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

[Sowjanya Komatineni]

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 ÐÐÑÐÑ:
> > > > > On Tue, May 19, 2020 at 05:05:27PM +0300, Dmitry Osipenko wrote:
> > > > > > 19.05.2020 10:28, Ulf Hansson ÐÐÑÐÑ:
> > > > > > > On Sat, 16 May 2020 at 17:44, Dmitry Osipenko <digetx@xxxxxxxxx> 
> > > > > > > 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:
> > > > >
> > > > > ÂÂÂÂif (tegra_host->pinctrl_state_XYZ == NULL) {
> > > > > ÂÂÂÂÂÂÂ ...
> > > > > ÂÂÂÂ}
> > > > >
> > > > > 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.
> > >
> > > ÂÂÂ err = device_property_read_u32(host->mmc->parent,
> > > ÂÂÂ ÂÂÂ ÂÂÂ "nvidia,pad-autocal-pull-down-offset-3v3-timeout",
> > > ÂÂÂ ÂÂÂ ÂÂÂ &autocal->pull_down_3v3_timeout);
> > > ÂÂÂ if (err) {
> > > ÂÂÂ ÂÂÂ if (!IS_ERR(tegra_host->pinctrl_state_3v3) &&
> > > ÂÂÂ ÂÂÂ ÂÂÂ (tegra_host->pinctrl_state_3v3_drv == NULL))
> > > ÂÂÂ ÂÂÂ ÂÂÂ pr_warn("%s: Missing autocal timeout 3v3-pad drvs\n",
> > > ÂÂÂ ÂÂÂ ÂÂÂ ÂÂÂ mmc_hostname(host->mmc));
> > > ÂÂÂ ÂÂÂ autocal->pull_down_3v3_timeout = 0;
> > > ÂÂÂ }
> > >
> > > > > 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.