        Vinod Koul <vkoul@...nel.org>
Cc:     Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...ainline.org>,
        Kishon Vijay Abraham I <kishon@...com>,
        linux-arm-msm@...r.kernel.org, linux-phy@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 09/14] phy: qcom-qmp-pcie: replace power-down delay

On 12/10/2022 11:12, Johan Hovold wrote:
> The power-down delay was included in the first version of the QMP driver
> as an optional delay after powering on the PHY (using
> POWER_DOWN_CONTROL) and just before starting it. Later changes modified
> this sequence by powering on before initialising the PHY, but the
> optional delay stayed where it was (i.e. before starting the PHY).
> 
> The vendor driver does not use a delay before starting the PHY and this
> is likely not needed on any platform unless there is a corresponding
> delay in the vendor kernel init sequence tables (i.e. in devicetree).
> 
> But as the vendor kernel do have a 1 ms delay *after* starting the PHY
> and before starting to poll the status it is possible that later
> contributors have simply not noticed that the mainline power-down delay
> is not equivalent.
> 
> As the current delay before even starting the PHY is pretty much
> pointless and likely a mistake, move the delay after starting the PHY
> which avoids a few iterations of polling and speeds up startup by 1 ms
> (the poll loop otherwise takes about 1.8 ms).
> 
> Note that MSM8998 has never used a power-down delay so add a flag to
> skip the delay in case starting the PHY is faster on MSM8998. This can
> be removed after someone takes a measurement.
> 
> Signed-off-by: Johan Hovold <johan+linaro@...nel.org>
> ---
>   drivers/phy/qualcomm/phy-qcom-qmp-pcie.c | 33 +++++-------------------
>   1 file changed, 6 insertions(+), 27 deletions(-)
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>

-- 
With best wishes
Dmitry