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Date:   Tue, 12 Jan 2021 18:48:40 +0000
From:   Jonathan Cameron <Jonathan.Cameron@...wei.com>
To:     Ben Widawsky <ben.widawsky@...el.com>
CC:     <linux-cxl@...r.kernel.org>,
        Vishal Verma <vishal.l.verma@...el.com>,
        <linux-kernel@...r.kernel.org>, <linux-pci@...r.kernel.org>,
        "linux-acpi@...r.kernel.org, Ira Weiny" <ira.weiny@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        "Kelley, Sean V" <sean.v.kelley@...el.com>,
        Rafael Wysocki <rafael.j.wysocki@...el.com>,
        Bjorn Helgaas <helgaas@...nel.org>,
        Jon Masters <jcm@...masters.org>,
        Chris Browy <cbrowy@...ry-design.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        "Christoph Hellwig" <hch@...radead.org>,
        <daniel.lll@...baba-inc.com>
Subject: Re: [RFC PATCH v3 03/16] cxl/acpi: add OSC support

On Mon, 11 Jan 2021 14:51:07 -0800
Ben Widawsky <ben.widawsky@...el.com> wrote:

> From: Vishal Verma <vishal.l.verma@...el.com>
> 
> Add support to advertise OS capabilities, and request OS control for CXL
> features using the ACPI _OSC mechanism. Advertise support for all
> possible CXL features, and attempt to request control for all possible
> features.
> 
> Based on a patch by Sean Kelley.
> 
> Signed-off-by: Vishal Verma <vishal.l.verma@...el.com>
> Signed-off-by: Ben Widawsky <ben.widawsky@...el.com>

Whilst I understand the reasoning behind not just sharing this code with PCI,
it might be worth adding a comment to the code somewhere on that.

Otherwise, I suspect you'll very rapidly see patches cleaning up this duplication :)

Otherwise LGTM.

