Subject: Re: [PATCH v3 03/20] cxl/pci: add check for validating capabilities

From: Jonathan Cameron <[email-masked]>
Date: Fri, 13 Sep 2024 18:28:28 +0100

On Sat, 7 Sep 2024 09:18:19 +0100
<[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.
> 
> Rely on this function for validating capabilities instead of when CXL
> regs are probed.
> 
> Signed-off-by: Alejandro Lucero <[email-masked]>
> ---
>  drivers/cxl/core/pci.c  | 17 +++++++++++++++++
>  drivers/cxl/core/regs.c |  9 ---------
>  drivers/cxl/pci.c       | 12 ++++++++++++
>  include/linux/cxl/cxl.h |  2 ++
>  4 files changed, 31 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/cxl/core/pci.c b/drivers/cxl/core/pci.c
> index 3d6564dbda57..57370d9beb32 100644
> --- a/drivers/cxl/core/pci.c
> +++ b/drivers/cxl/core/pci.c
> @@ -7,6 +7,7 @@
>  #include <linux/pci.h>
>  #include <linux/pci-doe.h>
>  #include <linux/aer.h>
> +#include <linux/cxl/cxl.h>
>  #include <linux/cxl/pci.h>
>  #include <cxlpci.h>
>  #include <cxlmem.h>
> @@ -1077,3 +1078,19 @@ bool cxl_endpoint_decoder_reset_detected(struct cxl_port *port)
>  				     __cxl_endpoint_decoder_reset_detected);
>  }
>  EXPORT_SYMBOL_NS_GPL(cxl_endpoint_decoder_reset_detected, CXL);
> +
> +bool cxl_pci_check_caps(struct cxl_dev_state *cxlds, u32 expected_caps,
> +			u32 *current_caps)
> +{
> +	if (current_caps)
> +		*current_caps = cxlds->capabilities;

I'd split this up as setting a value in a 'check_caps' and comparisom with
a list is odd.

Also bitmaps all the way would be better.
Given you know it fits in one unsigned long you can short cut the
assignment of the bits though. Easy to extend that later if the bitmap
gets bigger.

> +
> +	dev_dbg(cxlds->dev, "Checking cxlds caps 0x%08x vs expected caps 0x%08x\n",
> +		cxlds->capabilities, expected_caps);
> +
> +	if ((cxlds->capabilities & expected_caps) != expected_caps)
> +		return false;
> +
> +	return true;
> +}
> +EXPORT_SYMBOL_NS_GPL(cxl_pci_check_caps, CXL);
> diff --git a/drivers/cxl/core/regs.c b/drivers/cxl/core/regs.c
> index 8b8abcadcb93..35f6dc97be6e 100644
> --- a/drivers/cxl/core/regs.c
> +++ b/drivers/cxl/core/regs.c
> @@ -443,15 +443,6 @@ static int cxl_probe_regs(struct cxl_register_map *map, u32 *caps)
>  	case CXL_REGLOC_RBI_MEMDEV:
>  		dev_map = &map->device_map;
>  		cxl_probe_device_regs(host, base, dev_map, caps);
> -		if (!dev_map->status.valid || !dev_map->mbox.valid ||
> -		    !dev_map->memdev.valid) {
> -			dev_err(host, "registers not found: %s%s%s\n",
> -				!dev_map->status.valid ? "status " : "",
> -				!dev_map->mbox.valid ? "mbox " : "",
> -				!dev_map->memdev.valid ? "memdev " : "");
> -			return -ENXIO;
> -		}
> -
>  		dev_dbg(host, "Probing device registers...\n");
>  		break;
>  	default:
> diff --git a/drivers/cxl/pci.c b/drivers/cxl/pci.c
> index 58f325019886..bec660357eec 100644
> --- a/drivers/cxl/pci.c
> +++ b/drivers/cxl/pci.c
> @@ -796,6 +796,7 @@ static int cxl_pci_probe(struct pci_dev *pdev, const struct pci_device_id *id)
>  	struct cxl_register_map map;
>  	struct cxl_memdev *cxlmd;
>  	int i, rc, pmu_count;
> +	u32 expected, found;
>  	bool irq_avail;
>  	u16 dvsec;
>  
> @@ -852,6 +853,17 @@ 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");
>  
> +	/* These are the mandatory capabilities for a Type3 device */
> +	expected = BIT(CXL_DEV_CAP_HDM) | BIT(CXL_DEV_CAP_DEV_STATUS) |
> +		   BIT(CXL_DEV_CAP_MAILBOX_PRIMARY) | BIT(CXL_DEV_CAP_MEMDEV);
> +
> +	if (!cxl_pci_check_caps(cxlds, expected, &found)) {
> +		dev_err(&pdev->dev,
> +			"Expected capabilities not matching with found capabilities: (%08x - %08x)\n",
> +			expected, found);
> +		return -ENXIO;
> +	}
> +
>  	rc = cxl_await_media_ready(cxlds);
>  	if (rc == 0)
>  		cxlds->media_ready = true;
> diff --git a/include/linux/cxl/cxl.h b/include/linux/cxl/cxl.h
> index 930b1b9c1d6a..4a57bf60403d 100644
> --- a/include/linux/cxl/cxl.h
> +++ b/include/linux/cxl/cxl.h
> @@ -48,4 +48,6 @@ 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, u32 expected_caps,
> +			u32 *current_caps);
>  #endif