linux-kernel - RE: [PATCH v5 11/26] cxl/pci: Early setup RCH dport component registers from RCRB

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Message-ID: <64878293e1b01_1433ac29446@dwillia2-xfh.jf.intel.com.notmuch>
Date:   Mon, 12 Jun 2023 13:39:47 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Terry Bowman <terry.bowman@....com>, <alison.schofield@...el.com>,
        <vishal.l.verma@...el.com>, <ira.weiny@...el.com>,
        <bwidawsk@...nel.org>, <dan.j.williams@...el.com>,
        <dave.jiang@...el.com>, <Jonathan.Cameron@...wei.com>,
        <linux-cxl@...r.kernel.org>
CC:     <terry.bowman@....com>, <rrichter@....com>,
        <linux-kernel@...r.kernel.org>, <bhelgaas@...gle.com>
Subject: RE: [PATCH v5 11/26] cxl/pci: Early setup RCH dport component
 registers from RCRB

Terry Bowman wrote:
> From: Robert Richter <rrichter@....com>
> 
> CXL RAS capabilities must be enabled and accessible as soon as the CXL
> endpoint is detected in the PCI hierarchy and bound to the cxl_pci
> driver. This needs to be independent of other modules such as cxl_port
> or cxl_mem.
> 
> CXL RAS capabilities reside in the Component Registers. For an RCH
> this is determined by probing RCRB which is implemented very late once
> the CXL Memory Device is created.
> 
> Change this by moving the RCRB probe to the cxl_pci driver. Do this by
> using a new introduced function cxl_pci_find_port() similar to
> cxl_mem_find_port() to determine the involved dport by the endpoint's
> PCI handle. Plug this into the existing cxl_pci_setup_regs() function
> to setup Component Registers. Probe the RCRB in case the Component
> Registers cannot be located through the CXL Register Locator
> capability.
> 
> This unifies code and early sets up the Component Registers at the
> same time for both, VH and RCH mode. Only the cxl_pci driver is
> involved for this. This allows an early mapping of the CXL RAS
> capability registers.
> 
> Signed-off-by: Robert Richter <rrichter@....com>
> Signed-off-by: Terry Bowman <terry.bowman@....com>
> Reviewed-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>
[..]
> diff --git a/drivers/cxl/pci.c b/drivers/cxl/pci.c
> index 945ca0304d68..2975b232fcd1 100644
> --- a/drivers/cxl/pci.c
> +++ b/drivers/cxl/pci.c
> @@ -274,13 +274,48 @@ static int cxl_pci_setup_mailbox(struct cxl_dev_state *cxlds)
>  	return 0;
>  }
>  
> +/* Extract RCRB, use same function interface as cxl_find_regblock(). */
> +static int cxl_rcrb_get_comp_regs(struct pci_dev *pdev,
> +				  enum cxl_regloc_type type,
> +				  struct cxl_register_map *map)
> +{
> +	struct cxl_dport *dport;
> +	resource_size_t component_reg_phys;
> +
> +	memset(map, 0, sizeof(*map));
> +	map->dev = &pdev->dev;
> +	map->resource = CXL_RESOURCE_NONE;
> +
> +	if (type != CXL_REGLOC_RBI_COMPONENT)
> +		return -ENODEV;
> +
> +	if (!cxl_pci_find_port(pdev, &dport) || !dport->rch)
> +		return -ENXIO;

I noticed while reviewing a later patch that this pattern leaks the port
reference from cxl_pci_find_port().

I.e. this needs to do:

	port = cxl_pci_find_port(...);
	if (!port)
		return -ENXIO;
	if (!dport->rch)
		goto out;
	...
out:
	put_device(&port->dev);