Date:   Tue, 19 May 2020 11:41:40 -0700
From:   Sowjanya Komatineni <skomatineni@...dia.com>
To:     Dmitry Osipenko <digetx@...il.com>,
        Thierry Reding <thierry.reding@...il.com>
CC:     Ulf Hansson <ulf.hansson@...aro.org>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
        linux-tegra <linux-tegra@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1] sdhci: tegra: Remove warnings about missing
 device-tree properties


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 пишет:
>>> On Tue, May 19, 2020 at 05:05:27PM +0300, Dmitry Osipenko wrote:
>>>> 19.05.2020 10:28, Ulf Hansson пишет:
>>>>> On Sat, 16 May 2020 at 17:44, Dmitry Osipenko <digetx@...il.com> 
>>>>> 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 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/nvidia%2Ctegra20-sdhci.txt 
>>>>
>>>>
>>>> Although, looking at the driver's code and TRM docs, it seems that all
>>>> those properties are really irrelevant only to the older Terga20 
>>>> 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 
>>> 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. 
> Its not mandatory to have both 3v3 and 1v8 in device tree as based on 
> signal mode.
>
> As these driver strengths are SoC specific, they are part of Tegra SoC 
> specific device tree where same values will be applicable to all Tegra 
> SoC specific platforms.
>
> Based on interface usage on platform, we use one or both of them like 
> sdcard supports dual voltage and we use both 3V3 and 1V8 but if same 
> 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 
> strength settings part of apb_misc and Tegra186 and later has driver 
> strengths part of SDMMC controller. So,
>
> - Pinctrls "sdmmc-3v3-drv" and "sdmmc-1v8-drv" for driver strengths 
> are applicable for Tegra210 and prior.
> - dt properties pad-autocal-pull-up/down-offset-1v8/3v3-timeout are 
> for T186 onwards for driver strengths
>
> Looks like dt binding doc need fix to clearly document these based on 
> SoC or agree with Yaml we can conditionally specify pinctrl or dt 
> 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 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:
>>>
>>>     if (tegra_host->pinctrl_state_XYZ == NULL) {
>>>         ...
>>>     }
>>>
>>> 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 
> thru pinctrl for T210 and prior, driver first checks for dt autocal 
> timeout pull-up/down properties and if they are not found, it then 
> checks for presence of pinctrl_state_xyx_drv only when valid 
> pinctrl_state_xyz is present.
>
> Driver expects either pinctrl or dt properties and shows warning when 
> neither of them are present as its mandatory to use fixed driver 
> strengths when auto calibration fails.
>
>     err = device_property_read_u32(host->mmc->parent,
>             "nvidia,pad-autocal-pull-down-offset-3v3-timeout",
>             &autocal->pull_down_3v3_timeout);
>     if (err) {
>         if (!IS_ERR(tegra_host->pinctrl_state_3v3) &&
>             (tegra_host->pinctrl_state_3v3_drv == NULL))
>             pr_warn("%s: Missing autocal timeout 3v3-pad drvs\n",
>                 mmc_hostname(host->mmc));
>         autocal->pull_down_3v3_timeout = 0;
>     }
>
>>>
>>> So I think we either need to add those values where appropriate so 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 than
>> clutter the driver, IMO.
>>
>
>
>
Auto calibration is present from Tegra30 onward and looking into change 
where autocalibration was added to sdhci driver somehow it was enabled 
only for T30/T210/T186/T194.

tegra_sdhci_parse_pad_autocal_dt() was added when auto-calibration was 
added to driver and I see this dt parse is being done irrespective of 
NVQUIRK_HAS_PADCALIB quirk so even on platforms without auto cal enabled 
in driver, these messages shows up.

This should be fixed in driver to allow 
tegra_sdhci_parse_pad_autocal_dt() only when NVQUIRK_HAS_PADCALIB is set 
to avoid dt parsing to happen on platforms that don't have auto cal enabled.

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