On 9/23/2022 8:20 PM, Vivi, Rodrigo wrote:
Rafael, could you please add your thoughts here?
Sure, sorry for the delay.
I gather the idea is to bind the driver to the device without actually
doing anything more to it and to put it into D3, so it doesn't draw too
much power.
Using PM-runtime for that should work, but the driver needs to make sure
that its PM-runtime callbacks will work then (they may simply return 0
all the time in that case, but they need to take it into account).
On Thu, 2022-09-22 at 12:40 +0000, Gupta, Anshuman wrote:
-----Original Message-----
From: Gupta, Anshuman
Sent: Thursday, September 22, 2022 4:40 PM
To: Vivi, Rodrigo <rodrigo.vivi@xxxxxxxxx>; Tvrtko Ursulin
<tvrtko.ursulin@xxxxxxxxxxxxxxx>
Cc: Nikula, Jani <jani.nikula@xxxxxxxxx>; intel-
gfx@xxxxxxxxxxxxxxxxxxxxx; Daniel
J Blueman <daniel@xxxxxxxxx>; Wysocki, Rafael J
<rafael.j.wysocki@xxxxxxxxx>; stable@xxxxxxxxxxxxxxx
Subject: Re: [PATCH] drm/i915: Allow D3 when we are not
actively
managing a known PCI device.
On 9/22/2022 3:13 PM, Rodrigo Vivi wrote:
On Thu, Sep 22, 2022 at 08:56:00AM +0100, Tvrtko Ursulin wrote:
On 21/09/2022 18:39, Rodrigo Vivi wrote:
The force_probe protection actively avoids the probe of i915
to
manage a device that is currently under development. It is a
nice
protection for future users when getting a new platform but
using
some older kernel.
However, when we avoid the probe we don't take back the
registration
of the device. We cannot give up the registration anyway
since we
can have multiple devices present. For instance an integrated
and a
discrete one.
When this scenario occurs, the user will not be able to
change any
of the runtime pm configuration of the unmanaged device. So,
it will
be blocked in D0 state wasting power. This is specially bad
in the
case where we have a discrete platform attached, but the user
is
able to fully use the integrated one for everything else.
So, let's put the protected and unmanaged device in D3. So we
can
save some power.
Reported-by: Daniel J Blueman <daniel@xxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Cc: Daniel J Blueman <daniel@xxxxxxxxx>
Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
Cc: Anshuman Gupta <anshuman.gupta@xxxxxxxxx>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@xxxxxxxxx>
---
drivers/gpu/drm/i915/i915_pci.c | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/drivers/gpu/drm/i915/i915_pci.c
b/drivers/gpu/drm/i915/i915_pci.c index
77e7df21f539..fc3e7c69af2a
100644
--- a/drivers/gpu/drm/i915/i915_pci.c
+++ b/drivers/gpu/drm/i915/i915_pci.c
@@ -25,6 +25,7 @@
#include <drm/drm_color_mgmt.h>
#include <drm/drm_drv.h>
#include <drm/i915_pciids.h>
+#include <linux/pm_runtime.h>
#include "gt/intel_gt_regs.h"
#include "gt/intel_sa_media.h"
@@ -1304,6 +1305,7 @@ static int i915_pci_probe(struct
pci_dev *pdev,
const struct pci_device_id *ent)
{
struct intel_device_info *intel_info =
(struct intel_device_info *) ent-
driver_data;
+ struct device *kdev = &pdev->dev;
int err;
if (intel_info->require_force_probe && @@ -1314,6
+1316,12 @@
static int i915_pci_probe(struct pci_dev *pdev, const struct
pci_device_id
*ent)
"module parameter or
CONFIG_DRM_I915_FORCE_PROBE=%04x configuration option,\n"
"or (recommended) check for kernel
updates.\n",
pdev->device, pdev->device, pdev-
device);
+
+ /* Let's not waste power if we are not
managing the device */
+ pm_runtime_use_autosuspend(kdev);
+ pm_runtime_allow(kdev);
+ pm_runtime_put_autosuspend(kdev);
AFAIK we don't need to enable autosuspend here,
pm_runtime_put_autosuspend() will cause a NULL pointer de-reference
as it will
immediately call the intel_runtime_suspend()(because we haven't
called the
pm_runtime_mark_last_busy) without initializing i915.
I don't see any null pointer dereference here.
The problem is exactly that we do the initialization and the we give up
on the
device and end up blocking the runtime pm in some state that we cannot
change.
Having said that we only need below, in order to let pci core keep
the pci dev in
D3.
pm_runtime_put_noidle()
as for this one here I get:
[ 9036.357078] i915 0000:03:00.0: Runtime PM usage count underflow!
Hi Rodrigo ,
It seems playing with these runtime hooks, will only enable the
"runtime suspend"
but actual state in "PMCSR" pci config is D0 despite device is
runtime suspended, when there is no driver.
Example:
root@DUT2135-DG2MRB:/home/gta# cat
/sys/bus/pci/devices/0000\:03\:00.0/power/runtime_status
suspended
root@DUT2135-DG2MRB:/home/gta# setpci -s 03:00.0 0xd4.l
00000008
(Bits 00:01 are the power state in PMCSR(offset = 4) config register
from PM Cap offset at 0xd0).
Well, this is indeed awkward.
Rafael, do you know what we could be missing here to ensure we get the
proper d3?
I noticed that with the linux param vfio-pci.ids=8086:<dg2_id> it does
get us to the d3.
# setpci -s 03:00.0 0xd4.l
0000010b
While with the approach in this patch or the noidle() I also get
the 00000008
Thanks,
Rodrigo.
Thanks,
Anshuman Gupta.
Br,
Anshuman Gupta
This sequence is black magic to me so can't really comment on
the specifics.
But in general, what I think I've figured out is, that the PCI core
calls our runtime
resume callback before probe:
local_pci_probe:
...
/*
* Unbound PCI devices are always put in D0,
regardless of
* runtime PM status. During probe, the device is set
to
* active and the usage count is incremented. If the
driver
* supports runtime PM, it should call
pm_runtime_put_noidle(),
* or any other runtime PM helper function
decrementing the usage
* count, in its probe routine and
pm_runtime_get_noresume() in
* its remove routine.
*/
pm_runtime_get_sync(dev);
pci_dev->driver = pci_drv;
rc = pci_drv->probe(pci_dev, ddi->id);
if (!rc)
return rc;
if (rc < 0) {
pci_dev->driver = NULL;
pm_runtime_put_sync(dev);
return rc;
}
Yes, in Linux the default is D0 for any unmanaged device. But
then the
user can go there in the sysfs and change the power/control to
'auto'
and get the device to D3.
And if probe fails it calls pm_runtime_put_sync which
presumably does not
provide the symmetry we need?
The main problem I see is that when the probe fail in our case we
don't unregister and i915 is still listed as controlling that
device
as we could see with lspci --nnv.
And any attempt to change the control to 'auto' fails. So we are
forever stuck in D0.
So, I really believe it is better to bring the device to D3 then
leaving it there blocked in D0 forever.
Or forcing users to use another parameter to entirely avoid i915
to
get this device at first place.
Anyway since I can't provide meaningful review I'll copy Imre
since I think he
worked in the area in the past. Just so more eyes is better.
Regards,
Tvrtko
+
return -ENODEV;
}
