linux-kernel - Re: [PATCH] usb: gadget: Increase the limit of USB_GADGET_VBUS

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Message-ID: <894f42a7-50a5-401e-a705-a06eafd6161d@rowland.harvard.edu>
Date: Mon, 20 Jan 2025 09:47:53 -0500
From: Alan Stern <stern@...land.harvard.edu>
To: Prashanth K <prashanth.k@....qualcomm.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Simona Vetter <simona.vetter@...ll.ch>,
	Takashi Iwai <tiwai@...e.de>, linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] usb: gadget: Increase the limit of USB_GADGET_VBUS_DRAW
 to 900mA

On Mon, Jan 20, 2025 at 04:47:02PM +0530, Prashanth K wrote:
> Currently CONFIG_USB_GADGET_VBUS_DRAW limits the maximum current
> drawn from Vbus to be up to 500mA. However USB gadget operating
> in SuperSpeed or higher can draw up to 900mA. Also, MaxPower in
> ConfigFS takes its default value from this config. Hence increase
> the allowed range of CONFIG_USB_GADGET_VBUS_DRAW to 900mA.

Is this the sort of thing that really needs to be a Kconfig option?  Why 
not make the decision at runtime, based on the needs of the gadget or 
function drivers and the connection speed?

Alan Stern

> Signed-off-by: Prashanth K <prashanth.k@....qualcomm.com>
> ---
>  drivers/usb/gadget/Kconfig | 11 +++++++----
>  1 file changed, 7 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/usb/gadget/Kconfig b/drivers/usb/gadget/Kconfig
> index 76521555e3c1..904652c37385 100644
> --- a/drivers/usb/gadget/Kconfig
> +++ b/drivers/usb/gadget/Kconfig
> @@ -97,8 +97,8 @@ config USB_GADGET_DEBUG_FS
>  	   to conserve kernel memory, say "N".
>  
>  config USB_GADGET_VBUS_DRAW
> -	int "Maximum VBUS Power usage (2-500 mA)"
> -	range 2 500
> +	int "Maximum VBUS Power usage (2-900 mA)"
> +	range 2 900
>  	default 2
>  	help
>  	   Some devices need to draw power from USB when they are
> @@ -107,8 +107,11 @@ config USB_GADGET_VBUS_DRAW
>  	   such as an AC adapter or batteries.
>  
>  	   Enter the maximum power your device draws through USB, in
> -	   milliAmperes.  The permitted range of values is 2 - 500 mA;
> -	   0 mA would be legal, but can make some hosts misbehave.
> +	   milliAmperes. The permitted range of values depends on the
> +	   connection speed, for SuperSpeed and higher it's 2 - 900 mA,
> +	   but connections with High-Speed or slower can draw power
> +	   ranging from 2 - 500 mA; 0 mA would be legal, but can make
> +	   some hosts misbehave.
>  
>  	   This value will be used except for system-specific gadget
>  	   drivers that have more specific information.
> -- 
> 2.25.1
> 
>