[RFC 02/34] drm/xe: Document Xe PM component

[Francois Dugast]

On Fri, Jan 26, 2024 at 03:30:11PM -0500, Rodrigo Vivi wrote:
> Replace outdated information with a proper PM documentation.
> Already establish the rules for the runtime PM get and put that
> Xe needs to follow.
> 
> Also add missing function documentation to all the "exported" functions.
> 
> Cc: Anshuman Gupta <anshuman.gupta at intel.com>
> Signed-off-by: Rodrigo Vivi <rodrigo.vivi at intel.com>

Hi,

Very helpful summary, I think the level of detail is spot on. Minor nits below.

Acked-by: Francois Dugast <francois.dugast at intel.com>

> ---
>  drivers/gpu/drm/xe/xe_pm.c | 107 +++++++++++++++++++++++++++++++++----
>  1 file changed, 96 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/gpu/drm/xe/xe_pm.c b/drivers/gpu/drm/xe/xe_pm.c
> index d5f219796d7e..bd35fe9f6227 100644
> --- a/drivers/gpu/drm/xe/xe_pm.c
> +++ b/drivers/gpu/drm/xe/xe_pm.c
> @@ -25,21 +25,45 @@
>  /**
>   * DOC: Xe Power Management
>   *
> - * Xe PM shall be guided by the simplicity.
> - * Use the simplest hook options whenever possible.
> - * Let's not reinvent the runtime_pm references and hooks.
> - * Shall have a clear separation of display and gt underneath this component.
> + * Xe PM implements the main routines for both system level suspend states and
> + * for the opportunistic runtime suspend states.
>   *
> - * What's next:
> + * System Level Suspend (S-States) - In general this is OS initiated suspend
> + * driven by ACPI for achieving S0ix (a.k.a. S2idle, freeze), S3 (suspend to ram),
> + * S4 (disk). The main functions here are `xe_pm_suspend` and `xe_pm_resume` that

The sentence seems a bit long to me, maybe s/that/. They/?

> + * are the main point for the suspend to and resume from these states.
>   *
> - * For now s2idle and s3 are only working in integrated devices. The next step
> - * is to iterate through all VRAM's BO backing them up into the system memory
> - * before allowing the system suspend.
> + * Runtime Suspend (D-States) - This is the opportunistic PCIe device low power
> + * state D3. Xe PM component provides `xe_pm_runtime_suspend` and
> + * `xe_pm_runtime_resume` systems that PCI subsystem will call before transition
> + * to D3. Also, Xe PM provides get and put functions that Xe driver will use to
> + * indicate activity. In order to avoid locking complications with the memory
> + * management, whenever possible, these get and put functions needs to be called
> + * from the higher/outer levels.
>   *
> - * Also runtime_pm needs to be here from the beginning.
> + * The main cases that need to be protected from the outer levels are: IOCLT,

s/IOCLT/IOCTL/

> + * sysfs, debugfs, dma-buf sharing, GPU execution.
>   *
> - * RC6/RPS are also critical PM features. Let's start with GuCRC and GuC SLPC
> - * and no wait boost. Frequency optimizations should come on a next stage.
> + * PCI D3 is special and can mean D3hot, where Vcc power is on for keeping memory
> + * alive and quicker low latency resume or D3Cold where Vcc power is off for
> + * better power savings.
> + * The Vcc control of PCI hierarchy can only be controlled at the PCI root port
> + * level, while the device driver can be behind multiple bridges/switches and
> + * paired with other devices. For this reason, the PCI subsystem cannot perform
> + * the transition towards D3Cold. The lowest runtime PM possible from the PCI
> + * subsystem is D3hot. Then, if all these paired devices in the same root port
> + * are in D3hot, ACPI will assist here and run its _PR3 and _OFF methods to

If the "_PR3 and _OFF" reference is needed, maybe provide a pointer to those?

> + * perform the transition from D3hot to D3cold. Xe may disallow this transition

How?

