Message-ID: <CAGb2v6783ERJHPd5ov3Ebf+V5LNm+bL=ypAgetPLigSyW6_niQ@mail.gmail.com>
Date:   Tue, 1 May 2018 23:52:11 +0800
From:   Chen-Yu Tsai <wens@...e.org>
To:     André Przywara <andre.przywara@....com>
Cc:     Icenowy Zheng <icenowy@...c.io>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Maxime Ripard <maxime.ripard@...tlin.com>,
        linux-mmc@...r.kernel.org, devicetree <devicetree@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-sunxi <linux-sunxi@...glegroups.com>
Subject: Re: [linux-sunxi] [PATCH 3/3] arm64: allwinner: h6: enable MMC0/2 on
 Pine H64

On Mon, Apr 30, 2018 at 6:44 PM, Andre Przywara <andre.przywara@....com> wrote:
> Hi,
>
> On 30/04/18 10:51, Icenowy Zheng wrote:
>>
>>
>> 于 2018年4月30日 GMT+08:00 下午5:47:35, Andre Przywara <andre.przywara@....com> 写到:
>>> Hi Icenowy,
>>>
>>> On 27/04/18 08:12, Icenowy Zheng wrote:
>>>>
>>>>
>>>> 于 2018年4月27日 GMT+08:00 上午12:46:26, Andre Przywara
>>> <andre.przywara@....com> 写到:
>>>>> Hi,
>>>>>
>>>>> On 26/04/18 15:07, Icenowy Zheng wrote:
>>>>>> The Pine H64 board have a MicroSD slot connected to MMC0 controller
>>>>> of
>>>>>> the H6 SoC and a eMMC slot connected to MMC2.
>>>>>>
>>>>>> Enable them in the device tree.
>>>>>>
>>>>>> Signed-off-by: Icenowy Zheng <icenowy@...c.io>
>>>>>> ---
>>>>>>  .../boot/dts/allwinner/sun50i-h6-pine-h64.dts      | 32
>>>>> ++++++++++++++++++++++
>>>>>>  1 file changed, 32 insertions(+)
>>>>>>
>>>>>> diff --git a/arch/arm64/boot/dts/allwinner/sun50i-h6-pine-h64.dts
>>>>> b/arch/arm64/boot/dts/allwinner/sun50i-h6-pine-h64.dts
>>>>>> index d36de5eb81f3..78b1cd54687c 100644
>>>>>> --- a/arch/arm64/boot/dts/allwinner/sun50i-h6-pine-h64.dts
>>>>>> +++ b/arch/arm64/boot/dts/allwinner/sun50i-h6-pine-h64.dts
>>>>>> @@ -20,6 +20,38 @@
>>>>>>   chosen {
>>>>>>           stdout-path = "serial0:115200n8";
>>>>>>   };
>>>>>> +
>>>>>> + reg_vcc3v3: vcc3v3 {
>>>>>> +         compatible = "regulator-fixed";
>>>>>> +         regulator-name = "vcc3v3";
>>>>>> +         regulator-min-microvolt = <3300000>;
>>>>>> +         regulator-max-microvolt = <3300000>;
>>>>>> + };
>>>>>> +
>>>>>> + reg_vcc1v8: vcc1v8 {
>>>>>> +         compatible = "regulator-fixed";
>>>>>> +         regulator-name = "vcc1v8";
>>>>>> +         regulator-min-microvolt = <1800000>;
>>>>>> +         regulator-max-microvolt = <1800000>;
>>>>>> + };
>>>>>> +};
>>>>>> +
>>>>>> +&mmc0 {
>>>>>> + pinctrl-names = "default";
>>>>>> + pinctrl-0 = <&mmc0_pins>;
>>>>>> + vmmc-supply = <&reg_vcc3v3>;
>>>>>
>>>>> So this is actually CLDO1 on the AXP, correct?
>>>>
>>>> I remember it's coupled between two LDOs, to provide enough power.
>>>>
>>>>>
>>>>>
>>>>>> + cd-gpios = <&pio 5 6 GPIO_ACTIVE_LOW>;
>>>>>> + status = "okay";
>>>>>> +};
>>>>>> +
>>>>>> +&mmc2 {
>>>>>> + pinctrl-names = "default";
>>>>>> + pinctrl-0 = <&mmc2_pins>;
>>>>>> + vmmc-supply = <&reg_vcc3v3>;
>>>>>> + vqmmc-supply = <&reg_vcc1v8>;
>>>>>
>>>>> And this is BLDO2?
>>>>
>>>> Yes.
>>>>
>>>>>
>>>>> I am just asking because I want to avoid running into the same
>>> problem
>>>>> as with the A64 before: that future DTs become incompatible with
>>> older
>>>>> kernels, because we change the power supply to point to the AXP
>>>>> regulators, which this kernel does not support yet.
>>>>
>>>> The answer is just not to keep this compatibility, as it's not
>>>> supported option to update DT without updating kernel.
>>>
>>> Well, I recognise that statement.. ;-) and I understand that it's far
>>> easier to handle it this way. But:
>>> - Which .dtb are we going to write into the SPI flash? An older one,
>>> which covers all kernels, but lacks features? Or a newer one, which
>>> limits the bootable kernels to recent versions?
>>> - Which DT are we going to give to EFI applications?
>>> - Which DT are the BSDs suspected to take? They don't ship their own
>>> DTs
>>> (which is good!).
>>>
>>> So I understand that "shipping the DT with the kernel" is the old
>>> (embedded!) way of doing things, but I really believe we should stop
>>> relying on this and try to come up with backwards compatible DTs, which
>>> live in the firmware and get updated there. Because this is what the
>>> distros seem to expect from ARM64 boards these days.
>>
>> I think in this way we should change the way to submit
>> patches -- let DT binding patch be merged when it's ready,
>> and do not wait for driver.
>
> Yes, I agree. Ideally we would look at the hardware description, create
> a binding just based on that and submit it.
>
> Then the actual DTs and the drivers (for Linux, U-Boot, *BSD,
> you-name-it) could be done independently from each other.
>
> I think we should really aim for that. The only question is whether this
> is really practical, since the documentation is sometimes lacking and we
> may discover missing properties during driver development.
> So when we meanwhile do hand-in-hand development, we should make sure we
> don't break anything in the future.