J
> ---
>  Documentation/cxl/memory-devices.rst |  15 ++
>  drivers/cxl/acpi.c                   | 260 ++++++++++++++++++++++++++-
>  drivers/cxl/acpi.h                   |  20 +++
>  3 files changed, 292 insertions(+), 3 deletions(-)
> 
> diff --git a/Documentation/cxl/memory-devices.rst b/Documentation/cxl/memory-devices.rst
> index aa4262280c67..6ce88f9d5f4f 100644
> --- a/Documentation/cxl/memory-devices.rst
> +++ b/Documentation/cxl/memory-devices.rst
> @@ -13,3 +13,18 @@ Driver Infrastructure
>  =====================
>  
>  This sections covers the driver infrastructure for a CXL memory device.
> +
> +ACPI CXL
> +--------
> +
> +.. kernel-doc:: drivers/cxl/acpi.c
> +   :doc: cxl acpi
> +
> +.. kernel-doc:: drivers/cxl/acpi.c
> +   :internal:
> +
> +External Interfaces
> +===================
> +
> +.. kernel-doc:: drivers/cxl/acpi.c
> +   :export:
> diff --git a/drivers/cxl/acpi.c b/drivers/cxl/acpi.c
> index 0f1ba9b3f1ed..af9c0dfdee20 100644
> --- a/drivers/cxl/acpi.c
> +++ b/drivers/cxl/acpi.c
> @@ -11,7 +11,258 @@
>  #include <linux/pci.h>
>  #include "acpi.h"
>  
> -/*
> +/**
> + * DOC: cxl acpi
> + *
> + * ACPI _OSC setup: The exported function cxl_bus_acquire() sets up ACPI
> + * Operating System Capabilities (_OSC) for the CXL bus. It declares support
> + * for all CXL capabilities, and attempts to request control for all possible
> + * capabilities. The resulting support and control sets are saved in global
> + * variables cxl_osc_support_set and cxl_osc_control_set. The internal
> + * functions cxl_osc_declare_support(), and cxl_osc_request_control() can be
> + * used to update the support and control sets in accordance with the ACPI
> + * rules for _OSC evaluation - most importantly, capabilities already granted
> + * should not be rescinded by either the OS or firmware.
> + */
> +
> +static u32 cxl_osc_support_set;
> +static u32 cxl_osc_control_set;
> +static DEFINE_MUTEX(acpi_desc_lock);
> +
> +struct pci_osc_bit_struct {
> +	u32 bit;
> +	char *desc;
> +};
> +
> +static struct pci_osc_bit_struct cxl_osc_support_bit[] = {
> +	{ CXL_OSC_PORT_REG_ACCESS_SUPPORT, "CXLPortRegAccess" },
> +	{ CXL_OSC_PORT_DEV_REG_ACCESS_SUPPORT, "CXLPortDevRegAccess" },
> +	{ CXL_OSC_PER_SUPPORT, "CXLProtocolErrorReporting" },
> +	{ CXL_OSC_NATIVE_HP_SUPPORT, "CXLNativeHotPlug" },
> +};
> +
> +static struct pci_osc_bit_struct cxl_osc_control_bit[] = {
> +	{ CXL_OSC_MEM_ERROR_CONTROL, "CXLMemErrorReporting" },
> +};
> +
> +static u8 cxl_osc_uuid_str[] = "68F2D50B-C469-4d8A-BD3D-941A103FD3FC";
> +
> +static void decode_osc_bits(struct device *dev, char *msg, u32 word,
> +			    struct pci_osc_bit_struct *table, int size)
> +{
> +	char buf[80];
> +	int i, len = 0;
> +	struct pci_osc_bit_struct *entry;
> +
> +	buf[0] = '\0';
> +	for (i = 0, entry = table; i < size; i++, entry++)
> +		if (word & entry->bit)
> +			len += scnprintf(buf + len, sizeof(buf) - len, "%s%s",
> +					 len ? " " : "", entry->desc);
> +
> +	dev_info(dev, "_OSC: %s [%s]\n", msg, buf);
> +}
> +
> +static void decode_cxl_osc_support(struct device *dev, char *msg, u32 word)
> +{
> +	decode_osc_bits(dev, msg, word, cxl_osc_support_bit,
> +			ARRAY_SIZE(cxl_osc_support_bit));
> +}
> +
> +static void decode_cxl_osc_control(struct device *dev, char *msg, u32 word)
> +{
> +	decode_osc_bits(dev, msg, word, cxl_osc_control_bit,
> +			ARRAY_SIZE(cxl_osc_control_bit));
> +}
> +
> +static acpi_status acpi_cap_run_osc(acpi_handle handle, const u32 *capbuf,
> +				    u8 *uuid_str, u32 *retval)
> +{
> +	struct acpi_osc_context context = {
> +		.uuid_str = uuid_str,
> +		.rev = 1,
> +		.cap.length = 20,
> +		.cap.pointer = (void *)capbuf,
> +	};
> +	acpi_status status;
> +
> +	status = acpi_run_osc(handle, &context);
> +	if (ACPI_SUCCESS(status)) {
> +		/* pointer + offset to DWORD 5 */
> +		*retval = *((u32 *)(context.ret.pointer + 16));
> +		kfree(context.ret.pointer);
