On Tue, Jan 30, 2024 at 02:30:27PM +0530, Ajay Agarwal wrote: [...] > > > > > > If that's the case with your driver, when are you starting the link training? > > > > > > > > > > > The link training starts later based on a userspace/debugfs trigger. > > > > > > > > > > > > > Why does it happen as such? What's the problem in starting the link during > > > > probe? Keep it in mind that if you rely on the userspace for starting the link > > > > based on a platform (like Android), then if the same SoC or peripheral instance > > > > get reused in other platform (non-android), the it won't be a seamless user > > > > experience. > > > > > > > > If there are any other usecases, please state them. > > > > > > > > - Mani > > > > > > > This SoC is targeted for an android phone usecase and the endpoints > > > being enumerated need to go through an appropriate and device specific > > > power sequence which gets triggered only when the userspace is up. The > > > PCIe probe cannot assume that the EPs have been powered up already and > > > hence the link-up is not attempted. > > > > Still, I do not see the necessity to not call start_link() during probe. If you > I am not adding any logic/condition around calling the start_link() > itself. I am only avoiding the wait for the link to be up if the > controller driver has not defined start_link(). > I'm saying that not defining the start_link() callback itself is wrong. > > add PROBE_PREFER_ASYNCHRONOUS to your controller driver, this delay would become > > negligible. The reason why I'm against not calling start_link() is due to below > > reasons: > > > > 1. If the same SoC gets reused for other platforms, even other android phones > > that powers up the endpoints during boot, then it creates a dependency with > > userspace to always start the link even though the devices were available. > > That's why we should never fix the behavior of the controller drivers based on a > > single platform. > I wonder how the behavior is changing with this patch. Do you have an > example of a platform which does not have start_link() defined but would > like to still wait for a second for the link to come up? > Did you went through my reply completely? I mentioned that the 1s delay would be gone if you add the async flag to your driver and you are ignoring that. But again, I'm saying that not defining start_link() itself is wrong and I've already mentioned the reasons. > For example, consider the intel-gw driver. The 1 sec wait time in its > probe path is also a waste because it explicitly starts link training > later in time. > I previously mentioned that the intel-gw needs fixing since there is no point in starting the link and waiting for it to come up in its probe() if the DWC core is already doing that. - Mani -- மணிவண்ணன் சதாசிவம்