We could do that, but for critical regulators it's a bit tricky. Like the
issue with vmmc and vqmmc, where the driver for the regulator is missing,
leading to an unusable system.

>>>> P.S. I think the DT will update twice on the kernel side, the
>>>> first time keep reg_vcc3v3 (as it's coupled) but use real
>>>> regulator for reg_vcc1v8, the second time use the real
>>>> coupled regulator for reg_vcc3v3.
>>>>
>>>>>
>>>>> It looks like there are more users of those power rails, so we could
>>>>> keep those supplies connected to these fixed regulators here, even
>>> with
>>>>> AXP-805 support in the kernel.
>>>>
>>>> It's not a good choice.
>>>>
>>>>>
>>>>> Or we keep this back until we get proper AXP support in the kernel?
>>> I
>>>>> guess it's quite close to the existing PMICs, so it might be more a
>>>>> copy&paste exercise to support the AXP-805?
>>>>
>>>> It's not a reason to keep it back.
>>>
>>> So I compared the manuals of the AXP806 and the AXP805, the register
>>> interface looks identical to me. I only have a (somewhat) Chinese
>>> version of the AXP806 manual, so couldn't really find the difference
>>> between the two. Do you know more about it? Is it just maybe the
>>> packaging and the electrical properties (like max current supported)?
>>>
>>> If the I2C register interface is really the same, we could just add the
>>> DT nodes for the regulator and be done.
>>
>> They're the same. My following patchset adds AXP805
>> compatible just to use AXP806 code. I have asked Wink
>> and the answer is that they have only preset difference.
>
> Ah, thanks for that, that's good info!
> So in this case we don't even need to add the compatible name to the
> driver, just add it to the binding doc and create (or copy) the DT
> snippets. See last week's discussion ;-)

We need to add the compatible to the I2C side of the AXP driver. Also
the property for "standalone mode". I believe I already touched on this
before in another discussion with Icenowy.

> And we could aim to merge this together with the MMC driver, so that
> there would be no regression.
> Isn't that doable? I am happy to review patches on short notice (if you
> have them already, otherwise I am happy to make them).
>
> So in summary it looks like all changes could be purely binding doc/DT
> changes, so any 4.17 kernel would work already, when presented with the
> right DT.

No it won't. See above about the I2C driver.

ChenYu

>
> Cheers,
> Andre.
>
>
>>
>>>
>>> Cheers,
>>> Andre.
>>>
>>>>
>>>>>
>>>>> But apart from this this looks correct to me.
>>>>>
>>>>> Cheers,
>>>>> Andre.
>>>>>
>>>>>> + non-removable;
>>>>>> + cap-mmc-hw-reset;
>>>>>> + status = "okay";
>>>>>>  };
>>>>>>
>>>>>>  &uart0 {
>>>>>>
>
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