Re: [PATCH v2 2/3] dt-bindings: mmc: Add a new property disable-cqe-dcmd.

Christoph Müllner
2019-03-12T17:16:40Z

> On 12.03.2019, at 18:10, Heiko Stübner <heiko@sntech.de> wrote:
>
> Hi Christoph,
>
> Am Dienstag, 12. März 2019, 15:46:44 CET schrieb Christoph Müllner:
>>> On 12.03.2019, at 14:17, Heiko Stuebner <heiko@sntech.de> wrote:
>>>
>>> Am Freitag, 8. März 2019, 14:10:45 CET schrieb Christoph Müllner:
>>>>> On 08.03.2019, at 13:46, Adrian Hunter <adrian.hunter@intel.com> wrote:
>>>>>
>>>>> On 7/03/19 10:43 AM, Christoph Muellner wrote:
>>>>>> This patch documents the new property disable-cqe-dcmd
>>>>>> for the Arasan eMMC 5.1 driver.
>>>>>>
>>>>>> Signed-off-by: Christoph Muellner
>>>>>> <christoph.muellner@theobroma-systems.com> Signed-off-by: Philipp
>>>>>> Tomsich <philipp.tomsich@theobroma-systems.com> ---
>>>>>> Documentation/devicetree/bindings/mmc/arasan,sdhci.txt | 4 ++++
>>>>>> 1 file changed, 4 insertions(+)
>>>>>>
>>>>>> diff --git a/Documentation/devicetree/bindings/mmc/arasan,sdhci.txt
>>>>>> b/Documentation/devicetree/bindings/mmc/arasan,sdhci.txt index
>>>>>> 1edbb049cccb..ec699bf98b7c 100644
>>>>>> --- a/Documentation/devicetree/bindings/mmc/arasan,sdhci.txt
>>>>>> +++ b/Documentation/devicetree/bindings/mmc/arasan,sdhci.txt
>>>>>>
>>>>>> @@ -44,6 +44,10 @@ Optional Properties:
>>>>>> properly. Test mode can be used to force the controller to function.
>>>>>>
>>>>>> - xlnx,int-clock-stable-broken: when present, the controller always
>>>>>> reports
>>>>>>
>>>>>> that the internal clock is stable even when it is not.
>>>>>>
>>>>>> + - disable-cqe-dcmd: The eMMC 5.1 standard specifies direct commands
>>>>>> (DCMDs) + as part of the command queue engine (CQE). On controllers
>>>>>> with a CQHCI, + such as the Arasan eMMC 5.1 host controller, the
>>>>>> driver has to enable DCMDs. + This is done unless disable-cqe-dcmd
>>>>>> is specified.
>>>
>>> This needs a rewording please. See below for hw-description vs. driver, so
>>> the description should be centered around why this is a property of the hw
>>> [like faulty controller implementation or whatever]
>>
>> I understand, that you prefer a HW-specific name for a property
>> over one, that explains the actual effect.
>
> Actually I think the property-name is just fine :-) .
>
> The description might profit from a rewording though. Aka not driver-
> centric but hw-centric, describing why some controllers may need the
> option to disable these dcmds (controller bugs or whatever).

Ah, ok. Now I understand what you mean.
Will do for v3.

Thanks,
Christoph

>
>
> Heiko
>
>
>
>> However, using disable-<feature> (which is always a directive for the driver
>> and not a HW description) is not uncommon:
>>
>> * disable-wp should be "no-wp-line-connection"
>> * disable-over-current -> "no-over-current-line-connection"
>> * srp-disable -> "not-existing-srp-implementation"
>> * ...
>>
>> But I don't mind using something else.
>> Would "broken-cqe-dcmd" (like broken-cd or broken-flash-reset) be ok?
>> Or other suggestions?
>>
>> Also I'd like to mention, that my first implementation was
>> "supports-cqe-dcmd". I guess that would be a good choice, if it would have
>> been there
>> from the beginning. Introducing it now, would silently disable DCMD
>> for existing DTBs. Therefore I went on to "disable-cqe-dcmd".
>>
>>>>> If "supports-cqe" is in mmc.txt, should "disable-cqe-dcmd" be there
>>>>> also?
>>>>
>>>> The file mmc.txt says on top:
>>>> "These properties are common to multiple MMC host controllers".
>>>> As my patchset introduces "disable-cqe-dcmd" just for sdhci-of-arasan,
>>>> I would say it should not go into that file.
>>>>
>>>> Also I wonder why "supports-cqe" is in mmc.txt, because
>>>> only sdhci-tegra.c is evaluating that property.
>>>> So I would expect it to be documented in
>>>> Documentation/devicetree/bindings/mmc/nvidia,tegra20-sdhci.txt
>>>>
>>>> However, I see that "disable-cqe-dcmd" could go into other drivers as
>>>> well.
>>>> But is this enough to document it in mmc.txt?
>>>
>>> Devicetree is always about describing the hardware capabilites and never
>>> about the actual nitty-gritty of driver implementation, aka it is not
>>> meant
>>> as a space for hardware-independent config-settings or such.
>>>
>>> As for only tegra evaluating this, is probably because it is still so new,
>>> like january 2019 and Rob explicitly suggested it becoming common [0],
>>> which suggests that the disable-cqe-dcmds should probably also be common.
>> So mmc.txt lists "standardised" names for properties to reduce the risk
>> of having similar, but distinct names for different MMC drivers.
>> So whenever you want to introduce a new property for a driver,
>> check if there isn't already something defined in mmc.txt.
>>
>> When seeing it this way, it clearly makes sense to have the property there.
>>
>> Thanks,
>> Christoph

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