xhci: Add infrastructure for host-specific LPM policies.

The choice of U1 and U2 timeouts for USB 3.0 Link Power Management (LPM)
is highly host controller specific.  Here are a few examples of why it's
host specific:

 1. Setting the U1/U2 timeout too short may cause the link to go into
    U1/U2 in between service intervals, which some hosts may tolerate,
    and some may not.

 2. The host controller has to modify its bus schedule in order to take
    into account the Maximum Exit Latency (MEL) to bring all the links
    from the host to the device into U0.  If the MEL is too big, and it
    takes too long to bring the links into an active state, the host
    controller may not be able to service periodic endpoints in time.

 3. Host controllers may also have scheduling limitations that force
    them to disable U1 or U2 if a USB device is behind too many tiers of
    hubs.

We could take an educated guess at what U1/U2 timeouts may work for a
particular host controller.  However, that would result in a binary
search on every new configuration or alt setting installation, with
multiple failed Evaluate Context commands.  Worse, the host may blindly
accept the timeouts and just fail to update its schedule for U1/U2 exit
latencies, which could result in randomly delayed periodic transfers.

Since we don't want to cause jitter in periodic transfers, or delay
config/alt setting changes too much, lay down a framework that xHCI
vendors can extend in order to add their own U1/U2 timeout policies.

To extend the framework, they will need to:

 - Modify the PCI init code to add a new xhci->quirk for their host, and
   set the XHCI_LPM_SUPPORT quirk flag.
 - Add their own vendor-specific hooks, like the ones that will be added
   in xhci_call_host_update_timeout_for_endpoint() and
   xhci_check_tier_policy()
 - Make the LPM enable/disable methods call those functions based on the
   xhci->quirk for their host.

An example will be provided for the Intel xHCI host controller in the
next patch.

Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>

3 files changed, 335 insertions, 0 deletions

diff --git a/drivers/usb/host/xhci-pci.c b/drivers/usb/host/xhci-pci.c
index 19e8921..890ba73 100644
--- a/drivers/usb/host/xhci-pci.c
+++ b/drivers/usb/host/xhci-pci.c
@@ -170,6 +170,13 @@ static int xhci_pci_probe(struct pci_dev *dev, const struct pci_device_id *id)
 	if (retval)
 		goto put_usb3_hcd;
 	/* Roothub already marked as USB 3.0 speed */
+
+	/* We know the LPM timeout algorithms for this host, let the USB core
+	 * enable and disable LPM for devices under the USB 3.0 roothub.
+	 */
+	if (xhci->quirks & XHCI_LPM_SUPPORT)
+		hcd_to_bus(xhci->shared_hcd)->root_hub->lpm_capable = 1;
+
 	return 0;
 
 put_usb3_hcd:
@@ -293,6 +300,8 @@ static const struct hc_driver xhci_pci_hc_driver = {
 	 */
 	.update_device =        xhci_update_device,
 	.set_usb2_hw_lpm =	xhci_set_usb2_hardware_lpm,
+	.enable_usb3_lpm_timeout =	xhci_enable_usb3_lpm_timeout,
+	.disable_usb3_lpm_timeout =	xhci_disable_usb3_lpm_timeout,
 };
 
 /*-------------------------------------------------------------------------*/
diff --git a/drivers/usb/host/xhci.c b/drivers/usb/host/xhci.c
index 05034f3..518d002 100644
--- a/drivers/usb/host/xhci.c
+++ b/drivers/usb/host/xhci.c
@@ -3837,6 +3837,325 @@ int xhci_set_usb2_hardware_lpm(struct usb_hcd *hcd,
 	return 0;
 }
 