Francois

> + * based on runtime conditions such as VRAM usage for a quick and low latency
> + * resume for instance.
> + *
> + * Intel systems are capable of taking the system to S0ix when devices are on
> + * D3hot through the runtime PM. This is also called as 'opportunistic-S0iX'.
> + * But in this case, the `xe_pm_suspend` and `xe_pm_resume` won't be called for
> + * S0ix.
> + *
> + * This component is no responsible for GT idleness (RC6) nor GT frequency
> + * management (RPS).
>   */
>  
>  /**
> @@ -169,6 +193,12 @@ void xe_pm_init_early(struct xe_device *xe)
>  	drmm_mutex_init(&xe->drm, &xe->mem_access.vram_userfault.lock);
>  }
>  
> +/**
> + * xe_pm_init - Initialize Xe Power Management
> + * @xe: xe device instance
> + *
> + * This component is responsible for System and Device sleep states.
> + */
>  void xe_pm_init(struct xe_device *xe)
>  {
>  	struct pci_dev *pdev = to_pci_dev(xe->drm.dev);
> @@ -189,6 +219,10 @@ void xe_pm_init(struct xe_device *xe)
>  	xe_pm_runtime_init(xe);
>  }
>  
> +/**
> + * xe_pm_runtime_fini - Finalize Runtime PM
> + * @xe: xe device instance
> + */
>  void xe_pm_runtime_fini(struct xe_device *xe)
>  {
>  	struct device *dev = xe->drm.dev;
> @@ -218,6 +252,12 @@ struct task_struct *xe_pm_read_callback_task(struct xe_device *xe)
>  	return READ_ONCE(xe->pm_callback_task);
>  }
>  
> +/**
> + * xe_pm_runtime_suspend - Prepare our device for D3hot/D3Cold
> + * @xe: xe device instance
> + *
> + * Returns 0 for success, negative error code otherwise.
> + */
>  int xe_pm_runtime_suspend(struct xe_device *xe)
>  {
>  	struct xe_bo *bo, *on;
> @@ -283,6 +323,12 @@ int xe_pm_runtime_suspend(struct xe_device *xe)
>  	return err;
>  }
>  
> +/**
> + * xe_pm_runtime_resume - Waking up from D3hot/D3Cold
> + * @xe: xe device instance
> + *
> + * Returns 0 for success, negative error code otherwise.
> + */
>  int xe_pm_runtime_resume(struct xe_device *xe)
>  {
>  	struct xe_gt *gt;
> @@ -334,22 +380,47 @@ int xe_pm_runtime_resume(struct xe_device *xe)
>  	return err;
>  }
>  
> +/**
> + * xe_pm_runtime_get - Get a runtime_pm reference and resume synchronously
> + * @xe: xe device instance
> + *
> + * Returns: Any number grater than or equal to 0 for success, negative error
> + * code otherwise.
> + */
>  int xe_pm_runtime_get(struct xe_device *xe)
>  {
>  	return pm_runtime_get_sync(xe->drm.dev);
>  }
>  
> +/**
> + * xe_pm_runtime_put - Put the runtime_pm reference back and mark as idle
> + * @xe: xe device instance
> + *
> + * Returns: Any number grater than or equal to 0 for success, negative error
> + * code otherwise.
> + */
>  int xe_pm_runtime_put(struct xe_device *xe)
>  {
>  	pm_runtime_mark_last_busy(xe->drm.dev);
>  	return pm_runtime_put(xe->drm.dev);
>  }
>  
> +/**
> + * xe_pm_runtime_get_if_active - Get a runtime_pm reference if device active
> + * @xe: xe device instance
> + *
> + * Returns: Any number grater than or equal to 0 for success, negative error
> + * code otherwise.
> + */
>  int xe_pm_runtime_get_if_active(struct xe_device *xe)
>  {
>  	return pm_runtime_get_if_active(xe->drm.dev, true);
>  }
>  
> +/**
> + * xe_pm_assert_unbounded_bridge - Disable PM on unbounded pcie parent bridge
> + * @xe: xe device instance
> + */
>  void xe_pm_assert_unbounded_bridge(struct xe_device *xe)
>  {
>  	struct pci_dev *pdev = to_pci_dev(xe->drm.dev);
> @@ -364,6 +435,13 @@ void xe_pm_assert_unbounded_bridge(struct xe_device *xe)
>  	}
>  }
>  
> +/**
> + * xe_pm_set_vram_threshold - Set a vram threshold for allowing/blocking D3Cold
> + * @xe: xe device instance
> + * @threshold: VRAM size in bites for the D3cold threshold
> + *
> + * Returns 0 for success, negative error code otherwise.
> + */
>  int xe_pm_set_vram_threshold(struct xe_device *xe, u32 threshold)
>  {
>  	struct ttm_resource_manager *man;
> @@ -388,6 +466,13 @@ int xe_pm_set_vram_threshold(struct xe_device *xe, u32 threshold)
>  	return 0;
>  }
>  
> +/**
> + * xe_pm_d3cold_allowed_toggle - Check conditions to toggle d3cold.allowed
> + * @xe: xe device instance
> + *
> + * To be called during runtime_pm idle callback.
> + * Check for all the D3Cold conditions ahead of runtime suspend.
> + */
>  void xe_pm_d3cold_allowed_toggle(struct xe_device *xe)
>  {
>  	struct ttm_resource_manager *man;
> -- 
> 2.43.0
>