On Mon, Dec 16, 2024 at 5:23 PM Christoph Hellwig <hch@xxxxxx> wrote: > > On Sat, Dec 14, 2024 at 12:00:23PM +0530, Manivannan Sadhasivam wrote: > > We need a PM core API that tells the device drivers when it is safe to powerdown > > the devices. The usecase here is with PCIe based NVMe devices but the problem is > > applicable to other devices as well. > > Maybe I'm misunderstanding things, but I think the important part is > to indicate when a suspend actually MUST put the device into D3. Because > doing that should always be safe, but not always optimal. I'm not aware of any cases when a device must be put into D3cold (which I think is what you mean) during system-wide suspend. Suspend-to-idle on x86 doesn't require this, at least not for correctness. I don't think any platforms using DT require it either. In theory, ACPI S3 or hibernation may request that, but I've never seen it happen in practice. Suspend-to-idle on x86 may want devices to end up in specific power states in order to be able to switch the entire platform into a deep energy-saving mode, but that's never been D3cold so far.
