Re: [PATCH v4 4/7] cxl/acpi: Add background worker to wait for cxl_pci and cxl_mem probe

[Dave Jiang <dave.jiang@intel.com>]

On 6/3/25 3:19 PM, Smita Koralahalli wrote:
> Introduce a waitqueue mechanism to coordinate initialization between the
> cxl_pci and cxl_mem drivers.
> 
> Launch a background worker from cxl_acpi_probe() that waits for both
> drivers to complete initialization before invoking wait_for_device_probe().
> Without this, the probe completion wait could begin prematurely, before
> the drivers are present, leading to missed updates.
> 
> Co-developed-by: Nathan Fontenot <Nathan.Fontenot@amd.com>
> Signed-off-by: Nathan Fontenot <Nathan.Fontenot@amd.com>
> Co-developed-by: Terry Bowman <terry.bowman@amd.com>
> Signed-off-by: Terry Bowman <terry.bowman@amd.com>
> Signed-off-by: Smita Koralahalli <Smita.KoralahalliChannabasappa@amd.com>
> ---
>  drivers/cxl/acpi.c         | 23 +++++++++++++++++++++++
>  drivers/cxl/core/suspend.c | 21 +++++++++++++++++++++
>  drivers/cxl/cxl.h          |  2 ++
>  3 files changed, 46 insertions(+)
> 
> diff --git a/drivers/cxl/acpi.c b/drivers/cxl/acpi.c
> index cb14829bb9be..978f63b32b41 100644
> --- a/drivers/cxl/acpi.c
> +++ b/drivers/cxl/acpi.c
> @@ -813,6 +813,24 @@ static int pair_cxl_resource(struct device *dev, void *data)
>  	return 0;
>  }
>  
> +static void cxl_softreserv_mem_work_fn(struct work_struct *work)
> +{
> +	/* Wait for cxl_pci and cxl_mem drivers to load */
> +	cxl_wait_for_pci_mem();
> +
> +	/*
> +	 * Wait for the driver probe routines to complete after cxl_pci
> +	 * and cxl_mem drivers are loaded.
> +	 */
> +	wait_for_device_probe();
> +}
> +static DECLARE_WORK(cxl_sr_work, cxl_softreserv_mem_work_fn);
> +
> +static void cxl_softreserv_mem_update(void)
> +{
> +	schedule_work(&cxl_sr_work);
> +}
> +
>  static int cxl_acpi_probe(struct platform_device *pdev)
>  {
>  	int rc;
> @@ -887,6 +905,10 @@ static int cxl_acpi_probe(struct platform_device *pdev)
>  
>  	/* In case PCI is scanned before ACPI re-trigger memdev attach */
>  	cxl_bus_rescan();
> +
> +	/* Update SOFT RESERVE resources that intersect with CXL regions */
> +	cxl_softreserv_mem_update();
> +
>  	return 0;
>  }
>  
> @@ -918,6 +940,7 @@ static int __init cxl_acpi_init(void)
>  
>  static void __exit cxl_acpi_exit(void)
>  {
> +	cancel_work_sync(&cxl_sr_work);
>  	platform_driver_unregister(&cxl_acpi_driver);
>  	cxl_bus_drain();
>  }
> diff --git a/drivers/cxl/core/suspend.c b/drivers/cxl/core/suspend.c
> index 72818a2c8ec8..c0d8f70aed56 100644
> --- a/drivers/cxl/core/suspend.c
> +++ b/drivers/cxl/core/suspend.c
> @@ -2,12 +2,15 @@
>  /* Copyright(c) 2022 Intel Corporation. All rights reserved. */
>  #include <linux/atomic.h>
>  #include <linux/export.h>
> +#include <linux/wait.h>
>  #include "cxlmem.h"
>  #include "cxlpci.h"
>  
>  static atomic_t mem_active;
>  static atomic_t pci_loaded;
>  
> +static DECLARE_WAIT_QUEUE_HEAD(cxl_wait_queue);
> +
>  bool cxl_mem_active(void)
>  {
>  	if (IS_ENABLED(CONFIG_CXL_MEM))
> @@ -19,6 +22,7 @@ bool cxl_mem_active(void)
>  void cxl_mem_active_inc(void)
>  {
>  	atomic_inc(&mem_active);
> +	wake_up(&cxl_wait_queue);
>  }
>  EXPORT_SYMBOL_NS_GPL(cxl_mem_active_inc, "CXL");
>  
> @@ -28,8 +32,25 @@ void cxl_mem_active_dec(void)
>  }
>  EXPORT_SYMBOL_NS_GPL(cxl_mem_active_dec, "CXL");
>  
> +static bool cxl_pci_loaded(void)
> +{
> +	if (IS_ENABLED(CONFIG_CXL_PCI))
> +		return atomic_read(&pci_loaded) != 0;
> +
> +	return false;
> +}
> +
>  void mark_cxl_pci_loaded(void)
>  {
>  	atomic_inc(&pci_loaded);
> +	wake_up(&cxl_wait_queue);
>  }
>  EXPORT_SYMBOL_NS_GPL(mark_cxl_pci_loaded, "CXL");
> +
> +void cxl_wait_for_pci_mem(void)
> +{
> +	if (!wait_event_timeout(cxl_wait_queue, cxl_pci_loaded() &&
> +				cxl_mem_active(), 30 * HZ))

I'm trying to understand why cxl_pci_loaded() is needed. cxl_mem_active() goes above 0 when a cxl_mem_probe() instance succeeds. cxl_mem_probe() being triggered implies that an instance of cxl_pci_probe() has been called since cxl_mem_probe() is triggered from devm_cxl_add_memdev() with memdev being added and cxl_mem driver also have been loaded. So does cxl_mem_active() not imply cxl_pci_loaded() and makes it unnecessary?

DJ


> +		pr_debug("Timeout waiting for cxl_pci or cxl_mem probing\n");
> +}
> +EXPORT_SYMBOL_NS_GPL(cxl_wait_for_pci_mem, "CXL");
> diff --git a/drivers/cxl/cxl.h b/drivers/cxl/cxl.h
> index a9ab46eb0610..1ba7d39c2991 100644
> --- a/drivers/cxl/cxl.h
> +++ b/drivers/cxl/cxl.h
> @@ -902,6 +902,8 @@ void cxl_coordinates_combine(struct access_coordinate *out,
>  
>  bool cxl_endpoint_decoder_reset_detected(struct cxl_port *port);
>  
> +void cxl_wait_for_pci_mem(void);
> +
>  /*
>   * Unit test builds overrides this to __weak, find the 'strong' version
>   * of these symbols in tools/testing/cxl/.