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Subject: Re: [PATCH v1] sdhci: tegra: Remove warnings about missing
 device-tree properties
From:   Sowjanya Komatineni <skomatineni@nvidia.com>
To:     Dmitry Osipenko <digetx@gmail.com>,
        Thierry Reding <thierry.reding@gmail.com>
CC:     Ulf Hansson <ulf.hansson@linaro.org>,
        Jonathan Hunter <jonathanh@nvidia.com>,
        Adrian Hunter <adrian.hunter@intel.com>,
        "linux-mmc@vger.kernel.org" <linux-mmc@vger.kernel.org>,
        linux-tegra <linux-tegra@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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Message-ID: <c7469c16-f6f1-f9c0-566f-3b1d3774f130@nvidia.com>
Date:   Tue, 19 May 2020 12:07:28 -0700
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On 5/19/20 11:41 AM, Sowjanya Komatineni wrote:
>
> On 5/19/20 11:34 AM, Sowjanya Komatineni wrote:
>>
>> On 5/19/20 9:33 AM, Dmitry Osipenko wrote:
>>> 19.05.2020 19:24, Thierry Reding =D0=BF=D0=B8=D1=88=D0=B5=D1=82:
>>>> On Tue, May 19, 2020 at 05:05:27PM +0300, Dmitry Osipenko wrote:
>>>>> 19.05.2020 10:28, Ulf Hansson =D0=BF=D0=B8=D1=88=D0=B5=D1=82:
>>>>>> On Sat, 16 May 2020 at 17:44, Dmitry Osipenko <digetx@gmail.com>=20
>>>>>> wrote:
>>>>>>> Several people asked me about the MMC warnings in the KMSG log and
>>>>>>> I had to tell to ignore them because these warning are=20
>>>>>>> irrelevant to
>>>>>>> pre-Tegra210 SoCs.
>>>>>> Why are the warnings irrelevant?
>>>>> That's what the DT binding doc says [1].
>>>>>
>>>>> [1]
>>>>> https://www.kernel.org/doc/Documentation/devicetree/bindings/mmc/nvid=
ia%2Ctegra20-sdhci.txt=20
>>>>>
>>>>>
>>>>> Although, looking at the driver's code and TRM docs, it seems that=20
>>>>> all
>>>>> those properties are really irrelevant only to the older Terga20=20
>>>>> SoC. So
>>>>> the binding doc is a bit misleading.
>>>>>
>>>>> Nevertheless, the binding explicitly says that the properties are
>>>>> optional, which is correct.
>>>> Optional only means that drivers must not fail if these properties
>>>> aren't found, it doesn't mean that the driver can't warn that they
>>>> are missing.
>>>>
>>>> Quite possibly the only reason why they were made optional is because
>>>> they weren't part of the bindings since the beginning. Anything added
>>>> to a binding after the first public release has to be optional by
>>>> definition, otherwise DT ABI wouldn't be stable.
>>>>
>>>> I think these warnings were added on purpose, though I also see that
>>>> there are only values for these in device tree for Tegra186 and=20
>>>> Tegra194
>>>> but not Tegra210 where these should also be necessary.
>>
>> dt binding doc we have is common for MMC, SD and SDIO of all Tegras.=20
>> Its not mandatory to have both 3v3 and 1v8 in device tree as based on=20
>> signal mode.
>>
>> As these driver strengths are SoC specific, they are part of Tegra=20
>> SoC specific device tree where same values will be applicable to all=20
>> Tegra SoC specific platforms.
>>
>> Based on interface usage on platform, we use one or both of them like=20
>> sdcard supports dual voltage and we use both 3V3 and 1V8 but if same=20
>> interface is used for WIFI SD we use 1V8 only.
>>
>> So made these dt properties as optional.
>>
>> Other reason they are optional is, Tegra210 and prior has drive=20
>> strength settings part of apb_misc and Tegra186 and later has driver=20
>> strengths part of SDMMC controller. So,
>>
>> - Pinctrls "sdmmc-3v3-drv" and "sdmmc-1v8-drv" for driver strengths=20
>> are applicable for Tegra210 and prior.
>> - dt properties pad-autocal-pull-up/down-offset-1v8/3v3-timeout are=20
>> for T186 onwards for driver strengths
>>
>> Looks like dt binding doc need fix to clearly document these based on=20
>> SoC or agree with Yaml we can conditionally specify pinctrl or dt=20
>> properties based on SoC dependent.
>>
>>
>>>> Adding Sowjanya who wrote this code. Perhaps she can clarify why the
