Re: [RFC PATCH 2/4] PCI/CXL: Populate and insert/remove pdev->coh_resource[]

[Bowman, Terry]

On 10/5/2026 2:02 AM, Ankit Agrawal wrote:
> On systems with precommitted HDM decoders, the firmware programs
> the decoders before any software runs. This range also stays constant
> over the runs.
> 
> Snapshot precommitted CXL HDM decoder ranges into a new
> pdev->coh_resource[] array, so later code has a known-good source for
> a device coherent (CXL) windows without re-scanning decoder
> registers.
> 
> Signed-off-by: Ankit Agrawal <ankita@xxxxxxxxxx>
> Assisted-by: Claude:sonnet-5
> ---
>  drivers/cxl/core/resource.c | 52 ++++++++++++++++++++++++++++++++++++-
>  include/linux/pci.h         | 14 ++++++++++
>  2 files changed, 65 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/cxl/core/resource.c b/drivers/cxl/core/resource.c
> index 3422139ae3ab..4d2082c8e321 100644
> --- a/drivers/cxl/core/resource.c
> +++ b/drivers/cxl/core/resource.c
> @@ -404,6 +404,46 @@ static struct cxl_hdm_info *cxl_pci_hdm_read_info(struct pci_dev *pdev,
>  	return ERR_PTR(pcibios_err_to_errno(rc));
>  }
>  
> +/*
> + * Snapshot committed decoders into pdev->coh_resource[] which is called
> + * once per pdev before any driver can bind, so a populated entry is
> + * always firmware-committed and not driver-committed.
> + *
> + * Insert each entry into iomem_resource for /proc/iomem visibility and
> + * conflict detection.
> + */
> +static void cxl_populate_coh_resource(struct pci_dev *pdev,
> +				      struct cxl_hdm_info *info)
> +{
> +	int count = min(info->decoder_count, PCI_CXL_MAX_COHERENT_RANGES);
> +
> +	for (int i = 0; i < count; i++) {
> +		struct cxl_decoder_config *config = &info->settings[i].config;
> +		struct resource *res = &pdev->coh_resource[i];
> +		struct resource *conflict;
> +
> +		if (!(config->flags & CXL_DECODER_F_ENABLE))
> +			continue;
> +
> +		*res = DEFINE_RES_NAMED_DESC(config->hpa_range.start,
> +					     range_len(&config->hpa_range),
> +					     "CXL coherent memory",
> +					     IORESOURCE_MEM, IORES_DESC_NONE);
> +

On platforms using Normalized Addressing the Endpoint decoders contain DPA ranges. This 
patch will then record DPA ranges as a result. Translating this requires call to prm_cxl_dpa_spa() ?
The challenge is the PRM in drivers/cxl/core/atl.c may not be initialized this early.

> +		conflict = insert_resource_conflict(&iomem_resource, res);
> +		if (conflict) {
> +			pci_warn(pdev,
> +				 "CXL coherent range: decoder%d %pR conflicts with %s %pR, leaving unpopulated\n",
> +				 i, res, conflict->name, conflict);
> +			memset(res, 0, sizeof(*res));
> +			continue;
> +		}
> +


- Terry

> +		pci_info(pdev, "CXL coherent range: decoder%d precommitted, populated %pR\n",
> +			 i, res);
> +	}
> +}
> +
>  static int __pci_cxl_hdm_cache_init(struct pci_dev *pdev)
>  {
>  	struct cxl_register_map map = { };
> @@ -442,8 +482,10 @@ static int __pci_cxl_hdm_cache_init(struct pci_dev *pdev)
>  	struct cxl_hdm_info *info __free(kfree) = read_info;
>  	guard(rwsem_write)(&cxl_rwsem.dpa);
>  	/* Another initializer may have published while we read MMIO. */
> -	if (!pdev->hdm)
> +	if (!pdev->hdm) {
> +		cxl_populate_coh_resource(pdev, info);
>  		pdev->hdm = no_free_ptr(info);
> +	}
>  
>  	return 0;
>  }
> @@ -466,6 +508,14 @@ void pci_cxl_hdm_cache_release(struct pci_dev *pdev)
>  	info = pdev->hdm;
>  	/* Unpublish before freeing so subsequent readers cannot use stale state. */
>  	pdev->hdm = NULL;
> +
> +	for (int i = 0; i < PCI_CXL_MAX_COHERENT_RANGES; i++) {
> +		struct resource *res = &pdev->coh_resource[i];
> +
> +		if (res->parent)
> +			remove_resource(res);
> +	}
> +
>  	kfree(info);
>  }
>  
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index b00f5f38f77d..ce724d067fd2 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -148,6 +148,13 @@ enum {
>  	DEVICE_COUNT_RESOURCE = PCI_NUM_RESOURCES,
>  };
>  
> +/*
> + * Max CXL HDM decoders tracked per endpoint in pci_dev->coh_resource[].
> + * CXL 3.1 spec section 8.2.4.20.1 - CXL HDM Decoder Capability Register,
> + * mention a max of 10 decoders for a CXL device.
> + */
> +#define PCI_CXL_MAX_COHERENT_RANGES 10
> +
>  /**
>   * enum pci_interrupt_pin - PCI INTx interrupt values
>   * @PCI_INTERRUPT_UNKNOWN: Unknown or unassigned interrupt
> @@ -572,6 +579,13 @@ struct pci_dev {
>  #endif
>  #ifdef CONFIG_CXL_RESET
>  	struct cxl_hdm_info *hdm;	/* CXL HDM decoder state */
> +	/*
> +	 * Precommitted CXL HDM decoder coherent ranges, snapshotted before
> +	 * any driver binds. One entry per decoder index. Only written by
> +	 * pci_cxl_hdm_cache_init()/_release(), outside any bound driver's
> +	 * read window.
> +	 */
> +	struct resource coh_resource[PCI_CXL_MAX_COHERENT_RANGES];
>  #endif
>  #ifdef CONFIG_PCI_NPEM
>  	struct npem	*npem;		/* Native PCIe Enclosure Management */