linux-kernel - Re: [PATCH v3] usb: dwc3: Add support for VBUS power control

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Message-ID: <78282590-5190-300c-4d17-3ce9cd63acac@topic.nl>
Date:   Mon, 7 Sep 2020 09:50:52 +0200
From:   Mike Looijmans <mike.looijmans@...ic.nl>
To:     Felipe Balbi <balbi@...nel.org>, Mark Brown <broonie@...nel.org>
CC:     Vincent Whitchurch <vincent.whitchurch@...s.com>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        gregkh@...uxfoundation.org, lgirdwood@...il.com
Subject: Re: [PATCH v3] usb: dwc3: Add support for VBUS power control


Met vriendelijke groet / kind regards,

Mike Looijmans
System Expert


TOPIC Embedded Products B.V.
Materiaalweg 4, 5681 RJ Best
The Netherlands

T: +31 (0) 499 33 69 69
E: mike.looijmans@...icproducts.com
W: www.topicproducts.com

Please consider the environment before printing this e-mail
On 07-09-2020 09:44, Felipe Balbi wrote:
> Hi,
>
> Mike Looijmans <mike.looijmans@...ic.nl> writes:
>> Met vriendelijke groet / kind regards,
>>
>> Mike Looijmans
>> System Expert
>>
>>
>> TOPIC Embedded Products B.V.
>> Materiaalweg 4, 5681 RJ Best
>> The Netherlands
>>
>> T: +31 (0) 499 33 69 69
>> E: mike.looijmans@...icproducts.com
>> W: www.topicproducts.com
>>
>> Please consider the environment before printing this e-mail
>> On 27-07-2020 12:23, Mark Brown wrote:
>>> On Sun, Jul 26, 2020 at 09:10:39AM +0200, Mike Looijmans wrote:
>>>> On 23-07-2020 13:05, Mark Brown wrote:
>>>>> Does the device actually support running without power so that's a thing
>>>>> that can happen?  _get_optional() should only ever be used for supplies
>>>>> that may be physically absent.
>>>> It's the 5V VBUS power for the USB "plug" that's being controlled here. It
>>>> must turned on when the controller is in "host" mode. Some boards arrange
>>>> this in hardware through the PHY, and some just don't have any control at
>>>> all and have it permanently on or off. On a board where the 5V is controlled
>>>> using a GPIO line or an I2C chip, this patch is required to make it work.
>>> That sounds like the driver should not be using _get_optional() then.
>>>
>> Making it mandatory would break most (read: all except Topic's) existing
>> boards as they won't have it in their devicetree. I'm perfectly okay with
>> that, but others might disagree.
> you're perfectly okay with break all existing users of the driver?
> That's a bit harsh
>
It turned out that "optional" when used for regulators means the 
opposite of when used in clk context. For regulators, "optional" means 
"don't supply a dummy regulator if there's none provided". So 
get_optional will just fail when the supply isn't defined, while 
get_regulator will just return a dummy in that case.

So the v4 patch which doesn't use "_get_optional" works for both cases 
and doesn't break existing use(r)s.

-- 
Mike Looijmans