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SubjectRe: [PATCH] PM / core: Fix supplier device runtime PM usage counter imbalance
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Hi Rafael,

On 2018-06-12 13:00, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
>
> If a device link is added via device_link_add() by the driver of the
> link's consumer device, the supplier's runtime PM usage counter is
> going to be dropped by the pm_runtime_put_suppliers() call in
> driver_probe_device(). However, in that case it is not incremented
> unless the supplier driver is already present and the link is not
> stateless. That leads to a runtime PM usage counter imbalance for
> the supplier device in a few cases.
>
> To prevent that from happening, bump up the supplier runtime
> PM usage counter in device_link_add() for all links with the
> DL_FLAG_PM_RUNTIME flag set that are added at the consumer probe
> time. Use pm_runtime_get_noresume() for that as the callers of
> device_link_add() who want the supplier to be resumed by it should
> pass DL_FLAG_RPM_ACTIVE in flags to it anyway.
>
> Fixes: 21d5c57b3726 (PM / runtime: Use device links)
> Reported-by: Ulf Hansson <ulf.hansson@linaro.org>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> ---
>
> This is a replacement for commit 1e8378619841 (PM / runtime: Fixup
> reference counting of device link suppliers at probe) that is going
> to be reverted.

Thanks Rafael for the patch. I've applied it and now I'm a bit puzzled.
Let's get back to my IOMMU and codec case, mentioned here:
https://marc.info/?l=linux-pm&m=152878741527962&w=2

Now, after applying your patch, when IOMMU creates a link with
DL_FLAG_PM_RUNTIME to the jpeg device (this happens when jpeg device is
being probed), it is not IOMMU is not runtime resumed anymore (that's
because the patch changes pm_runtime_get_sync to pm_runtime_get_noresume).
This means that until jpeg driver enables runtime pm for its device and
finally performs runtime pm suspends/resume cycle, the supplier won't be
resumed. On the other hand, when I add DL_FLAG_RPM_ACTIVE flag to link
creation, the supplier is properly resumed, but then, once the jpeg
device probe finishes, the supplier is still in runtime active state
until a next runtime suspend/resume cycle of jpeg device. If I understand
right, the DL_FLAG_RPM_ACTIVE flag should be there from the beginning,
but that time it runtime pm part of links worked in a bit different way
than now.

Is there any way to keep old behavior?

> ---
> drivers/base/core.c | 15 +++++++--------
> 1 file changed, 7 insertions(+), 8 deletions(-)
>
> Index: linux-pm/drivers/base/core.c
> ===================================================================
> --- linux-pm.orig/drivers/base/core.c
> +++ linux-pm/drivers/base/core.c
> @@ -216,6 +216,13 @@ struct device_link *device_link_add(stru
> link->rpm_active = true;
> }
> pm_runtime_new_link(consumer);
> + /*
> + * If the link is being added by the consumer driver at probe
> + * time, balance the decrementation of the supplier's runtime PM
> + * usage counter after consumer probe in driver_probe_device().
> + */
> + if (consumer->links.status == DL_DEV_PROBING)
> + pm_runtime_get_noresume(supplier);
> }
> get_device(supplier);
> link->supplier = supplier;
> @@ -234,14 +241,6 @@ struct device_link *device_link_add(stru
> case DL_DEV_DRIVER_BOUND:
> switch (consumer->links.status) {
> case DL_DEV_PROBING:
> - /*
> - * Balance the decrementation of the supplier's
> - * runtime PM usage counter after consumer probe
> - * in driver_probe_device().
> - */
> - if (flags & DL_FLAG_PM_RUNTIME)
> - pm_runtime_get_sync(supplier);
> -
> link->status = DL_STATE_CONSUMER_PROBE;
> break;
> case DL_DEV_DRIVER_BOUND:
>
>
>
>

Best regards
--
Marek Szyprowski, PhD
Samsung R&D Institute Poland

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