linux-kernel - Re: [PATCH] arm64: dts: qcom: qcm6490-fairphone-fp5: Enable UFS

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Date:   Mon, 2 Oct 2023 11:14:36 +0200
From:   Konrad Dybcio <konrad.dybcio@...aro.org>
To:     Luca Weiss <luca.weiss@...rphone.com>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Nitin Rawat <quic_nitirawa@...cinc.com>
Cc:     ~postmarketos/upstreaming@...ts.sr.ht, phone-devel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm64: dts: qcom: qcm6490-fairphone-fp5: Enable UFS



On 10/2/23 09:02, Luca Weiss wrote:
> On Fri Sep 29, 2023 at 3:12 PM CEST, Konrad Dybcio wrote:
>> On 29.09.2023 11:52, Luca Weiss wrote:
>>> Enable the UFS phy and controller so that we can access the internal
>>> storage of the phone.
>>>
>>> At the same time we need to bump the minimum voltage used for UFS VCC,
>>> otherwise it doesn't initialize properly. The new range is taken from
>>> the vcc-voltage-level property downstream.
>>>
>>> See also the following link for more information about the VCCQ/VCCQ2:
>>> https://gerrit-public.fairphone.software/plugins/gitiles/kernel/msm-extra/devicetree/+/1590a3739e7dc29d2597307881553236d492f188/fp5/yupik-idp-pm7250b.dtsi#207
>>>
>>> Signed-off-by: Luca Weiss <luca.weiss@...rphone.com>
>>> ---
>>> I'm not 100% convinced about the regulator range change. For sure with
>>> the original voltage range the UFS fails to initialize, but looking at
>>> downstream kernel during runtime (debugfs) we see the VCC voltage
>>> switches between 2.4V (idle?) and 2.952V (active?). But even with this
>>> change in mainline the regulator would always stay at 2.504V which is
>>> for sure lower than the downstream operating voltage of 2.952V. Behavior
>>> wise I don't see a difference between ~2.5V and ~2.9V.
>>>
>>> Should I just constrain the regulator here to min=max=2.952V? Or just
>>> say it's okay as-is?
>>>
>>> Depends on: https://lore.kernel.org/linux-arm-msm/20230927081858.15961-1-quic_nitirawa@quicinc.com/
>>> ---
>> There's a little funny hack inside the driver
>>
>> #if defined(CONFIG_SCSI_UFSHCD_QTI)
>>                          if (vreg->low_voltage_sup && !vreg->low_voltage_active && on)
>>                                  min_uV = vreg->max_uV;
>> #endif
>>
>> so, when the ufs is in use, it's pinned to vmax
> 
> Hi Konrad,
> 
> Are you implying I *should* or *should not* pin the voltage range to
> 2.952V-2.952V for mainline?
Neither, voltage scaling should be implemented :P

But for now, pinning it to 2.952 const is the right temporary
solution, as having working UFS is generally better than one
that can only idle in a stable manner :D

Konrad