linux-kernel - Re: [PATCH v2 2/2] mmc: sdhci-omap: Workaround errata regarding SDR104/HS200 tuning failures (i929)

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Date:   Mon, 7 Jan 2019 16:05:07 +0530
From:   Faiz Abbas <faiz_abbas@...com>
To:     Olof Johansson <olof@...om.net>
CC:     Eduardo Valentin <edubezval@...il.com>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Kishon <kishon@...com>, Keerthy <j-keerthy@...com>,
        Zhang Rui <rui.zhang@...el.com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Santosh Shilimkar <ssantosh@...nel.org>,
        Tony Lindgren <tony@...mide.com>
Subject: Re: [PATCH v2 2/2] mmc: sdhci-omap: Workaround errata regarding
 SDR104/HS200 tuning failures (i929)

Hi Olof,

On 05/01/19 6:27 AM, Olof Johansson wrote:
> On Wed, Jan 2, 2019 at 9:58 PM Faiz Abbas <faiz_abbas@...com> wrote:
>>
>> Hi Olof, Eduardo,
>>
>> On 03/01/19 1:26 AM, Eduardo Valentin wrote:
>>> On Wed, Jan 02, 2019 at 10:29:31AM -0800, Olof Johansson wrote:
>>>> Hi,
>>>>
>>>>
...
>>>>
>>>> This is throwing errors on builds of keystone_defconfig in next and mainline:
>>>>
>>>> http://arm-soc.lixom.net/buildlogs/next/next-20190102/buildall.arm.keystone_defconfig.log.passed
>>>>
>>>> WARNING: unmet direct dependencies detected for TI_SOC_THERMAL
>>>>   Depends on [n]: THERMAL [=y] && (ARCH_HAS_BANDGAP [=n] ||
>>>> COMPILE_TEST [=n]) && HAS_IOMEM [=y]
>>>>   Selected by [y]:
>>>>   - MMC_SDHCI_OMAP [=y] && MMC [=y] && MMC_SDHCI_PLTFM [=y] && OF [=y]
>>>>
>>>> So, thermal depends on ARCH_HAS_BANDGAP, which keystone doesn't provide.
>>>>
>>>> Selecting a major framework such as THERMAL from a driver config is
>>>> likely not the right solution anyway, especially since THERMAL does
>>>> provide stubbed out versions of the functions if it's not enabled.
>>>
>>> Yeah, that seams a bit up-side-down. Can you guys give a bit more of
>>> context? Why do you need the cpu thermal zone ? From patch description,
>>> looks like you want to have your own zone then apply different tuning
>>> values based on temperature (range?). Why do you need to mess up with
>>> cpu_thermal zone? Don't you have a bandgap in the mem controller for
>>> this application?
>>>
>>
>> Thats correct. We don't have a bandgap in the MMC controller and thus we
>> have to use the cpu one to measure temperature.
>>
>> THERMAL is critical for tuning. The interface is supposed to fail if we
>> can't get temperature. So IMO we should ensure that it is present.
>>
>> I can fix this by "select TI_SOC_THERMAL if ARCH_HAS_BANDGAP" if you
>> guys agree.
> 
> Building elaborate select statements is usually fragile, once
> dependencies for TI_SOC_THERMAL changes you need to come back here to
> fixup the select.
> 
> Supposedly this driver works on keystone (or does it?), it doesn't

Yes. This driver works on keystone.

> actually need TI_SOC_THERMAL for basic functionality beyond tuning?
> Or, at least, it needs to fall back to a reasonable behavior if it's
> unavailable on keystone.

The scenario is this. dra7 devices (omap2plus_defconfig) support tuning
which needs THERMAL and TI_SOC_THERMAL. Keystone devices don't need
thermal at all. The tuning part of the code will never be touched by the
keystone device.

In omap2plus_defconfig, THERMAL AND TI_SOC_THERMAL are modules by
default. I need them to be built-in because MMC is built-in.

> 
> Having the driver print a warning and refuse to tune to higher speeds
> is a reasonable way to do this, I think. That would carry to all
> platforms, i.e. even the ones who have TI_SOC_THERMAL and
> ARCH_HAS_BANDGAP, without adding the select.
> 

The MMC core today doesn't support a fallback to lower speeds when
tuning fails. The interface just fails. This means a bunch cards that
were working will now fail. Also, people building with olddefconfig will
get build errors because of THERMAL=m. Thus the Kconfig architecture
should automatically select the dependencies for SDHCI_OMAP in DRA7.

An "imply TI_SOC_THERMAL" is even better here. It won't force
TI_SOC_THERMAL for keystone and doesn't cause any warnings.

So I propose the following patch:

diff --git a/drivers/mmc/host/Kconfig b/drivers/mmc/host/Kconfig
index e26b8145efb3..bc61eefcb695 100644
--- a/drivers/mmc/host/Kconfig
+++ b/drivers/mmc/host/Kconfig
@@ -978,7 +978,7 @@ config MMC_SDHCI_OMAP
        tristate "TI SDHCI Controller Support"
        depends on MMC_SDHCI_PLTFM && OF
        select THERMAL
-       select TI_SOC_THERMAL
+       imply TI_SOC_THERMAL
        help
--

Thanks,
Faiz