linux-kernel - Re: [PATCH v4 10/23] cxl/port: Store the port's Component Register mappings in struct cxl

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Message-ID: <20230601140603.00007ba2@Huawei.com>
Date:   Thu, 1 Jun 2023 14:06:03 +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 10/23] cxl/port: Store the port's Component Register
 mappings in struct cxl_port

On Tue, 23 May 2023 18:22:01 -0500
Terry Bowman <terry.bowman@....com> wrote:

> From: Robert Richter <rrichter@....com>
> 
> CXL capabilities are stored in the Component Registers. To use them,
> the specific I/O ranges of the capabilities must be determined by
> probing the registers. For this, the whole Component Register range
> needs to be mapped temporarily to detect the offset and length of a
> capability range.
> 
> In order to use more than one capability of a component (e.g. RAS and
> HDM) the Component Register are probed and its mappings created
> multiple times. This also causes overlapping I/O ranges as the whole
> Component Register range must be mapped again while a capability's I/O
> range is already mapped.
> 
> Different capabilities cannot be setup at the same time. E.g. the RAS
> capability must be made available as soon as the PCI driver is bound,
> the HDM decoder is setup later during port enumeration. Moreover,
> during early setup it is still unknown if a certain capability is
> needed. A central capability setup is therefore not possible,
> capabilities must be individually enabled once needed during
> initialization.
> 
> To avoid a duplicate register probe and overlapping I/O mappings, only
> probe the Component Registers one time and store the Component
> Register mapping in struct port. The stored mappings can be used later
> to iomap the capability register range when enabling the capability,
> which will be implemented in a follow-on patch.
> 
> Signed-off-by: Robert Richter <rrichter@....com>
> Signed-off-by: Terry Bowman <terry.bowman@....com>
Some minor comments...


> ---
>  drivers/cxl/core/port.c | 26 ++++++++++++++++++++++++++
>  drivers/cxl/cxl.h       |  2 ++
>  2 files changed, 28 insertions(+)
> 
> diff --git a/drivers/cxl/core/port.c b/drivers/cxl/core/port.c
> index eff91f141fde..34e929f1723b 100644
> --- a/drivers/cxl/core/port.c
> +++ b/drivers/cxl/core/port.c
> @@ -686,6 +686,28 @@ static struct cxl_port *cxl_port_alloc(struct device *uport,
>  	return ERR_PTR(rc);
>  }
>  
> +static int cxl_setup_comp_regs(struct device *dev, struct cxl_register_map *map,
> +			       resource_size_t component_reg_phys)
> +{
> +	if (component_reg_phys == CXL_RESOURCE_NONE)
> +		return -ENODEV;
> +
> +	memset(map, 0, sizeof(*map));
> +	map->dev = dev;
> +	map->reg_type = CXL_REGLOC_RBI_COMPONENT;
> +	map->resource = component_reg_phys;
> +	map->max_size = CXL_COMPONENT_REG_BLOCK_SIZE;
setting most elements. Maybe
	*map = (struct cxl_register_map) {
		.dev = ...
etc is cleaner and effectively the same thing.
	};
> +
> +	return cxl_setup_regs(map);
> +}
> +
> +static inline int cxl_port_setup_regs(struct cxl_port *port,
> +				      resource_size_t component_reg_phys)
> +{
> +	return cxl_setup_comp_regs(&port->dev, &port->comp_map,
> +				   component_reg_phys);
> +}
> +
>  static struct cxl_port *__devm_cxl_add_port(struct device *host,
>  					    struct device *uport,
>  					    resource_size_t component_reg_phys,
> @@ -709,6 +731,10 @@ static struct cxl_port *__devm_cxl_add_port(struct device *host,
>  	if (rc)
>  		goto err;
>  
> +	rc = cxl_port_setup_regs(port, component_reg_phys);
> +	if (rc && rc != -ENODEV)
> +		goto err;

I'd add a comment on why not being present is fine here.


> +
>  	rc = device_add(dev);
>  	if (rc)
>  		goto err;
> diff --git a/drivers/cxl/cxl.h b/drivers/cxl/cxl.h
> index e5ae5f4e6669..c76e1f84ba61 100644
> --- a/drivers/cxl/cxl.h
> +++ b/drivers/cxl/cxl.h
> @@ -552,6 +552,7 @@ struct cxl_dax_region {
>   * @regions: cxl_region_ref instances, regions mapped by this port
>   * @parent_dport: dport that points to this port in the parent
>   * @decoder_ida: allocator for decoder ids
> + * @comp_map: component register capability mappings
>   * @nr_dports: number of entries in @dports
>   * @hdm_end: track last allocated HDM decoder instance for allocation ordering
>   * @commit_end: cursor to track highest committed decoder for commit ordering
> @@ -571,6 +572,7 @@ struct cxl_port {
>  	struct xarray regions;
>  	struct cxl_dport *parent_dport;
>  	struct ida decoder_ida;
> +	struct cxl_register_map comp_map;
>  	int nr_dports;
>  	int hdm_end;
>  	int commit_end;