linux-kernel - Re: [PATCH] nouveau: pci: quiesce GPU on shutdown

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Message-ID: <CAPM=9txNMnPhaCO9PJb=-kptgWia=18TbfFnQ1W03Cj3dLDCsQ@mail.gmail.com>
Date: Wed, 21 Jan 2026 16:06:00 +1000
From: Dave Airlie <airlied@...il.com>
To: Li Chen <me@...ux.beauty>
Cc: Lyude Paul <lyude@...hat.com>, Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
	Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, 
	Simona Vetter <simona@...ll.ch>, dri-devel <dri-devel@...ts.freedesktop.org>, 
	nouveau <nouveau@...ts.freedesktop.org>, linux-kernel <linux-kernel@...r.kernel.org>, 
	Daniel Palmer <daniel@...f.com>
Subject: Re: [PATCH] nouveau: pci: quiesce GPU on shutdown

On Wed, 21 Jan 2026 at 15:44, Li Chen <me@...ux.beauty> wrote:
>
> Hi Dave,
>
>  > 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().
>
> Dave, if this is ok, I would add it as comment in the next version.

Please do,

Also with that,

Reviewed-by: Dave Airlie <airlied@...hat.com>

>
> Regards,
> Li
>