First off, I would change the subject to something like "Prefer CXL
_OSC to PCI _OSC for CXL host bridges". As is, it kind of suggests
that the CXL _OSC is preferred in all cases.
On Thu, Mar 31, 2022 at 10:20 PM Vishal Verma <vishal.l.verma@xxxxxxxxx> wrote:
>
> From: Dan Williams <dan.j.williams@xxxxxxxxx>
>
> OB In preparation for negotiating OS control of CXL _OSC features, do the
> minimal enabling to use CXL _OSC to handle the base PCIe feature
> negotiation. Recall that CXL _OSC is a super-set of PCIe _OSC and the
> CXL 2.0 specification mandates: "If a CXL Host Bridge device exposes CXL
> _OSC, CXL aware OSPM shall evaluate CXL _OSC and not evaluate PCIe
> _OSC."
>
> Rather than pass a boolean flag alongside @root to all the helper
> functions that need to consider PCIe specifics, add is_pcie() and
> is_cxl() helper functions to check the flavor of @root. This also
> allows for dynamic fallback to PCIe _OSC in cases where an attempt to
> use CXL _OXC fails. This can happen on CXL 1.1 platforms that publish
> ACPI0016 devices to indicate CXL host bridges, but do not publish the
> optional CXL _OSC method. CXL _OSC is mandatory for CXL 2.0 hosts.
>
> Cc: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
> Cc: "Rafael J. Wysocki" <rafael@xxxxxxxxxx>
> Cc: Robert Moore <robert.moore@xxxxxxxxx>
> Reviewed-by: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx>
> Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
> Signed-off-by: Vishal Verma <vishal.l.verma@xxxxxxxxx>
> ---
> include/linux/acpi.h | 4 +++
> include/acpi/acpi_bus.h | 6 ++++
> drivers/acpi/pci_root.c | 70 ++++++++++++++++++++++++++++++++---------
> 3 files changed, 65 insertions(+), 15 deletions(-)
>
> diff --git a/include/linux/acpi.h b/include/linux/acpi.h
> index ff4d1fdd9009..fc40da914315 100644
> --- a/include/linux/acpi.h
> +++ b/include/linux/acpi.h
> @@ -550,6 +550,10 @@ struct acpi_osc_context {
>
> acpi_status acpi_run_osc(acpi_handle handle, struct acpi_osc_context *context);
>
> +/* Number of _OSC capability DWORDS depends on bridge type */
> +#define OSC_PCI_CAPABILITY_DWORDS 3
> +#define OSC_CXL_CAPABILITY_DWORDS 5
> +
> /* Indexes into _OSC Capabilities Buffer (DWORDs 2 & 3 are device-specific) */
> #define OSC_QUERY_DWORD 0 /* DWORD 1 */
> #define OSC_SUPPORT_DWORD 1 /* DWORD 2 */
> diff --git a/include/acpi/acpi_bus.h b/include/acpi/acpi_bus.h
> index ca88c4706f2b..9413d2389711 100644
> --- a/include/acpi/acpi_bus.h
> +++ b/include/acpi/acpi_bus.h
> @@ -581,10 +581,16 @@ int unregister_acpi_bus_type(struct acpi_bus_type *);
> int acpi_bind_one(struct device *dev, struct acpi_device *adev);
> int acpi_unbind_one(struct device *dev);
>
> +enum acpi_bridge_type {
> + ACPI_BRIDGE_TYPE_PCIE = 1,
> + ACPI_BRIDGE_TYPE_CXL,
> +};
> +
> struct acpi_pci_root {
> struct acpi_device * device;
> struct pci_bus *bus;
> u16 segment;
> + int bridge_type;
> struct resource secondary; /* downstream bus range */
>
> u32 osc_support_set; /* _OSC state of support bits */
> diff --git a/drivers/acpi/pci_root.c b/drivers/acpi/pci_root.c
> index 40a74ff3fa02..5d33bc61fe44 100644
> --- a/drivers/acpi/pci_root.c
> +++ b/drivers/acpi/pci_root.c
> @@ -170,20 +170,45 @@ static void decode_osc_control(struct acpi_pci_root *root, char *msg, u32 word)
> ARRAY_SIZE(pci_osc_control_bit));
> }
>
> -static u8 pci_osc_uuid_str[] = "33DB4D5B-1FF7-401C-9657-7441C03DD766";
> +static inline bool is_pcie(struct acpi_pci_root *root)
> +{
> + return root->bridge_type == ACPI_BRIDGE_TYPE_PCIE;
> +}
>
> -static acpi_status acpi_pci_run_osc(acpi_handle handle,
> +static inline bool is_cxl(struct acpi_pci_root *root)
> +{
> + return root->bridge_type == ACPI_BRIDGE_TYPE_CXL;
> +}
> +
> +static u8 pci_osc_uuid_str[] = "33DB4D5B-1FF7-401C-9657-7441C03DD766";
> +static u8 cxl_osc_uuid_str[] = "68F2D50B-C469-4d8A-BD3D-941A103FD3FC";
> +
> +static char *to_uuid(struct acpi_pci_root *root)
> +{
> + if (is_cxl(root))
> + return cxl_osc_uuid_str;
> + return pci_osc_uuid_str;
> +}
> +
> +static int cap_length(struct acpi_pci_root *root)
> +{
> + if (is_cxl(root))
> + return sizeof(u32) * OSC_CXL_CAPABILITY_DWORDS;
> + return sizeof(u32) * OSC_PCI_CAPABILITY_DWORDS;
