Date:   Fri, 22 May 2020 15:18:40 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Thierry Reding <thierry.reding@...il.com>,
        Sowjanya Komatineni <skomatineni@...dia.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

22.05.2020 15:13, Thierry Reding пишет:
> On Wed, May 20, 2020 at 09:09:33AM -0700, Sowjanya Komatineni wrote:
>>
>> On 5/20/20 4:26 AM, Ulf Hansson wrote:
>>> On Wed, 20 May 2020 at 04:00, Dmitry Osipenko <digetx@...il.com> wrote:
>>>> 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@...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.
>>>>>> 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.
>>
>> Drive strengths we program here when auto calibration fails are recommended
>> values based on pre-SI circuit analysis and characterized across PVT.
>>
>> So,  these fail safe values are same for all boards of specific SoC as all
>> platform designs follow the design guidelines.
>>
>>>> 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.
>>> For now I will keep $subject patch applied, but please tell me if I
>>> should drop it so we can start over.
>>>
>>> In any case, I would appreciate it if someone could have a stab at
>>> converting sdhci and tegra DT bindings to yaml.
>>>
>>> Kind regards
>>> Uffe
>>
>> HI Uffe,
>>
>> Please drop $subject patch. Will send patch that allows parsing for these
>> properties only for SoC where auto cal is enabled as that's where driver
>> needs these properties.
>>
>> So with this fix, warning will not show up on systems where autocal is not
>> enabled.
> 
> Yes, I think that's a better option. Have we ensured that on all systems
> where autocal is enabled these values are part of the device tree? Just
> making sure that we're not going to have some generation still spit out
> these warnings because we forgot to update the device tree.
> 
> For example I see that we set NVQUIRK_HAS_PADCALIB but I don't see these
> properties being set in arch/arm/boot/dts/tegra30.dtsi. Can you add a
> patch that also adds the properties for Tegra30?

I don't see the warnings on T30 using Sowjanya's patch which checks for
NVQUIRK_NEEDS_PAD_CONTROL and not NVQUIRK_HAS_PADCALIB.

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