Nouveau - Nov 2017 - [PATCH] pci: do a msi rearm on init

On my GP107 when I load nouveau after unloading it, for some reason the
GPU stopped sending or the CPU stopped receiving interrupts if MSI was
enabled.

Doing a rearm once before getting any interrupts fixes this.

Signed-off-by: Karol Herbst <kherbst at redhat.com>
---
 drm/nouveau/nvkm/subdev/pci/base.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drm/nouveau/nvkm/subdev/pci/base.c
b/drm/nouveau/nvkm/subdev/pci/base.c
index b1b1f362..7ee1fbb4 100644
--- a/drm/nouveau/nvkm/subdev/pci/base.c
+++ b/drm/nouveau/nvkm/subdev/pci/base.c
@@ -136,6 +136,10 @@ nvkm_pci_init(struct nvkm_subdev *subdev)
 		return ret;
 
 	pci->irq = pdev->irq;
+	/* workaround: do a rearm once */
+	if (pci->msi)
+		pci->func->msi_rearm(pci);
+
 	return ret;
 }
 
-- 
2.14.3

On Fri, Nov 24, 2017 at 03:56:26AM +0100, Karol Herbst
wrote:
> On my GP107 when I load nouveau after unloading it, for some reason the
> GPU stopped sending or the CPU stopped receiving interrupts if MSI was
> enabled.
I suppose this could happen if the GPU raises an interrupt after the
driver's already called free_irq() on it, and hence the driver can't
rearm itself in the interrupt handler.

This possibly points to a bug somewhere (the GPU should be completely
idle by the time free_irq() is called), but this seems like a valid
thing to do at initialization in any case to avoid relying on the prior
owner of the device to always behave properly.
> Doing a rearm once before getting any interrupts fixes this.
> 
> Signed-off-by: Karol Herbst <kherbst at redhat.com>
> ---
>  drm/nouveau/nvkm/subdev/pci/base.c | 4 ++++
>  1 file changed, 4 insertions(+)
Reviewed-by: Thierry Reding <treding at nvidia.com>
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On Fri, Nov 24, 2017 at 3:02 PM, Thierry Reding
<thierry.reding at gmail.com> wrote:
> On Fri, Nov 24, 2017 at 03:56:26AM +0100, Karol Herbst wrote:
>> On my GP107 when I load nouveau after unloading it, for some reason the
>> GPU stopped sending or the CPU stopped receiving interrupts if MSI was
>> enabled.
>
> I suppose this could happen if the GPU raises an interrupt after the
> driver's already called free_irq() on it, and hence the driver
can't
> rearm itself in the interrupt handler.
>
> This possibly points to a bug somewhere (the GPU should be completely
> idle by the time free_irq() is called), but this seems like a valid
> thing to do at initialization in any case to avoid relying on the prior
> owner of the device to always behave properly.
>
Yeah, this makes sense. But what I am wondering about is, why this
isn't a bigger problem or maybe this is just due to those changes in
the Pascal interrupt handler and this is a Pascal only problem?
Anyway, the Nvidia driver seems to do it once on loading time as well,
so I was quite sure we could simply do it this way and be sure that we
are able to use the GPU from any state.
>> Doing a rearm once before getting any interrupts fixes this.
>>
>> Signed-off-by: Karol Herbst <kherbst at redhat.com>
>> ---
>>  drm/nouveau/nvkm/subdev/pci/base.c | 4 ++++
>>  1 file changed, 4 insertions(+)
>
> Reviewed-by: Thierry Reding <treding at nvidia.com>