[+cc Sinan, Lukas] Hi Daniel, On Mon, Nov 14, 2016 at 07:40:03PM +0100, Daniel Vetter wrote: > On Fri, Nov 11, 2016 at 02:37:23PM +0000, Emil Velikov wrote: > > From: Emil Velikov <emil.velikov@xxxxxxxxxxxxx> > > > > Currently the revision isn't available via sysfs/libudev thus if one > > wants to know the value they need to read through the config file. > > > > This in itself wakes/powers up the device, causing unwanted delay > > since it can be quite costly. > > > > There are at least two userspace components which could make use the new > > file libpciaccess and libdrm. The former [used in various places] wakes > > up _every_ PCI device, which can be observed via glxinfo [when using > > Mesa 10.0+ drivers]. While the latter [in association with Mesa 13.0] > > can lead to 2-3 second delays while starting firefox, thunderbird or > > chromium. > > > > Expose the revision as a separate file, just like we do for the device, > > vendor, their subsystem version and class. > > > > Cc: Bjorn Helgaas <bhelgaas@xxxxxxxxxx> > > Cc: linux-pci@xxxxxxxxxxxxxxx > > Cc: Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> > > Link: https://bugs.freedesktop.org/show_bug.cgi?id=98502 > > Tested-by: Mauro Santos <registo.mailling@xxxxxxxxx> > > Reviewed-by: Alex Deucher <alexander.deucher@xxxxxxx> > > Signed-off-by: Emil Velikov <emil.velikov@xxxxxxxxxxxxx> > > Given that waking a gpu can take somewhere between ages and forever, and > that we read the pci revisions everytime we launch a new gl app I think > this is the correct approach. Of course we could just patch libdrm and > everyone to not look at the pci revision, but that just leads to every > pci-based driver having a driver-private ioctl/getparam thing to expose > it. Which also doesn't make much sense. This re-asserts what has already been said, but doesn't address any of my questions in the v2 discussion, so I'm still looking to continue that thread. I am curious about this long wakeup issue, though. Are we talking about a D3cold -> D0 transition? I assume so, since config space is generally accessible in all power states except D3cold. From the device's point of view this is basically like a power-on. I think the gist of PCIe r3.0, sec 6.6.1 is that we need to wait 100ms, e.g., PCI_PM_D3COLD_WAIT, before doing config accesses. We do support Configuration Request Retry Status Software Visibility (pci_enable_crs()), so a device *can* take longer than 100ms after power-up to respond to a config read, but I think that only applies to reads of the Vendor ID. I cc'd Sinan because we do have some issues with our CRS support, and maybe he can shed some light on this. I'm not surprised if a GPU takes longer than 100ms to do device- specific, driver-managed, non-PCI things like detect and wake up monitors. But I *am* surprised if generic PCI bus-level things like config reads take longer than that. I also cc'd Lukas because he knows a lot more about PCI PM than I do. Bjorn -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