> +	}
> +	return status;
> +}
> +
> +static acpi_status cxl_query_osc(acpi_handle handle, u32 support, u32 *control)
> +{
> +	struct acpi_pci_root *root;
> +	acpi_status status;
> +	u32 result, capbuf[5];
> +
> +	root = acpi_pci_find_root(handle);
> +	if (!root)
> +		return -ENXIO;
> +
> +	support &= CXL_OSC_SUPPORT_VALID_MASK;
> +	support |= cxl_osc_support_set;
> +
> +	capbuf[OSC_QUERY_DWORD] = OSC_QUERY_ENABLE;
> +	capbuf[PCI_OSC_SUPPORT_DWORD] = root->osc_support_set;
> +	capbuf[PCI_OSC_CONTROL_DWORD] = root->osc_control_set;
> +	capbuf[CXL_OSC_SUPPORT_DWORD] = support;
> +	if (control) {
> +		*control &= CXL_OSC_CONTROL_VALID_MASK;
> +		capbuf[CXL_OSC_CONTROL_DWORD] = *control | cxl_osc_control_set;
> +	} else {
> +		/* Run _OSC query only with existing controls. */
> +		capbuf[CXL_OSC_CONTROL_DWORD] = cxl_osc_control_set;
> +	}
> +
> +	status = acpi_cap_run_osc(handle, capbuf, cxl_osc_uuid_str, &result);
> +	if (ACPI_SUCCESS(status)) {
> +		cxl_osc_support_set = support;
> +		if (control)
> +			*control = result;
> +	}
> +	return status;
> +}
> +
> +/**
> + * cxl_osc_declare_support - Declare support for CXL root _OSC features.
> + * @handle: ACPI device handle for the PCI root bridge (or PCIe Root Complex).
> + * @flags: The _OSC bits to declare support for.
> + *
> + * The PCI specific DWORDS are obtained from the pci root port device, and
> + * used as-is. The resulting CXL support set is saved in cxl_osc_support_set.
> + * Any future calls to this are forced to be strictly incremental from the
> + * existing cxl_osc_support_set.
> + */
> +static acpi_status cxl_osc_declare_support(acpi_handle handle, u32 flags)
> +{
> +	acpi_status status;
> +
> +	mutex_lock(&acpi_desc_lock);
> +	status = cxl_query_osc(handle, flags, NULL);
> +	mutex_unlock(&acpi_desc_lock);
> +	return status;
> +}
> +
> +/**
> + * cxl_osc_request_control - Request control of CXL root _OSC features.
> + * @adev: ACPI device for the PCI root bridge (or PCIe Root Complex).
> + * @mask: Mask of _OSC bits to request control of, place to store control mask.
> + * @req: Mask of _OSC bits the control of is essential to the caller.
> + *
> + * The PCI specific DWORDS are obtained from the pci root port device, and
> + * used as-is. The resulting CXL control set is saved in cxl_osc_control_set.
> + * Any future calls to this are forced to be strictly incremental from the
> + * existing cxl_osc_control_set.
> + */
> +static acpi_status cxl_osc_request_control(struct acpi_device *adev, u32 *mask,
> +					   u32 req)
> +{
> +	acpi_handle handle = adev->handle;
> +	struct device *dev = &adev->dev;
> +	struct acpi_pci_root *root;
> +	acpi_status status = AE_OK;
> +	u32 ctrl, capbuf[5];
> +
> +	if (!mask)
> +		return AE_BAD_PARAMETER;
> +
> +	ctrl = *mask & CXL_OSC_MEM_ERROR_CONTROL;
> +	if ((ctrl & req) != req)
> +		return AE_TYPE;
> +
> +	root = acpi_pci_find_root(handle);
> +	if (!root)
> +		return -ENXIO;
> +
> +	mutex_lock(&acpi_desc_lock);
> +
> +	*mask = ctrl | cxl_osc_control_set;
> +	/* No need to evaluate _OSC if the control was already granted. */
> +	if ((cxl_osc_control_set & ctrl) == ctrl)
> +		goto out;
> +
> +	/* Need to check the available controls bits before requesting them. */
> +	while (*mask) {
> +		status = cxl_query_osc(handle, cxl_osc_support_set, mask);
> +		if (ACPI_FAILURE(status))
> +			goto out;
> +		if (ctrl == *mask)
> +			break;
> +		decode_cxl_osc_control(dev, "platform does not support",
> +				       ctrl & ~(*mask));
> +		ctrl = *mask;
> +	}
> +
> +	if ((ctrl & req) != req) {
> +		decode_cxl_osc_control(dev,
> +				       "not requesting control; platform does not support",
> +				       req & ~(ctrl));
> +		status = AE_SUPPORT;
> +		goto out;
> +	}
> +
> +	capbuf[OSC_QUERY_DWORD] = 0;
> +	capbuf[PCI_OSC_SUPPORT_DWORD] = root->osc_support_set;
> +	capbuf[PCI_OSC_CONTROL_DWORD] = root->osc_control_set;
