Message-ID: <CAPDyKFrnKso=5oBsmHYAOQV_0jy9aB9JROWESEV4pdUsPi4dFg@mail.gmail.com>
Date:   Mon, 25 May 2020 10:47:39 +0200
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Thierry Reding <thierry.reding@...il.com>,
        Sowjanya Komatineni <skomatineni@...dia.com>,
        Dmitry Osipenko <digetx@...il.com>
Cc:     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 Fri, 22 May 2020 at 14:14, Thierry Reding <thierry.reding@...il.com> wrote:
>
> 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?
>

Patch dropped, thanks!

Kind regards
Uffe

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