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Message-ID: <20220611001217.GA639674@bhelgaas>
Date: Fri, 10 Jun 2022 19:12:17 -0500
From: Bjorn Helgaas <helgaas@...nel.org>
To: Rajvi Jingar <rajvi.jingar@...ux.intel.com>
Cc: rafael.j.wysocki@...el.com, bhelgaas@...gle.com,
david.e.box@...ux.intel.com, linux-pci@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org
Subject: Re: [PATCH v7 2/2] PCI/PM: Disable PTM on all devices
On Wed, Jun 08, 2022 at 05:10:07PM -0700, Rajvi Jingar wrote:
> On receiving a PTM Request from a downstream device, if PTM is disabled
> on the root port, as per PCIe specification, such request would cause
> an Unsupported Request error. So disable PTM for any downstream devices.
> PTM state needs to be saved before disabling it to be restored later.
>
> Set ptm_enabled from 'struct pci_dev' to 0 in pci_ptm_disable() and
> it is used in pci_save_state() before saving PTM state to avoid
> double save.
>
> Fixes: a697f072f5da ("PCI: Disable PTM during suspend to save power")
> Signed-off-by: Rajvi Jingar <rajvi.jingar@...ux.intel.com>
> Suggested-by: David E. Box <david.e.box@...ux.intel.com>
> ---
> v1 -> v2: add Fixes tag in commit message
> v2 -> v3: move changelog after "---" marker
> v3 -> v4: add "---" marker after changelog
> v4 -> v5: move pci_disable_ptm() out of the pci_dev->state_saved check.
> disable PTM for all devices, not just root ports.
> v5 -> v6: move pci_disable_ptm() to pci_pm_suspend()
> set pci_dev->ptm_enabled to 0 in pci_ptm_disable() and it is
> used in pci_save_state() before saving PTM state to avoid
> double save.
> v6 -> v7: add #ifdef CONFIG_PCIE_PTM in pci_save_state() before saving
> PTM state
> ---
> drivers/pci/pci-driver.c | 21 ++++++++++++++++++++-
> drivers/pci/pci.c | 28 +++++++++++++---------------
> drivers/pci/pcie/ptm.c | 1 +
> 3 files changed, 34 insertions(+), 16 deletions(-)
>
> diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
> index 1f64de3e5280..db4d7835d7ae 100644
> --- a/drivers/pci/pci-driver.c
> +++ b/drivers/pci/pci-driver.c
> @@ -803,14 +803,33 @@ static int pci_pm_suspend(struct device *dev)
> pci_dev_adjust_pme(pci_dev);
> }
>
> + /*
> + * If a PTM Requester is put in a low-power state, a PTM Responder
> + * upstream from it may also be put in a low-power state. Putting a
> + * Port in D1, D2, or D3hot does not prohibit it from sending or
> + * responding to PTM Requests. We want to disable PTM on Responders
> + * when they are in a low-power state. Per 6.21.3, a PTM Requester
> + * must not be enabled when the upstream PTM Responder is disabled.
> + * Therefore, we must disable all PTM on all downstream PTM
> + * Requesters before disabling it on the PTM Responder, e.g., a Root
> + * Port.
> + *
> + * Also, to restore the PTM state, it needs to be saved before
> + * disabling it for all devices.
> + */
> + pci_save_ptm_state(pci_dev);
> + pci_disable_ptm(pci_dev);
I think this is a little bit too magical. The PTM disable doesn't
really fit here in pci_pm_suspend(). It's more like the wakeup
configuration done by pci_pm_suspend_noirq() in
pci_prepare_to_sleep().
IIUC, the reason it's here in pci_pm_suspend() is because of the weird
nvme thing where nvme_suspend() puts the device in a device-specific
low-power flavor of D0 and subsequent config accesses take it out of
that low-power situation [1].
I don't think this is a maintainable situation because there's nothing
about this pci_disable_ptm() that says "this cannot be done after
pm->suspend()". That's a completely nvme-specific thing that we can't
deduce from the code and are likely to break in the future.
We *do* have the rule that if the driver sets pdev->state_saved
(normally by calling pci_save_state()), it means the driver is
responsible for *all* the device state, even the standard config space
that the PCI core would normally handle.
When the driver does set pdev->state_saved, I don't think
pci_pm_suspend_noirq() actually touches the device itself, and I'm a
little more comfortable relying on that assumption.
If this nvme weirdness plays a part here, I think the commit log and
probably a comment really should mention what's going on because it's
just feels fragile.
[1] https://lore.kernel.org/r/CAJZ5v0iNaAd=yP3DgDVVpffKU6kt+nSpPeqxWJyRddaX5K4FRA@mail.gmail.com
> if (pm->suspend) {
> pci_power_t prev = pci_dev->current_state;
> int error;
>
> error = pm->suspend(dev);
> suspend_report_result(dev, pm->suspend, error);
> - if (error)
> + if (error) {
> + pci_restore_ptm_state(pci_dev);
> return error;
> + }
>
> if (!pci_dev->state_saved && pci_dev->current_state != PCI_D0
> && pci_dev->current_state != PCI_UNKNOWN) {
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index cfaf40a540a8..3e9dcb1bbffa 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -1669,7 +1669,15 @@ int pci_save_state(struct pci_dev *dev)
> pci_save_ltr_state(dev);
> pci_save_dpc_state(dev);
> pci_save_aer_state(dev);
> - pci_save_ptm_state(dev);
> +#ifdef CONFIG_PCIE_PTM
> + /*
> + * PCI PM core disables PTM during suspend and saves PTM state before
> + * that to be able to restore the ptm state restored later. So PCI core
> + * needs this check to avoid double save.
