linux-kernel - Re: [PATCH v4 09/23] cxl/pci: Early setup RCH dport component registers from RCRB

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Message-ID: <20230601135931.000046fa@Huawei.com>
Date:   Thu, 1 Jun 2023 13:59:31 +0100
From:   Jonathan Cameron <Jonathan.Cameron@...wei.com>
To:     Terry Bowman <terry.bowman@....com>
CC:     <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>,
        <linux-cxl@...r.kernel.org>, <rrichter@....com>,
        <linux-kernel@...r.kernel.org>, <bhelgaas@...gle.com>
Subject: Re: [PATCH v4 09/23] cxl/pci: Early setup RCH dport component
 registers from RCRB

On Tue, 23 May 2023 18:22:00 -0500
Terry Bowman <terry.bowman@....com> 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>

One minor wording suggestion inline. I'm don't really care
that much about it though, so.

Reviewed-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>


> diff --git a/drivers/cxl/pci.c b/drivers/cxl/pci.c
> index 945ca0304d68..54c486cd65dd 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;
> +
> +	component_reg_phys = cxl_probe_rcrb(&pdev->dev, dport->rcrb.base,
> +					    NULL, CXL_RCRB_UPSTREAM);
> +	if (component_reg_phys == CXL_RESOURCE_NONE)
> +		return -ENXIO;
> +
> +	map->resource = component_reg_phys;
> +	map->reg_type = type;
> +	map->max_size = CXL_COMPONENT_REG_BLOCK_SIZE;
> +
> +	return 0;
> +}
> +
>  static int cxl_pci_setup_regs(struct pci_dev *pdev, enum cxl_regloc_type type,
>  			      struct cxl_register_map *map)
>  {
>  	int rc;
>  
> +	/*
> +	 * If the Register Locator DVSEC does not contain the
> +	 * Component Registers, try to extract them from the RCRB if
> +	 * it is an RCH.

My instinct here was to wonder why having said 'if it is an RCH'
you don't seem to be checking that first.  Perhaps
change this text to something like.
* Component Registers, assume it is an RCH and try to extra them
* from an RCRB.
*/
?

> +	 */
>  	rc = cxl_find_regblock(pdev, type, map);
> -	if (rc)
> +	if (rc && cxl_rcrb_get_comp_regs(pdev, type, map))
>  		return rc;
>  
>  	return cxl_setup_regs(map);