Re: [PATCH] nouveau: pci: quiesce GPU on shutdown

[Li Chen <me@linux.beauty>]

Hi Danilo

 > On Wed Jan 21, 2026 at 1:50 AM CET, Li Chen wrote:
 > >  > > +       usleep_range(200, 400);\
 > >  > 
 > >  > Why is this needed? it at least needs a comment.
 > >
 > > This patch is needed for kexec/KHO/LUO reboot: firmware reset is skipped, so the GPU may remain in an active/DMA 
 > > state and the next kernel can fail to re-init nouveau. We can’t call the full DRM/TTM teardown from ->shutdown() because
 > > userspace may still hold DRM fds during shutdown, which triggers WARNs.
 > >
 > > So the shutdown hook reuses the suspend/quiesce path (safe with open fds) and then powers down the PCI function (D3hot)
 > > to leave the device in a consistent state for the next kernel.
 > 
 > I think the question was about the usleep_range() specifically. :)
 >

Thanks for the hint. 

That usleep_range(200, 400) is just to give the PCI power transition time to settle before an immediate kexec jump.

 It’s mirroring the existing nouveau_pmops_suspend() behavior, which already does udelay(200) right after pci_set_power_state(..., PCI_D3hot). In ->shutdown() we’re allowed to
 sleep, so I used usleep_range() instead of a busy-wait udelay().
 
Regards,
Li​