Commit 30c39952 authored by Rodrigo Vivi's avatar Rodrigo Vivi
Browse files

drm/xe: Document Xe PM component 



Replace outdated information with a proper PM documentation.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.

v2: updated after Francois' feedback.
    s/grater/greater (Matt)
v3: detach D3 from runtime_pm
    remove opportunistic S0iX (Anshuman)

Cc: Matthew Auld <matthew.auld@intel.com>
Cc: Anshuman Gupta <anshuman.gupta@intel.com>
Acked-by: default avatarFrancois Dugast <francois.dugast@intel.com>
Reviewed-by: Francois Dugast <francois.dugast@intel.com> #v2
Signed-off-by: default avatarRodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: default avatarAnshuman Gupta <anshuman.gupta@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240222163937.138342-1-rodrigo.vivi@intel.com
parent a9e483dd

drivers/gpu/drm/xe/xe_pm.c

+98 −11
Original line number Diff line number Diff line
@@ -25,21 +25,47 @@ 
/**

 * 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`. 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.

 * PCI Device Suspend (D-States) - This is the opportunistic PCIe device low power

 * state D3, controlled by the PCI subsystem and ACPI with the help from the

 * runtime_pm infrastructure.

 * 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 own methods (_PR3 and _OFF)

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

 * transition by calling pci_d3cold_disable(root_pdev) before going to runtime

 * suspend. It will be based on runtime conditions such as VRAM usage for a

 * quick and low latency resume for instance.

 *

 * Also runtime_pm needs to be here from the beginning.

 * Runtime PM - This infrastructure provided by the Linux kernel allows the

 * device drivers to indicate when the can be runtime suspended, so the device

 * could be put at D3 (if supported), or allow deeper package sleep states

 * (PC-states), and/or other low level power states. Xe PM component provides

 * `xe_pm_runtime_suspend` and `xe_pm_runtime_resume` functions that PCI

 * subsystem will call before transition to/from runtime suspend.

 *

 * 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.

 * 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.

 * The main cases that need to be protected from the outer levels are: IOCTL,

 * sysfs, debugfs, dma-buf sharing, GPU execution.

 *

 * This component is not responsible for GT idleness (RC6) nor GT frequency

 * management (RPS).

 */



/**
@@ -178,6 +204,12 @@ 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)

{

	/* For now suspend/resume is only allowed with GuC */
@@ -196,6 +228,10 @@ 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;
@@ -225,6 +261,12 @@ 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;
@@ -290,6 +332,12 @@ 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;
@@ -341,22 +389,47 @@ 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 greater 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 greater 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 greater 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);
@@ -371,6 +444,13 @@ 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;
@@ -395,6 +475,13 @@ 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;