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

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Date:   Thu, 24 Aug 2017 13:29:39 +0200
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Kishon Vijay Abraham I <kishon@...com>
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

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!

Kind regards
Uffe