> +	capbuf[CXL_OSC_SUPPORT_DWORD] = cxl_osc_support_set;
> +	capbuf[CXL_OSC_CONTROL_DWORD] = ctrl;
> +	status = acpi_cap_run_osc(handle, capbuf, cxl_osc_uuid_str, mask);
> +	if (ACPI_SUCCESS(status))
> +		cxl_osc_control_set = *mask;
> +out:
> +	mutex_unlock(&acpi_desc_lock);
> +	return status;
> +}
> +
> +static int cxl_negotiate_osc(struct acpi_device *adev)
> +{
> +	u32 cxl_support, cxl_control, requested;
> +	acpi_handle handle = adev->handle;
> +	struct device *dev = &adev->dev;
> +	acpi_status status;
> +
> +	/* Declare support for everything */
> +	cxl_support = CXL_OSC_SUPPORT_VALID_MASK;
> +	decode_cxl_osc_support(dev, "OS supports", cxl_support);
> +	status = cxl_osc_declare_support(handle, cxl_support);
> +	if (ACPI_FAILURE(status)) {
> +		dev_info(dev, "CXL_OSC failed (%s)\n",
> +			 acpi_format_exception(status));
> +		return -ENXIO;
> +	}
> +
> +	/* Request control for everything */
> +	cxl_control = CXL_OSC_CONTROL_VALID_MASK;
> +	requested = cxl_control;
> +	status = cxl_osc_request_control(adev, &cxl_control,
> +					 CXL_OSC_MEM_ERROR_CONTROL);
> +	if (ACPI_SUCCESS(status)) {
> +		decode_cxl_osc_control(dev, "OS now controls", cxl_control);
> +	} else {
> +		decode_cxl_osc_control(dev, "OS requested", requested);
> +		decode_cxl_osc_control(dev, "platform willing to grant",
> +				       cxl_control);
> +		dev_info(dev, "_OSC failed (%s)\n",
> +			 acpi_format_exception(status));
> +	}
> +	return 0;
> +}
> +
> +/**
> + * cxl_bus_acquire - Perform platform-specific bus operations
> + * @pdev: pci_dev associated with the CXL device
> + *
> + * This performs bus-specific operations such as ACPI _OSC to ensure that
> + * the bus is 'prepared'. Since the CXL definition of _OSC depends on the
> + * existing PCI _OSC DWORDS in 'Arg3', pull those in from the pci root port
> + * device, and merge those into the new CXL-augmented _OSC calls.
> + *
>   * If/when CXL support is defined by other platform firmware the kernel
>   * will need a mechanism to select between the platform specific version
>   * of this routine, until then, hard-code ACPI assumptions
> @@ -21,6 +272,7 @@ int cxl_bus_acquire(struct pci_dev *pdev)
>  	struct acpi_device *adev;
>  	struct pci_dev *root_port;
>  	struct device *root;
> +	int rc;
>  
>  	root_port = pcie_find_root_port(pdev);
>  	if (!root_port)
> @@ -34,9 +286,11 @@ int cxl_bus_acquire(struct pci_dev *pdev)
>  	if (!adev)
>  		return -ENXIO;
>  
> -	/* TODO: OSC enabling */
> +	rc = cxl_negotiate_osc(adev);
> +	if (rc)
> +		dev_err(&pdev->dev, "Failed to negotiate OSC\n");
>  
> -	return 0;
> +	return rc;
>  }
>  EXPORT_SYMBOL_GPL(cxl_bus_acquire);
>  
> diff --git a/drivers/cxl/acpi.h b/drivers/cxl/acpi.h
> index d638f8886ab7..6ef154021745 100644
> --- a/drivers/cxl/acpi.h
> +++ b/drivers/cxl/acpi.h
> @@ -12,4 +12,24 @@ struct cxl_acpi_desc {
>  
>  int cxl_bus_acquire(struct pci_dev *pci_dev);
>  
> +/* Indexes into _OSC Capabilities Buffer */
> +#define PCI_OSC_SUPPORT_DWORD			1	/* DWORD 2 */
> +#define PCI_OSC_CONTROL_DWORD			2	/* DWORD 3 */
> +#define CXL_OSC_SUPPORT_DWORD			3	/* DWORD 4 */
> +#define CXL_OSC_CONTROL_DWORD			4	/* DWORD 5 */
> +
> +/* CXL Host Bridge _OSC: Capabilities DWORD 4: Support Field */
> +#define CXL_OSC_PORT_REG_ACCESS_SUPPORT		0x00000001
> +#define CXL_OSC_PORT_DEV_REG_ACCESS_SUPPORT	0x00000002
> +#define CXL_OSC_PER_SUPPORT			0x00000004
> +#define CXL_OSC_NATIVE_HP_SUPPORT		0x00000008
> +#define CXL_OSC_SUPPORT_VALID_MASK		(CXL_OSC_PORT_REG_ACCESS_SUPPORT |	\
> +						 CXL_OSC_PORT_DEV_REG_ACCESS_SUPPORT |	\
> +						 CXL_OSC_PER_SUPPORT |			\
> +						 CXL_OSC_NATIVE_HP_SUPPORT)
> +
> +/* CXL Host Bridge _OSC: Capabilities DWORD 5: Control Field */
> +#define CXL_OSC_MEM_ERROR_CONTROL		0x00000001
> +#define CXL_OSC_CONTROL_VALID_MASK		(CXL_OSC_MEM_ERROR_CONTROL)
> +
>  #endif	/* __CXL_ACPI_H__ */

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