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

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Message-ID: <ZHoOhdiCu5O/C+TV@rric.localdomain>
Date:   Fri, 2 Jun 2023 17:45:09 +0200
From:   Robert Richter <rrichter@....com>
To:     Jonathan Cameron <Jonathan.Cameron@...wei.com>
CC:     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>, <linux-cxl@...r.kernel.org>,
        <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 01.06.23 13:59:31, Jonathan Cameron wrote:
> 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.
> */
> ?

Will change that.

Thanks for review,

-Robert

> 
> > +	 */
> >  	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);
>