> +}
> +
> +static acpi_status acpi_pci_run_osc(struct acpi_pci_root *root,
> const u32 *capbuf, u32 *retval)
> {
> struct acpi_osc_context context = {
> - .uuid_str = pci_osc_uuid_str,
> + .uuid_str = to_uuid(root),
> .rev = 1,
> - .cap.length = 12,
> + .cap.length = cap_length(root),
> .cap.pointer = (void *)capbuf,
> };
> acpi_status status;
>
> - status = acpi_run_osc(handle, &context);
> + status = acpi_run_osc(root->device->handle, &context);
> if (ACPI_SUCCESS(status)) {
> *retval = acpi_osc_ctx_get_pci_control(&context);
> kfree(context.ret.pointer);
> @@ -196,7 +221,7 @@ static acpi_status acpi_pci_query_osc(struct acpi_pci_root *root,
> u32 *control)
> {
> acpi_status status;
> - u32 result, capbuf[3];
> + u32 result, capbuf[OSC_CXL_CAPABILITY_DWORDS];
>
> support |= root->osc_support_set;
>
> @@ -204,10 +229,18 @@ static acpi_status acpi_pci_query_osc(struct acpi_pci_root *root,
> capbuf[OSC_SUPPORT_DWORD] = support;
> capbuf[OSC_CONTROL_DWORD] = *control | root->osc_control_set;
>
> - status = acpi_pci_run_osc(root->device->handle, capbuf, &result);
> +retry:
> + status = acpi_pci_run_osc(root, capbuf, &result);
> if (ACPI_SUCCESS(status)) {
> root->osc_support_set = support;
> *control = result;
> + } else if (is_cxl(root)) {
> + /*
> + * CXL _OSC is optional on CXL 1.1 hosts. Fall back to PCIe _OSC
> + * upon any failure using CXL _OSC.
> + */
> + root->bridge_type = ACPI_BRIDGE_TYPE_PCIE;
> + goto retry;
> }
> return status;
> }
> @@ -338,7 +371,7 @@ static acpi_status acpi_pci_osc_control_set(acpi_handle handle, u32 *mask, u32 s
> u32 req = OSC_PCI_EXPRESS_CAPABILITY_CONTROL;
> struct acpi_pci_root *root;
> acpi_status status;
> - u32 ctrl, capbuf[3];
> + u32 ctrl, capbuf[OSC_CXL_CAPABILITY_DWORDS];
>
> if (!mask)
> return AE_BAD_PARAMETER;
> @@ -375,7 +408,7 @@ static acpi_status acpi_pci_osc_control_set(acpi_handle handle, u32 *mask, u32 s
> capbuf[OSC_QUERY_DWORD] = 0;
> capbuf[OSC_SUPPORT_DWORD] = root->osc_support_set;
> capbuf[OSC_CONTROL_DWORD] = ctrl;
> - status = acpi_pci_run_osc(handle, capbuf, mask);
> + status = acpi_pci_run_osc(root, capbuf, mask);
> if (ACPI_FAILURE(status))
> return status;
>
> @@ -454,8 +487,7 @@ static bool os_control_query_checks(struct acpi_pci_root *root, u32 support)
> return true;
> }
>
> -static void negotiate_os_control(struct acpi_pci_root *root, int *no_aspm,
> - bool is_pcie)
> +static void negotiate_os_control(struct acpi_pci_root *root, int *no_aspm)
> {
> u32 support, control = 0, requested = 0;
> acpi_status status;
> @@ -506,7 +538,7 @@ static void negotiate_os_control(struct acpi_pci_root *root, int *no_aspm,
> *no_aspm = 1;
>
> /* _OSC is optional for PCI host bridges */
> - if ((status == AE_NOT_FOUND) && !is_pcie)
> + if (status == AE_NOT_FOUND && !is_pcie(root))
> return;
>
> if (control) {
> @@ -529,7 +561,7 @@ static int acpi_pci_root_add(struct acpi_device *device,
> acpi_handle handle = device->handle;
> int no_aspm = 0;
> bool hotadd = system_state == SYSTEM_RUNNING;
> - bool is_pcie;
> + const char *acpi_hid;
>
> root = kzalloc(sizeof(struct acpi_pci_root), GFP_KERNEL);
> if (!root)
> @@ -587,8 +619,16 @@ static int acpi_pci_root_add(struct acpi_device *device,
>
> root->mcfg_addr = acpi_pci_root_get_mcfg_addr(handle);
>
> - is_pcie = strcmp(acpi_device_hid(device), "PNP0A08") == 0;
> - negotiate_os_control(root, &no_aspm, is_pcie);
> + acpi_hid = acpi_device_hid(root->device);
> + if (strcmp(acpi_hid, "PNP0A08") == 0)
> + root->bridge_type = ACPI_BRIDGE_TYPE_PCIE;
> + else if (strcmp(acpi_hid, "ACPI0016") == 0)
> + root->bridge_type = ACPI_BRIDGE_TYPE_CXL;
> + else
> + dev_warn(&device->dev, "unknown bridge type with hid: %s\n",
> + acpi_hid);
Second, because "device" is an ACPI device object and it has a _HID,
its name should include the ID in this case, so including it into the
message once more is redundant.
Also, if this is neither PCIe nor CXL, it should be a "legacy" PCI
host bridge and that is not an error, so maybe use dev_dbg("Assuming
non-PCIe host bridge\n")?
> +
> + negotiate_os_control(root, &no_aspm);
>
> /*
> * TBD: Need PCI interface for enumeration/configuration of roots.
> --
