On Tue, 2016-05-24 at 13:08 +0300, Heikki Krogerus wrote: > Hi Guenter, > > On Mon, May 23, 2016 at 09:52:12AM -0700, Guenter Roeck wrote: > > On Mon, May 23, 2016 at 05:55:04PM +0200, Oliver Neukum wrote: > > > On Mon, 2016-05-23 at 07:43 -0700, Guenter Roeck wrote: > > > > On 05/23/2016 06:58 AM, Oliver Neukum wrote: > > > > > > > > Now I am confused. Are you saying that the choice of Alternate Mode does > > > > > not belong into user space? > > > > > > > > > > > > > No; sorry for the confusion. The above was meant to apply to my use > > > > of "preferred mode", not yours. I was trying to say that the choice of > > > > preferred roles (which determines if Try.SRC or Try.SNK is enabled) > > > > should belong primarily into the kernel, to be determined by the platform > > > > (presumably via ACPI, devicetree data, or platform data). If it should > > > > > > Why on earth? That is most clearly a policy decision. > > > > > > > The question is not that much if it is policy (it is), but if the policy > > should be driven by the platform or by user space. I think there needs > > to be at least a default driven by the platform. As already mentioned, > > I am ok with a means to override this platform default from user space. > > But if user space doesn't say, there still needs to be a default. > > I don't completely agree with that. The platform should not, and > actually in most cases with ACPI AFAIK, will not provide any > "preferences" to the OS about anything. The platform should only > provide the OS the physical capabilities and nothing else. So if for > example the platform is capable of acting as only source with a Type-C > port, that is what it needs to tell to the OS so possibly the PHY can > be programmed accordingly, etc. May I suggest that the point is moot as long as we agree that user space needs to be able to set a policy? The OS cannot ignore the port before user space tells it what to do. So a default will be needed. The OS must act conservatively, which means it cannot deactivate hardware. So if a port can do DRP, that must be the default. I would go so far that I would suggest that we add a module parameter for Try.SRC and Try.SNK to avoid trouble during boot. > So IMO, just like with any decision related to what the system will > ultimately be used for, decision about the preferred role really > belongs to the userspace. Yes, but ought the APIs for role, mode and PD be separate or not. Sorry to sound like a broken record, but you need to provide some higher level planning here. Regards Oliver -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