>>>> warnings were added. If these values /should/ be there on a subset of
>>>> Tegra, then I think we should keep them, or add them again, but=20
>>>> perhaps
>>>> add a better way of identifying when they are necessary and when it is
>>>> safe to work without them.
>>>>
>>>> That said, looking at those checks I wonder if they are perhaps just
>>>> wrong. Or at the very least they seem redundant. It looks to me like
>>>> they can just be:
>>>>
>>>> =C2=A0=C2=A0=C2=A0=C2=A0if (tegra_host->pinctrl_state_XYZ =3D=3D NULL)=
 {
>>>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 ...
>>>> =C2=A0=C2=A0=C2=A0=C2=A0}
>>>>
>>>> That !IS_ERR(...) doesn't seem to do anything. But in that case, it's
>>>> also obvious why we're warning about them on platforms where these
>>>> properties don't exist in DT.
>>
>> As drive strengths are through dt properties for T186 and later and=20
>> thru pinctrl for T210 and prior, driver first checks for dt autocal=20
>> timeout pull-up/down properties and if they are not found, it then=20
>> checks for presence of pinctrl_state_xyx_drv only when valid=20
>> pinctrl_state_xyz is present.
>>
>> Driver expects either pinctrl or dt properties and shows warning when=20
>> neither of them are present as its mandatory to use fixed driver=20
>> strengths when auto calibration fails.
>>
>> =C2=A0=C2=A0=C2=A0 err =3D device_property_read_u32(host->mmc->parent,
>> =C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 "nvidia,pad-aut=
ocal-pull-down-offset-3v3-timeout",
>> =C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 &autocal->pull_=
down_3v3_timeout);
>> =C2=A0=C2=A0=C2=A0 if (err) {
>> =C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 if (!IS_ERR(tegra_host->pinctrl_st=
ate_3v3) &&
>> =C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 (tegra_host->pi=
nctrl_state_3v3_drv =3D=3D NULL))
>> =C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 pr_warn("%s: Mi=
ssing autocal timeout 3v3-pad drvs\n",
>> =C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2=
=A0 mmc_hostname(host->mmc));
>> =C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 autocal->pull_down_3v3_timeout =3D=
 0;
>> =C2=A0=C2=A0=C2=A0 }
>>
>>>>
>>>> So I think we either need to add those values where appropriate so=20
>>>> that
>>>> the warning doesn't show, or we need to narrow down where they are
>>>> really needed and add a corresponding condition.
>>>>
>>>> But again, perhaps Sowjanya can help clarify if these really are only
>>>> needed on Tegra210 and later or if these also apply to older chips.
>>> Either way will be cleaner to convert the DT binding to YAML rather=20
>>> than
>>> clutter the driver, IMO.
>>>
>>
>>
>>
> Auto calibration is present from Tegra30 onward and looking into=20
> change where autocalibration was added to sdhci driver somehow it was=20
> enabled only for T30/T210/T186/T194.
>
> tegra_sdhci_parse_pad_autocal_dt() was added when auto-calibration was=20
> added to driver and I see this dt parse is being done irrespective of=20
> NVQUIRK_HAS_PADCALIB quirk so even on platforms without auto cal=20
> enabled in driver, these messages shows up.
>
> This should be fixed in driver to allow=20
> tegra_sdhci_parse_pad_autocal_dt() only when NVQUIRK_HAS_PADCALIB is=20
> set to avoid dt parsing to happen on platforms that don't have auto=20
> cal enabled.

Warning on missing drive strengths when auto cal is enabled should be=20
present as we should switch to fixed recommended drive strengths when=20
auto cal fails.

So probably proper fix should be

- allow tegra_sdhci_parse_pad_autocal_dt() only when=20
NVQUIRK_HAS_PADCALIB is set

- current driver sets NVQUIRK_HAS_PADCALIB for T30 as well so need to=20
add pinctrls "sdmmc-3v3-drv" and "sdmmc-1v8-drv" to Tegra30 device tree.

- Keep warning message of missing auto cal timeouts as its mandatory to=20
use fixed recommended driver strengths when auto cal fails.