linux-kernel - Re: [PATCH v3 2/2] usb: gadget: composite: Draw 100mA current if not configured

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Message-ID: <20230227193840.mygvoxz7soklf4vm@synopsys.com>
Date:   Mon, 27 Feb 2023 19:38:43 +0000
From:   Thinh Nguyen <Thinh.Nguyen@...opsys.com>
To:     Prashanth K <quic_prashk@...cinc.com>
CC:     Thinh Nguyen <Thinh.Nguyen@...opsys.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jakob Koschel <jakobkoschel@...il.com>,
        Jó Ágila Bitsch <jgilab@...il.com>,
        Alan Stern <stern@...land.harvard.edu>,
        Pratham Pratap <quic_ppratap@...cinc.com>,
        Jack Pham <quic_jackp@...cinc.com>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 2/2] usb: gadget: composite: Draw 100mA current if not
 configured

On Sat, Feb 25, 2023, Prashanth K wrote:
> 
> 
> On 25-02-23 12:08 am, Thinh Nguyen wrote:
> > On Fri, Feb 24, 2023, Prashanth K wrote:
> > > 
> > > 
> > > On 24-02-23 01:40 am, Thinh Nguyen wrote:
> > > > On Thu, Feb 23, 2023, Prashanth K wrote:
> > > > > Currently we don't change the current value if device isn't in
> > > > > configured state. But the battery charging specification says,
> > > > 
> > > > Can you provide the spec section also?
> > > > 
> > > 1.2 Background
> > > 1.4.13 Standard Downstream Port
> > > 
> > > Did you mean to add these in the commit message?
> > 
> > Yes, it's better to have the reference in case we need to revisit this.
> I have added it in v4 patch, thanks for pointing it out.
> > 
> > > > > device can draw up to 100mA of current if its in unconfigured
> > > > 
> > > > Is this related to being self-powered?
> > 
> > > I think its applicable for bus-powered devices.
> > 
> > No, I mean before configured state, is the device considered
> > self-powered? Since being self-powered means drawing 100mA or less, we
> > can use USB_SELF_POWER_VBUS_MAX_DRAW to provide more context. If it's
> > totally unrelated, then you can ignore this.
> > 
> > Thanks,
> > Thinh
> As per my understanding, those are 2 different things. A self-powered device
> isn't allowed to draw more than 100mA. And an unconfigured device
> isn't allowed to draw more than 100mA (in HS). One thing that I recently
> found out is that, as per usb3.0 spec, SS device can only draw up to 150mA
> if its unconfigured state. So i have to check the speed and set the current
> values accordingly.

I see. Thanks for the info.

Thanks,
Thinh