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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <be4013b6-01c6-7f67-35ad-5c398b85c066@topic.nl>
Date:   Mon, 27 Jul 2020 13:50:26 +0200
From:   Mike Looijmans <mike.looijmans@...ic.nl>
To:     Mark Brown <broonie@...nel.org>
CC:     Vincent Whitchurch <vincent.whitchurch@...s.com>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        balbi@...nel.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 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.