On Wed, Feb 28, 2024 at 12:10:15AM +0530, Manivannan Sadhasivam wrote: > On Tue, Feb 27, 2024 at 11:37:05AM -0600, Bjorn Helgaas wrote: > > On Tue, Feb 27, 2024 at 10:38:40PM +0530, Manivannan Sadhasivam wrote: > > > On Tue, Feb 27, 2024 at 10:25:35AM -0600, Bjorn Helgaas wrote: > > > > > > [...] > > > > > > > > Ok, I got the issue. TBH, I added the device tree property based on > > > > > the existing quirks for the ACPI devices. But none of the DT based > > > > > platforms I'm aware of (even the legacy Qcom MSM8996 chipset > > > > > released in early 2016) doesn't have any issue with D3hot. But I'm > > > > > just nervous to assume it is the case for all the DT based platforms > > > > > in the wild. > > > > > > > > > > But to proceed further, what is your preference? Should we ammend > > > > > the DT property to make it explicit that the propery only focuses on > > > > > the D3hot capability of the bridge and it works as per the spec > > > > > (PMCSR) or bite the bullet and enable D3hot for all the non-ACPI > > > > > platforms? > > > > > > > > > > We can add quirks for the bridges later on if we happen to receive > > > > > any bug report. > > > > > > > > I would assume all devices support D3hot via PMCSR per spec. We can > > > > add quirks if we discover something that doesn't. > > > > > > When you say "all devices", are you referring to bridges in DT > > > platforms or the bridges across all platforms? > > > > This patch is only concerned with DT, so that's what I'm commenting on > > here. I don't know how to untangle the question of ACPI systems. > > Ok, I just wanted to confirm. > > > This patch affects platform_pci_bridge_d3(), so just based on the > > "platform" in the function name, I would expect it to be concerned > > with the D3cold case and whether the platform supports controlling > > main power. > > > > It looks like this patch says "we can put devices in D3cold if DT has > > 'supports-d3'". But I don't know how to make sense of that because > > that requires (a) platform hardware to control main power and (b) > > software that knows how to use that hardware. Wouldn't this require a > > little more DT description, like "regulator X controls main power for > > this bridge"? And then an OS would only be able to actually use > > D3cold if it knows how to *operate* the regulator, and it doesn't seem > > like DT could answer that. > > Fair point. And for most of the DT based platforms, there is no > dedicated power supply for the bridge described in DT. So > transitioning the bridge to D3cold is not entirely possible in the > OS. > > Since we concluded that enabling D3hot for all bridges in DT > platforms is the way to go, I'll drop supporting the DT property in > next version. > > I'll also remove it from the binding. Sounds good, thanks!
