From: Felipe Balbi <balbi@kernel.org>
To: Jack Pham <jackp@codeaurora.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: linux-usb@vger.kernel.org, Jack Pham <jackp@codeaurora.org>,
Ronak Vijay Raheja <rraheja@codeaurora.org>
Subject: Re: [PATCH] usb: gadget: composite: Allow bMaxPower=0 if self-powered
Date: Tue, 20 Jul 2021 12:31:56 +0300 [thread overview]
Message-ID: <87y2a1xreb.fsf@kernel.org> (raw)
In-Reply-To: <20210720080907.30292-1-jackp@codeaurora.org>
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Jack Pham <jackp@codeaurora.org> writes:
> Currently the composite driver encodes the MaxPower field of
> the configuration descriptor by reading the c->MaxPower of the
> usb_configuration only if it is non-zero, otherwise it falls back
> to using the value hard-coded in CONFIG_USB_GADGET_VBUS_DRAW.
> However, there are cases when a configuration must explicitly set
> bMaxPower to 0, particularly if its bmAttributes also has the
> Self-Powered bit set, which is a valid combination.
>
> This is specifically called out in the USB PD specification section
> 9.1, in which a PDUSB device "shall report zero in the bMaxPower
> field after negotiating a mutually agreeable Contract", and also
> verified by the USB Type-C Functional Test TD.4.10.2 Sink Power
> Precedence Test.
>
> The fix allows the c->MaxPower to be used for encoding the bMaxPower
> even if it is 0, if the self-powered bit is also set. An example
> usage of this would be for a ConfigFS gadget to be dynamically
> updated by userspace when the Type-C connection is determined to be
> operating in Power Delivery mode.
>
> Co-developed-by: Ronak Vijay Raheja <rraheja@codeaurora.org>
> Signed-off-by: Ronak Vijay Raheja <rraheja@codeaurora.org>
> Signed-off-by: Jack Pham <jackp@codeaurora.org>
Nice catch!
Acked-by: Felipe Balbi <balbi@kernel.org>
--
balbi
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prev parent reply other threads:[~2021-07-20 9:32 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-20 8:09 [PATCH] usb: gadget: composite: Allow bMaxPower=0 if self-powered Jack Pham
2021-07-20 9:31 ` Felipe Balbi [this message]
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