Re: Time to re-enable Runtime PM per default for PCI devcies?

Heiner Kallweit
2020-12-31T09:54:05Z

On 31.12.2020 10:38, Heiner Kallweit wrote:
> On 31.12.2020 05:07, Lukas Wunner wrote:
>> On Wed, Dec 30, 2020 at 11:56:04PM +0100, Heiner Kallweit wrote:
>>> --- a/drivers/pci/pci.c
>>> +++ b/drivers/pci/pci.c
>>> @@ -3024,7 +3024,9 @@ void pci_pm_init(struct pci_dev *dev)
>>> u16 status;
>>> u16 pmc;
>>>
>>> - pm_runtime_forbid(&dev->dev);
>>> + if (pci_acpi_forbid_runtime_pm())
>>> + pm_runtime_forbid(&dev->dev);
>>> +
>>
>> Generic PCI code usually does not call ACPI-specific functions directly,
>> but rather through a pci_platform_pm_ops callback.
>>
>> FWIW, if platform_pci_power_manageable() returns true, it can probably
>> be assumed that allowing runtime PM by default is okay. So as a first
>> step, you may want to call that instead of adding a new callback.
>>
> I don't think that's sufficient. Most likely all the broken old systems
> return true for platform_pci_power_manageable(). So yes, most likely
> we'd need a new callback if we want to have the platform ops abstraction.
> But it could be an optional callback, something like: forbid_runtime_pm
> The question is just: is it worth it?
>
> By the way: pci_set_platform_pm() returns an error if a callback isn't
> set, but no existing caller bothers to check the return code.
>
>> Thanks,
>>
>> Lukas
>>
> Heiner
>

This would be the version with the abstraction.

---
drivers/pci/pci-acpi.c | 6 ++++++
drivers/pci/pci.c | 9 ++++++++-
drivers/pci/pci.h | 5 ++++-
3 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/drivers/pci/pci-acpi.c b/drivers/pci/pci-acpi.c
index 53502a751..b57a79af7 100644
--- a/drivers/pci/pci-acpi.c
+++ b/drivers/pci/pci-acpi.c
@@ -1108,6 +1108,11 @@ static bool acpi_pci_need_resume(struct pci_dev *dev)
return !!adev->power.flags.dsw_present;
}

+static bool acpi_pci_forbid_runtime_pm(void)
+{
+ return acpi_gbl_FADT.header.revision < 6;
+}
+
static const struct pci_platform_pm_ops acpi_pci_platform_pm = {
.bridge_d3 = acpi_pci_bridge_d3,
.is_manageable = acpi_pci_power_manageable,
@@ -1117,6 +1122,7 @@ static const struct pci_platform_pm_ops acpi_pci_platform_pm = {
.choose_state = acpi_pci_choose_state,
.set_wakeup = acpi_pci_wakeup,
.need_resume = acpi_pci_need_resume,
+ .forbid_runtime_pm = acpi_pci_forbid_runtime_pm,
};

void acpi_pci_add_bus(struct pci_bus *bus)
diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index b9fecc25d..3af832b7f 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -982,6 +982,12 @@ static inline bool platform_pci_need_resume(struct pci_dev *dev)
return pci_platform_pm ? pci_platform_pm->need_resume(dev) : false;
}

+static inline bool platform_pci_forbid_runtime_pm(void)
+{
+ return pci_platform_pm && pci_platform_pm->forbid_runtime_pm ?
+ pci_platform_pm->forbid_runtime_pm() : false;
+}
+
static inline bool platform_pci_bridge_d3(struct pci_dev *dev)
{
if (pci_platform_pm && pci_platform_pm->bridge_d3)
@@ -3024,7 +3030,8 @@ void pci_pm_init(struct pci_dev *dev)
u16 status;
u16 pmc;

- pm_runtime_forbid(&dev->dev);
+ if (platform_pci_forbid_runtime_pm())
+ pm_runtime_forbid(&dev->dev);
pm_runtime_set_active(&dev->dev);
pm_runtime_enable(&dev->dev);
device_enable_async_suspend(&dev->dev);
diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
index 5c5936509..d2d406ee4 100644
--- a/drivers/pci/pci.h
+++ b/drivers/pci/pci.h
@@ -71,8 +71,10 @@ int pci_bus_error_reset(struct pci_dev *dev);
* suspended) needs to be resumed to be configured for system
* wakeup.
*
+ * @forbid_runtime_pm: returns true in case of known issues breaking runtime pm
+ *
* If given platform is generally capable of power managing PCI devices, all of
- * these callbacks are mandatory.
+ * these callbacks are mandatory (except forbid_runtime_pm).
*/
struct pci_platform_pm_ops {
bool (*bridge_d3)(struct pci_dev *dev);
@@ -83,6 +85,7 @@ struct pci_platform_pm_ops {
pci_power_t (*choose_state)(struct pci_dev *dev);
int (*set_wakeup)(struct pci_dev *dev, bool enable);
bool (*need_resume)(struct pci_dev *dev);
+ bool (*forbid_runtime_pm)(void);
};

int pci_set_platform_pm(const struct pci_platform_pm_ops *ops);
--
2.29.2