On 21-01-25 08:36 pm, Alan Stern wrote: > On Tue, Jan 21, 2025 at 09:50:08AM +0530, Prashanth K wrote: >> >> >> On 20-01-25 08:17 pm, Alan Stern wrote: >>> 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 >>> >> >> Right, set_config() in composite.c does this in runtime based on the >> values of MaxPower (from configFS), VBUS_DRAW defconfig and speed. >> If we don't set MaxPower from configFS, this config helps to set it >> during compile time. In fact MaxPower in configFS takes its default >> value from CONFIG_USB_GADGET_VBUS_DRAW . Sent this patch because Kconfig >> has this limitation where it's only allowing values upto 500mA. > > Why does MaxPower need to be set at compile time? Why not set it at > runtime instead? > > If MaxPower gets set at runtime then it can take its default value to be > 500 mA or 900 mA depending on the connection speed. There will be no > need for CONFIG_USB_GAGDGET_VBUS_DRAW. > Yes, agreed. Can we mark CONFIG_USB_GAGDGET_VBUS_DRAW as legacy and maybe also avoid configfs/composite from using it? > You are trying to improve a compile-time limitation on a quantity which > isn't known until runtime. The whole idea of doing it that way is > fundamentally wrong. You shouldn't try to improve it a little, you > should fix the basic mistake by doing everything at runtime. > > Alan Stern > Regards, Prashanth K
