Re: [PATCH v1] sdhci: tegra: Remove warnings about missing device-tree properties

[Ulf Hansson <ulf.hansson@linaro.org>]

On Wed, 20 May 2020 at 04:00, Dmitry Osipenko <digetx@gmail.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@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.

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