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. 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
