Re: [PATCH v4 1/3] CXL, PCIE: Add cxl_rcrb_addr file to dport_dev

[Jonathan Cameron <Jonathan.Cameron@Huawei.com>]

On Thu, 7 Sep 2023 14:19:54 -0500
Ben Cheatham <Benjamin.Cheatham@amd.com> wrote:

> Add cxl_rcrb_addr to the dport_dev (normally represented by a pcie
> device) for CXL RCH root ports. The file will print the RCRB base
> MMIO address of the root port when read and will be used by
> users looking to inject CXL EINJ error types for RCH hosts.
> 
> Signed-off-by: Ben Cheatham <Benjamin.Cheatham@amd.com>

Can we use is_visble to control presence of the attribute rather than
race condition special that is dynamic addition of a sysfs file.

You are adding the file to the linked device which is a bit odd.
Why there rather than in the portX?

I'd also normally expect the docs to call out the non-link path for that
device which is somewhere in the PCI topology I think.

> ---
>  Documentation/ABI/testing/sysfs-bus-cxl |  8 ++++++
>  drivers/cxl/acpi.c                      |  2 ++
>  drivers/cxl/core/port.c                 | 33 +++++++++++++++++++++++++
>  drivers/cxl/cxl.h                       |  2 ++
>  4 files changed, 45 insertions(+)
> 
> diff --git a/Documentation/ABI/testing/sysfs-bus-cxl b/Documentation/ABI/testing/sysfs-bus-cxl
> index 087f762ebfd5..a7d169235543 100644
> --- a/Documentation/ABI/testing/sysfs-bus-cxl
> +++ b/Documentation/ABI/testing/sysfs-bus-cxl
> @@ -177,6 +177,14 @@ Description:
>  		integer reflects the hardware port unique-id used in the
>  		hardware decoder target list.
>  
> +What:		/sys/bus/cxl/devices/portX/dportY/cxl_rcrb_addr
> +Date:		August, 2023
> +KernelVersion:	v6.6
> +Contact:	linux-cxl@vger.kernel.org
> +Description:
> +		(RO) The 'cxl_rcrb_addr' device file gives the MMIO base address
> +		of the RCRB of the corresponding CXL 1.1 downstream port. Only
> +		present for CXL 1.1 dports.
>  
>  What:		/sys/bus/cxl/devices/decoderX.Y
>  Date:		June, 2021
> diff --git a/drivers/cxl/acpi.c b/drivers/cxl/acpi.c
> index d1c559879dcc..3e2ca946bf47 100644
> --- a/drivers/cxl/acpi.c
> +++ b/drivers/cxl/acpi.c
> @@ -676,6 +676,8 @@ static int cxl_acpi_probe(struct platform_device *pdev)
>  	if (IS_ERR(root_port))
>  		return PTR_ERR(root_port);
>  
> +	set_cxl_root(root_port);
> +
>  	rc = bus_for_each_dev(adev->dev.bus, NULL, root_port,
>  			      add_host_bridge_dport);
>  	if (rc < 0)
> diff --git a/drivers/cxl/core/port.c b/drivers/cxl/core/port.c
> index 724be8448eb4..001ab8742e21 100644
> --- a/drivers/cxl/core/port.c
> +++ b/drivers/cxl/core/port.c
> @@ -875,6 +875,14 @@ struct cxl_port *find_cxl_root(struct cxl_port *port)
>  }
>  EXPORT_SYMBOL_NS_GPL(find_cxl_root, CXL);
>  
> +static struct cxl_port *cxl_root;
> +
> +void set_cxl_root(struct cxl_port *root_port)
> +{
> +	cxl_root = root_port;
> +}
> +EXPORT_SYMBOL_NS_GPL(set_cxl_root, CXL);
> +
>  static struct cxl_dport *find_dport(struct cxl_port *port, int id)
>  {
>  	struct cxl_dport *dport;
> @@ -930,11 +938,30 @@ static void cond_cxl_root_unlock(struct cxl_port *port)
>  		device_unlock(&port->dev);
>  }
>  
> +static ssize_t cxl_rcrb_addr_show(struct device *dev,
> +				  struct device_attribute *attr, char *buf)
> +{
> +	struct cxl_dport *dport;
> +
> +	if (!cxl_root)
> +		return -ENODEV;
> +
> +	dport = cxl_find_dport_by_dev(cxl_root, dev);
> +	if (!dport)
> +		return -ENODEV;
> +
> +	return sysfs_emit(buf, "0x%llx\n", (u64) dport->rcrb.base);
> +}
> +DEVICE_ATTR_RO(cxl_rcrb_addr);
> +
>  static void cxl_dport_remove(void *data)
>  {
>  	struct cxl_dport *dport = data;
>  	struct cxl_port *port = dport->port;
>  
> +	if (dport->rch)
> +		device_remove_file(dport->dport_dev, &dev_attr_cxl_rcrb_addr);
> +
>  	xa_erase(&port->dports, (unsigned long) dport->dport_dev);
>  	put_device(dport->dport_dev);
>  }
> @@ -1021,6 +1048,12 @@ __devm_cxl_add_dport(struct cxl_port *port, struct device *dport_dev,
>  	if (rc)
>  		return ERR_PTR(rc);
>  
> +	if (dport->rch && dport->rcrb.base != CXL_RESOURCE_NONE) {
> +		rc = device_create_file(dport_dev, &dev_attr_cxl_rcrb_addr);
> +		if (rc)
> +			return ERR_PTR(rc);
> +	}
> +
>  	return dport;
>  }
>  
> diff --git a/drivers/cxl/cxl.h b/drivers/cxl/cxl.h
> index 76d92561af29..4d5bce4bae7e 100644
> --- a/drivers/cxl/cxl.h
> +++ b/drivers/cxl/cxl.h
> @@ -690,6 +690,8 @@ struct cxl_port *devm_cxl_add_port(struct device *host,
>  				   resource_size_t component_reg_phys,
>  				   struct cxl_dport *parent_dport);
>  struct cxl_port *find_cxl_root(struct cxl_port *port);
> +void set_cxl_root(struct cxl_port *root_port);
> +
>  int devm_cxl_enumerate_ports(struct cxl_memdev *cxlmd);
>  void cxl_bus_rescan(void);
>  void cxl_bus_drain(void);