linux-kernel - Re: [PATCH v3 3/5] dt-bindings: sdhci-omap: Add bindings for the sdhci-omap controller

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Date:   Tue, 29 Aug 2017 16:50:22 +0530
From:   Kishon Vijay Abraham I <kishon@...com>
To:     Ulf Hansson <ulf.hansson@...aro.org>
CC:     Adrian Hunter <adrian.hunter@...el.com>,
        Rob Herring <robh+dt@...nel.org>,
        Tony Lindgren <tony@...mide.com>, Sekhar Nori <nsekhar@...com>,
        Russell King <linux@...linux.org.uk>,
        Ravikumar Kattekola <rk@...com>,
        "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        linux-omap <linux-omap@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v3 3/5] dt-bindings: sdhci-omap: Add bindings for the
 sdhci-omap controller

Hi Uffe,

On Thursday 24 August 2017 04:59 PM, Ulf Hansson wrote:
> On 23 August 2017 at 15:56, Kishon Vijay Abraham I <kishon@...com> wrote:
>> Hi Uffe,
>>
>> On Wednesday 23 August 2017 06:37 PM, Ulf Hansson wrote:
>>> On 23 August 2017 at 07:42, Kishon Vijay Abraham I <kishon@...com> wrote:
>>>> Add binding for the TI's sdhci-omap controller. This now includes only
>>>> a subset of properties documented in ti-omap-hsmmc.txt but will eventually
>>>> include all the properties.
>>>>
>>>> Signed-off-by: Kishon Vijay Abraham I <kishon@...com>
>>>> ---
>>>> Changes from v2:
>>>> *) Fixed example to use the updated compatible
>>>>
>>>> Changes from v1:
>>>> *) Create a new sdhci-omap.txt document for TI's sdhci-omap controller instead
>>>>    of using the ti-omap-hsmmc.txt as suggested by Tony
>>>>  .../devicetree/bindings/mmc/sdhci-omap.txt         | 22 ++++++++++++++++++++++
>>>>  1 file changed, 22 insertions(+)
>>>>  create mode 100644 Documentation/devicetree/bindings/mmc/sdhci-omap.txt
>>>>
>>>> diff --git a/Documentation/devicetree/bindings/mmc/sdhci-omap.txt b/Documentation/devicetree/bindings/mmc/sdhci-omap.txt
>>>> new file mode 100644
>>>> index 000000000000..139695ad2d58
>>>> --- /dev/null
>>>> +++ b/Documentation/devicetree/bindings/mmc/sdhci-omap.txt
>>>> @@ -0,0 +1,22 @@
>>>> +* TI OMAP SDHCI Controller
>>>> +
>>>> +Refer to mmc.txt for standard MMC bindings.
>>>> +
>>>> +Required properties:
>>>> +- compatible: Should be "ti,dra7-sdhci" for DRA7 and DRA72 controllers
>>>> +- ti,hwmods: Must be "mmc<n>", <n> is controller instance starting 1
>>>> +
>>>> +Optional properties:
>>>> +- ti,dual-volt: boolean, supports dual voltage cards
>>>> +- ti,non-removable: non-removable slot (like eMMC)
>>>> +
>>>> +Example:
>>>> +       mmc1: mmc@...809c000 {
>>>> +               compatible = "ti,dra7-sdhci";
>>>> +               reg = <0x4809c000 0x400>;
>>>> +               ti,hwmods = "mmc1";
>>>> +               ti,dual-volt;
>>>> +               bus-width = <4>;
>>>> +               vmmc-supply = <&vmmc>; /* phandle to regulator node */
>>>> +               ti,non-removable;
>>>> +       };
>>>> --
>>>> 2.11.0
>>>>
>>>
>>> I am wondering a bit on the long term plan here.
>>>
>>> Ideally at some point in future, we would like to remove the old
>>> omap_hsmmc driver, but from compatible string point of view, that
>>> means we first needs to deprecate the old ones for a while. Right?
>>
>> right but sdhci-omap is still lacking features that was present in omap_hsmmc
>> like context save/restore, SDIO support etc. I think we should deprecate
>> omap_hsmmc compatible once we add all the features in sdhci-omap?
>>>
>>> That said, what is then the reason to why we should bring over the
>>> existing omap_hsmmc bindings to the sdhci-omap bindings?
>>
>> This is mainly for old dt compatibility. Even after removing the omap_hsmmc
>> driver, users should still be able to use newer kernel with their existing dtbs.
> 
> I guess we have two options.
> 
> 1) Allow us to invent and use new bindings - and a new compatible.
> When everything is implemented in sdhci-omap, we can deprecate the old
> omap_hsmmc driver and its corresponding compatible/bindings. At some
> point later we can remove the legacy driver/bindings altogether - of
> course that might take a while. This option allows us to re-think some
> of the old bindings and really clean up some if its related code. For
> example, I think "ti,dual-volt" is a bad binding. Instead it would be
> better to use the existing mmc bindings about which speed mode the
> controller/board supports (as the voltage level comes with it).
> 
> 2) Invent only a new compatible, but stick to use the old omap hsmmc
> bindings and thus also deploy the similar code dealing with them. When
> everything is implemented move the old omap_hsmmc compatibles into the
> new sdhci-omap driver and them remove the old omap_hsmmc driver. At
> that point we could also deprecate the old omap hsmmc compatibles, but
> to me that is rather pointless.
> 
> The two options has different advantages, feel free to pick any of them!

Okay. I'll send a new version with option '1' (new compatible/new bindings).

And when we deprecate the omap_hsmmc driver (some time later), we'll add
support for the legacy bindings in sdhci-omap driver (so that old dtbs continue
to work). Tony, are you okay with this?

Thanks
Kishon