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Subject: Re: [PATCH v1] sdhci: tegra: Remove warnings about missing
 device-tree properties
To:     Sowjanya Komatineni <skomatineni@nvidia.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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From:   Dmitry Osipenko <digetx@gmail.com>
Message-ID: <d2c71267-e696-c459-fbd6-dbb5fd312ed3@gmail.com>
Date:   Wed, 20 May 2020 05:00:02 +0300
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19.05.2020 23:44, Sowjanya Komatineni пишет:
> 
> On 5/19/20 12:07 PM, Sowjanya Komatineni wrote:
>>
>> 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 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@gmail.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.
>>
>> Warning on missing drive strengths when auto cal is enabled should be
>> present as we should switch to fixed recommended drive strengths when
>> auto cal fails.
>>
>> So probably proper fix should be
>>
>> - allow tegra_sdhci_parse_pad_autocal_dt() only when
>> NVQUIRK_HAS_PADCALIB is set
>>
>> - current driver sets NVQUIRK_HAS_PADCALIB for T30 as well so need to
>> add pinctrls "sdmmc-3v3-drv" and "sdmmc-1v8-drv" to Tegra30 device tree.
> [Correction] T30 has same drive strengths to use irrespective of signal
> voltage and it doesn't have pad control. So for T3- we can update device
> tree to specify "default" pinctrl with drvup/dn settings.
>>
>> - Keep warning message of missing auto cal timeouts as its mandatory
>> to use fixed recommended driver strengths when auto cal fails.
>>
> Regarding warnings, I guess simpler and easy fix is to remove warning
> message on missing 3v3/1v8 drive strengths as pinctrl/dt properties were
> already added for T210/186/194 where we need and old device tree don't
> have them but the case where auto cal can fail is very rare.
> 
> Otherwise should update driver to allow
> tegra_sdhci_parse_pad_autocal_dt() only when NVQUIRK_HAS_PADCALIB is set
> and also within tegra_sdhci_parse_pad_autocal_dt() show warning of
> missing 3v3/1v8 settings only when NVQUIRK_NEEDS_PAD_CONTROL is set.
> 
> Thierry, please suggest if you prefer to removing warnings or fix driver
> to show warning based on PADCALIB and PAD_CONTROL quirks.

The SDIO PINCTRL drive-strengths are usually a part of the board's
default PINCTRL state, which is either preset by bootloader or by
PINCTRL driver early at a boot time.

The SDIO drive-strengths values should be board-specific and not
SoC-specific because they should depend on the electrical properties of
the board, IIUC.

If the SDIO PINCTRL states are mandatory for the SDHCI nodes in the
device-trees, then the DT binding is wrong since it says that all
properties are optional. But I think that the current binding is okay,
since today SDHCI PINCTRL drive-strengths are specified implicitly in
the device-trees, and thus, there is no real need to emit the noisy
warnings in this case.