On 13/08/2019 10:30, Chunfeng Yun wrote: > On Mon, 2019-08-12 at 16:04 +0300, Roger Quadros wrote: >> >> On 12/08/2019 15:46, Felipe Balbi wrote: >>> >>> Hi, >>> >>> Roger Quadros <rogerq@xxxxxx> writes: >>>>> The sysfs file we expose from the class for the role switches is >>>>> primarily meant for supporting proprietary protocols that require us >>>>> to basically override the connector USB data role. The default role >>>>> should always be selected in the drivers. >>>> >>>> OK. Let's take this example >>>> - Port is dual-role port micro AB. >>>> - microAB to type-A adapter is connected which pulls ID low. port transitions >>>> to "host" role by the controller driver. >>>> - proprietary protocol want to switch role to device role so writes "device" to >>>> mode switch sysfs. port transitions to "device" role. >>>> >>>> Now, how does controller driver know to fall back to HW based role switching? >>> >>> Use a 'disconnect' or 'suspend' event to go reset it? But that should, >>> probably, be done at kernel space, no? >>> >> >> Yes that could be one option. >> So after a disconnect, sysfs role should reflect actual hardware role. correct? > > Maybe it's difficult to support both HW based role switch and SW based > role switch by sysfs at the same if the HW's FSM rely on, such as, the > state of Vbus pin or ID pin. Likes the upper example, when user writes > "device" to mode switch sysfs, the driver should skip the HW state of ID > pin, due to it's state is Low, or force it as High. > We do need a clear way of indicating that SW wants to override so HW state is ignored. > Another option way is that introduces a property in DTS to indicate the > way the driver want to use (HW based or SW based, usb_role_switch > doesn't provide this information for the controller driver), but is not > flexible enough. That is not good enough for us. We need both HW and SW based role switching. Can we introduce a new state (e.g. "auto") in usb_role_switch. This would explicitly indicate the driver to do HW based switching. This way we don't need to depend on connect/disconnect events and can do role switch tests even without cable/device connected. -- cheers, -roger Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki. Y-tunnus/Business ID: 0615521-4. Kotipaikka/Domicile: Helsinki
