Subject: Re: [PATCH v8 04/27] cxl/pci: add check for validating capabilities

From: Jonathan Cameron <[email-masked]>
Date: Tue, 24 Dec 2024 17:15:33 +0000

On Mon, 16 Dec 2024 16:10:19 +0000
[email-masked] wrote:

> From: Alejandro Lucero <[email-masked]>
> 
> During CXL device initialization supported capabilities by the device
> are discovered. Type3 and Type2 devices have different mandatory
> capabilities and a Type2 expects a specific set including optional
> capabilities.
> 
> Add a function for checking expected capabilities against those found
> during initialization and allow those mandatory/expected capabilities to
> be a subset of the capabilities found.
> 
> Rely on this function for validating capabilities instead of when CXL
> regs are probed.
> 
> Signed-off-by: Alejandro Lucero <[email-masked]>
> Reviewed-by: Zhi Wang <[email-masked]>

Some follow on comments in how to handle bitmaps.

Jonathan

> diff --git a/drivers/cxl/pci.c b/drivers/cxl/pci.c
> index dbc1cd9bec09..1fcc53df1217 100644
> --- a/drivers/cxl/pci.c
> +++ b/drivers/cxl/pci.c
> @@ -903,6 +903,8 @@ __ATTRIBUTE_GROUPS(cxl_rcd);
>  static int cxl_pci_probe(struct pci_dev *pdev, const struct pci_device_id *id)
>  {
>  	struct pci_host_bridge *host_bridge = pci_find_host_bridge(pdev->bus);
> +	DECLARE_BITMAP(expected, CXL_MAX_CAPS);
> +	DECLARE_BITMAP(found, CXL_MAX_CAPS);
>  	struct cxl_memdev_state *mds;
>  	struct cxl_dev_state *cxlds;
>  	struct cxl_register_map map;
> @@ -964,6 +966,28 @@ static int cxl_pci_probe(struct pci_dev *pdev, const struct pci_device_id *id)
>  	if (rc)
>  		dev_dbg(&pdev->dev, "Failed to map RAS capability.\n");
>  
> +	bitmap_clear(expected, 0, CXL_MAX_CAPS);
> +
> +	/*
> +	 * These are the mandatory capabilities for a Type3 device.
> +	 * Only checking capabilities used by current Linux drivers.
> +	 */
> +	bitmap_set(expected, CXL_DEV_CAP_HDM, 1);

set_bit()  - see comments in bitmap.h, these are fine applied to bitmaps
and make more sense for setting a single bit.

> +	bitmap_set(expected, CXL_DEV_CAP_DEV_STATUS, 1);
> +	bitmap_set(expected, CXL_DEV_CAP_MAILBOX_PRIMARY, 1);
> +	bitmap_set(expected, CXL_DEV_CAP_MEMDEV, 1);
> +
> +	/*
> +	 * Checking mandatory caps are there as, at least, a subset of those
> +	 * found.
> +	 */
> +	if (!cxl_pci_check_caps(cxlds, expected, found)) {
> +		dev_err(&pdev->dev,
> +			"Expected mandatory capabilities not found: (%08lx - %08lx)\n",
> +			*expected, *found);
There are printk formats for bitmaps that should be used here. %*pb

> +		return -ENXIO;
> +	}
> +
>  	rc = cxl_pci_type3_init_mailbox(cxlds);
>  	if (rc)
>  		return rc;
> diff --git a/include/cxl/cxl.h b/include/cxl/cxl.h
> index f656fcd4945f..05f06bfd2c29 100644
> --- a/include/cxl/cxl.h
> +++ b/include/cxl/cxl.h
> @@ -37,4 +37,7 @@ void cxl_set_dvsec(struct cxl_dev_state *cxlds, u16 dvsec);
>  void cxl_set_serial(struct cxl_dev_state *cxlds, u64 serial);
>  int cxl_set_resource(struct cxl_dev_state *cxlds, struct resource res,
>  		     enum cxl_resource);
> +bool cxl_pci_check_caps(struct cxl_dev_state *cxlds,
> +			unsigned long *expected_caps,
> +			unsigned long *current_caps);
>  #endif