On Thu, Feb 15, 2024 at 07:39:08PM +0530, Manivannan Sadhasivam wrote: > On Wed, Feb 14, 2024 at 04:02:28PM -0600, Bjorn Helgaas wrote: > > On Tue, Feb 06, 2024 at 10:40:43PM +0530, Manivannan Sadhasivam wrote: > > > ... > > > > > ... And for your usecase, allowing the controller driver to > > > start the link post boot just because a device on your Pixel > > > phone comes up later is not a good argument. You _should_not_ > > > define the behavior of a controller driver based on one > > > platform, it is really a bad design. > > > > I haven't followed the entire discussion, and I don't know much > > about the specifics of Ajay's situation, but from the controller > > driver's point of view, shouldn't a device coming up later look > > like a normal hot-add? > > Yes, but most of the form factors that these drivers work with do > not support native hotplug. So users have to rescan the bus through > sysfs. > > > I think most drivers are designed with the assumption that > > Endpoints are present and powered up at the time of host > > controller probe, which seems a little stronger than necessary. > > Most of the drivers work with endpoints that are fixed in the board > design (like M.2), so the endpoints would be up when the controller > probes. > > > I think the host controller probe should initialize the Root Port > > such that its LTSSM enters the Detect state, and that much should > > be basically straight-line code with no waiting. If no Endpoint > > is attached, i.e., "the slot is empty", it would be nice if the > > probe could then complete immediately without waiting at all. > > Atleast on Qcom platforms, the LTSSM would be in "Detect" state even > if no endpoints are found during probe. Then once an endpoint comes > up later, link training happens and user can rescan the bus through > sysfs. Can the hardware tell us when the link state changes? If so, we should be able to scan the bus automatically without the need for sysfs. For example, if the Root Port advertised PCI_EXP_FLAGS_SLOT, we might be able to use a Data Link Layer State Changed interrupt to scan the bus via pciehp when the Endpoint is powered up, even if the Endpoint is actually soldered down and not physically hot-pluggable. Bjorn
