linux-kernel - Re: [PATCH] mmc: pwrseq: add support for Marvell SD8787 chip

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Date:   Tue, 29 Nov 2016 17:53:26 +0100
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Rob Herring <robh@...nel.org>
Cc:     Matt Ranostay <matt@...ostay.consulting>,
        "linux-wireless@...r.kernel.org" <linux-wireless@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
        Tony Lindgren <tony@...mide.com>,
        Mark Rutland <mark.rutland@....com>,
        Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
Subject: Re: [PATCH] mmc: pwrseq: add support for Marvell SD8787 chip

On 29 November 2016 at 15:51, Rob Herring <robh@...nel.org> wrote:
> On Mon, Nov 28, 2016 at 9:54 AM, Ulf Hansson <ulf.hansson@...aro.org> wrote:
>> [...]
>>
>>>> +
>>>> +Example:
>>>> +
>>>> +     wifi_pwrseq: wifi_pwrseq {
>>>> +             compatible = "mmc-pwrseq-sd8787";
>>>> +             pwrdn-gpio = <&twl_gpio 0 GPIO_ACTIVE_LOW>;
>>>> +             reset-gpio = <&twl_gpio 1 GPIO_ACTIVE_LOW>;
>>>> +     }
>>>> diff --git a/Documentation/devicetree/bindings/net/wireless/marvell-sd8xxx.txt b/Documentation/devicetree/bindings/net/wireless/marvell-sd8xxx.txt
>>>> index c421aba0a5bc..08fd65d35725 100644
>>>> --- a/Documentation/devicetree/bindings/net/wireless/marvell-sd8xxx.txt
>>>> +++ b/Documentation/devicetree/bindings/net/wireless/marvell-sd8xxx.txt
>>>> @@ -32,6 +32,9 @@ Optional properties:
>>>>                so that the wifi chip can wakeup host platform under certain condition.
>>>>                during system resume, the irq will be disabled to make sure
>>>>                unnecessary interrupt is not received.
>>>> +  - vmmc-supply: a phandle of a regulator, supplying VCC to the card
>>>
>>> This is why pwrseq is wrong. You have some properties in the card node
>>> and some in pwrseq node. Everything should be in the card node.
>>
>> Put "all" in the card node, just doesn't work for MMC. Particular in
>> cases when we have removable cards, as then it would be wrong to have
>> a card node.
>
> When is there a problem with removable cards? The connector is
> standard and everything needed (CD, VMMC, VDDIO, etc.) is defined in
> the host controller node. If that isn't sufficient, then we should
> start defining a connector node.

I probably didn't get your point. Anyway, let's try again.

I don't see any problems with removable cards and neither with
non-removable cards.

Normally, we don't need a connector node, but instead we put the
related properties/phandles in the host controller node. This works
fine!

For SDIO func devices, sometimes we need a child node of the host
controller node, as to be able to describe certain characteristics of
the SDIO func device. So this case is kind of a special type of card
node (because one can have several SDIO func devices attached, even if
this isn't used).

Now, to follow the current bindings, we must not put connector related
bindings in the card node, like the vmmc-supply, perhaps that is what
causes confusion here?

>
>> The mmc pwrseq DT bindings just follows the legacy approach for MMC
>> and that's why the pwrseq handle is at the controller node. Yes, would
>> could have done it differently, but this is the case now, so we will
>> have to accept that.
>
> We're stuck with supporting the existing cases. That doesn't mean
> we're stuck with the same thing for new cases.

Agree!

But I think there is nothing to improve in this case, or am I wrong?

Kind regards
Uffe