> + */
> + if (dev->ptm_enabled)
> + pci_save_ptm_state(dev);
> +#endif
This ptm_enabled check doesn't fit with the rest of the function and
the semantics are fairly complicated.
> return pci_save_vc_state(dev);
> }
> EXPORT_SYMBOL(pci_save_state);
> @@ -2710,24 +2718,12 @@ int pci_prepare_to_sleep(struct pci_dev *dev)
> if (target_state == PCI_POWER_ERROR)
> return -EIO;
>
> - /*
> - * There are systems (for example, Intel mobile chips since Coffee
> - * Lake) where the power drawn while suspended can be significantly
> - * reduced by disabling PTM on PCIe root ports as this allows the
> - * port to enter a lower-power PM state and the SoC to reach a
> - * lower-power idle state as a whole.
> - */
> - if (pci_pcie_type(dev) == PCI_EXP_TYPE_ROOT_PORT)
> - pci_disable_ptm(dev);
> -
> pci_enable_wake(dev, target_state, wakeup);
>
> error = pci_set_power_state(dev, target_state);
>
> - if (error) {
> + if (error)
> pci_enable_wake(dev, target_state, false);
> - pci_restore_ptm_state(dev);
> - }
>
> return error;
> }
> @@ -2775,8 +2771,10 @@ int pci_finish_runtime_suspend(struct pci_dev *dev)
> * port to enter a lower-power PM state and the SoC to reach a
> * lower-power idle state as a whole.
> */
> - if (pci_pcie_type(dev) == PCI_EXP_TYPE_ROOT_PORT)
> + if (pci_pcie_type(dev) == PCI_EXP_TYPE_ROOT_PORT) {
> + pci_save_ptm_state(dev);
> pci_disable_ptm(dev);
> + }
>
> __pci_enable_wake(dev, target_state, pci_dev_run_wake(dev));
>
> diff --git a/drivers/pci/pcie/ptm.c b/drivers/pci/pcie/ptm.c
> index 368a254e3124..746e29779c27 100644
> --- a/drivers/pci/pcie/ptm.c
> +++ b/drivers/pci/pcie/ptm.c
> @@ -44,6 +44,7 @@ void pci_disable_ptm(struct pci_dev *dev)
> pci_read_config_word(dev, ptm + PCI_PTM_CTRL, &ctrl);
> ctrl &= ~(PCI_PTM_CTRL_ENABLE | PCI_PTM_CTRL_ROOT);
> pci_write_config_word(dev, ptm + PCI_PTM_CTRL, ctrl);
> + dev->ptm_enabled = 0;
This looks like a bug fix that could be in a separate patch.
> }
>
> void pci_save_ptm_state(struct pci_dev *dev)
I think something like the sketch below would fit better in the power
management framework. PTM disable is closely related to device power
states, so I tried to put it as close as possible to the power state
transitions. I'm sure there are things missing and things I'm
overlooking:
diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index cfaf40a540a8..4dcd0c7381b9 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -2705,28 +2705,21 @@ int pci_prepare_to_sleep(struct pci_dev *dev)
{
bool wakeup = device_may_wakeup(&dev->dev);
pci_power_t target_state = pci_target_state(dev, wakeup);
+ bool ptm = pcie_ptm_enabled(dev);
int error;
if (target_state == PCI_POWER_ERROR)
return -EIO;
- /*
- * There are systems (for example, Intel mobile chips since Coffee
- * Lake) where the power drawn while suspended can be significantly
- * reduced by disabling PTM on PCIe root ports as this allows the
- * port to enter a lower-power PM state and the SoC to reach a
- * lower-power idle state as a whole.
- */
- if (pci_pcie_type(dev) == PCI_EXP_TYPE_ROOT_PORT)
- pci_disable_ptm(dev);
-
+ pci_disable_ptm(dev);
pci_enable_wake(dev, target_state, wakeup);
error = pci_set_power_state(dev, target_state);
if (error) {
pci_enable_wake(dev, target_state, false);
- pci_restore_ptm_state(dev);
+ if (ptm)
+ pci_enable_ptm(dev);
}
return error;
@@ -2762,6 +2755,7 @@ EXPORT_SYMBOL(pci_back_from_sleep);
int pci_finish_runtime_suspend(struct pci_dev *dev)
{
pci_power_t target_state;
+ bool ptm = pcie_ptm_enabled(dev);
int error;
target_state = pci_target_state(dev, device_can_wakeup(&dev->dev));
@@ -2778,13 +2772,15 @@ int pci_finish_runtime_suspend(struct pci_dev *dev)
if (pci_pcie_type(dev) == PCI_EXP_TYPE_ROOT_PORT)
pci_disable_ptm(dev);
+ pci_disable_ptm(dev);
__pci_enable_wake(dev, target_state, pci_dev_run_wake(dev));
error = pci_set_power_state(dev, target_state);
if (error) {
pci_enable_wake(dev, target_state, false);
- pci_restore_ptm_state(dev);
+ if (ptm)
+ pci_enable_ptm(dev);
}
return error;
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