Date:   Fri, 22 May 2020 08:57:06 -0700
From:   Sowjanya Komatineni <skomatineni@...dia.com>
To:     Thierry Reding <thierry.reding@...il.com>
CC:     Dmitry Osipenko <digetx@...il.com>,
        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 5/22/20 8:26 AM, Thierry Reding wrote:
> On Fri, May 22, 2020 at 08:22:47AM -0700, Sowjanya Komatineni wrote:
>> On 5/22/20 5:34 AM, Thierry Reding wrote:
>>> On Fri, May 22, 2020 at 03:18:40PM +0300, Dmitry Osipenko wrote:
>>>> 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.
>> Both of these quirks are different.
>>
>> PADCALIB is for auto calibration support.
>>
>> NEEDS_PAD_CONTROL is for SoC having separate 3V3 and 1V8 pads where they
>> have pad state selection and also diff drive strengths apply based on 3V3
>> and 1V8 which are used only when auto cal is not used/failed.
> Great, would you mind sending out a patch that describes their uses
> somewhere above their definitions? It'd be good to have this documented
> in the code in case this ever comes up again.
>
> Thierry
OK, Will send

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