On Tue, 2019-08-13 at 10:48 +0300, Roger Quadros wrote: > > 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. But "auto" is not a role? How about introducing a new attribute in usb_role_switch? > > This way we don't need to depend on connect/disconnect events and can > do role switch tests even without cable/device connected. >