+/*---------------------- USB 3.0 Link PM functions ------------------------*/
+
+static u16 xhci_get_timeout_no_hub_lpm(struct usb_device *udev,
+		enum usb3_link_state state)
+{
+	unsigned long long sel;
+	unsigned long long pel;
+	unsigned int max_sel_pel;
+	char *state_name;
+
+	switch (state) {
+	case USB3_LPM_U1:
+		/* Convert SEL and PEL stored in nanoseconds to microseconds */
+		sel = DIV_ROUND_UP(udev->u1_params.sel, 1000);
+		pel = DIV_ROUND_UP(udev->u1_params.pel, 1000);
+		max_sel_pel = USB3_LPM_MAX_U1_SEL_PEL;
+		state_name = "U1";
+		break;
+	case USB3_LPM_U2:
+		sel = DIV_ROUND_UP(udev->u2_params.sel, 1000);
+		pel = DIV_ROUND_UP(udev->u2_params.pel, 1000);
+		max_sel_pel = USB3_LPM_MAX_U2_SEL_PEL;
+		state_name = "U2";
+		break;
+	default:
+		dev_warn(&udev->dev, "%s: Can't get timeout for non-U1 or U2 state.\n",
+				__func__);
+		return -EINVAL;
+	}
+
+	if (sel <= max_sel_pel && pel <= max_sel_pel)
+		return USB3_LPM_DEVICE_INITIATED;
+
+	if (sel > max_sel_pel)
+		dev_dbg(&udev->dev, "Device-initiated %s disabled "
+				"due to long SEL %llu ms\n",
+				state_name, sel);
+	else
+		dev_dbg(&udev->dev, "Device-initiated %s disabled "
+				"due to long PEL %llu\n ms",
+				state_name, pel);
+	return USB3_LPM_DISABLED;
+}
+
+static u16 xhci_call_host_update_timeout_for_endpoint(struct xhci_hcd *xhci,
+		struct usb_device *udev,
+		struct usb_endpoint_descriptor *desc,
+		enum usb3_link_state state,
+		u16 *timeout)
+{
+	return USB3_LPM_DISABLED;
+}
+
+static int xhci_update_timeout_for_endpoint(struct xhci_hcd *xhci,
+		struct usb_device *udev,
+		struct usb_endpoint_descriptor *desc,
+		enum usb3_link_state state,
+		u16 *timeout)
+{
+	u16 alt_timeout;
+
+	alt_timeout = xhci_call_host_update_timeout_for_endpoint(xhci, udev,
+		desc, state, timeout);
+
+	/* If we found we can't enable hub-initiated LPM, or
+	 * the U1 or U2 exit latency was too high to allow
+	 * device-initiated LPM as well, just stop searching.
+	 */
+	if (alt_timeout == USB3_LPM_DISABLED ||
+			alt_timeout == USB3_LPM_DEVICE_INITIATED) {
+		*timeout = alt_timeout;
+		return -E2BIG;
+	}
+	if (alt_timeout > *timeout)
+		*timeout = alt_timeout;
+	return 0;
+}
+
+static int xhci_update_timeout_for_interface(struct xhci_hcd *xhci,
+		struct usb_device *udev,
+		struct usb_host_interface *alt,
+		enum usb3_link_state state,
+		u16 *timeout)
+{
+	int j;
+
+	for (j = 0; j < alt->desc.bNumEndpoints; j++) {
+		if (xhci_update_timeout_for_endpoint(xhci, udev,
+					&alt->endpoint[j].desc, state, timeout))
+			return -E2BIG;
+		continue;
+	}
+	return 0;
+}
+
+static int xhci_check_tier_policy(struct xhci_hcd *xhci,
+		struct usb_device *udev,
+		enum usb3_link_state state)
+{
+	return -EINVAL;
+}
+
+/* Returns the U1 or U2 timeout that should be enabled.
+ * If the tier check or timeout setting functions return with a non-zero exit
+ * code, that means the timeout value has been finalized and we shouldn't look
+ * at any more endpoints.
+ */
+static u16 xhci_calculate_lpm_timeout(struct usb_hcd *hcd,
+			struct usb_device *udev, enum usb3_link_state state)
+{
+	struct xhci_hcd *xhci = hcd_to_xhci(hcd);
+	struct usb_host_config *config;
+	char *state_name;
+	int i;
+	u16 timeout = USB3_LPM_DISABLED;
+
+	if (state == USB3_LPM_U1)
+		state_name = "U1";
+	else if (state == USB3_LPM_U2)
+		state_name = "U2";
+	else {
+		dev_warn(&udev->dev, "Can't enable unknown link state %i\n",
+				state);
+		return timeout;
+	}
+
+	if (xhci_check_tier_policy(xhci, udev, state) < 0)
+		return timeout;
+
+	/* Gather some information about the currently installed configuration
+	 * and alternate interface settings.
+	 */
+	if (xhci_update_timeout_for_endpoint(xhci, udev, &udev->ep0.desc,
+			state, &timeout))
+		return timeout;
+
+	config = udev->actconfig;
+	if (!config)
+		return timeout;
+
+	for (i = 0; i < USB_MAXINTERFACES; i++) {
+		struct usb_driver *driver;
+		struct usb_interface *intf = config->interface[i];
+
+		if (!intf)
+			continue;
+
+		/* Check if any currently bound drivers want hub-initiated LPM
+		 * disabled.
+		 */
+		if (intf->dev.driver) {
+			driver = to_usb_driver(intf->dev.driver);
+			if (driver && driver->disable_hub_initiated_lpm) {
+				dev_dbg(&udev->dev, "Hub-initiated %s disabled "
+						"at request of driver %s\n",
+						state_name, driver->name);
+				return xhci_get_timeout_no_hub_lpm(udev, state);
+			}
+		}
+
+		/* Not sure how this could happen... */
+		if (!intf->cur_altsetting)
+			continue;
+
+		if (xhci_update_timeout_for_interface(xhci, udev,
+					intf->cur_altsetting,
+					state, &timeout))
+			return timeout;
+	}
+	return timeout;
+}
+
+/*
+ * Issue an Evaluate Context command to change the Maximum Exit Latency in the
+ * slot context.  If that succeeds, store the new MEL in the xhci_virt_device.
+ */
+static int xhci_change_max_exit_latency(struct xhci_hcd *xhci,
+			struct usb_device *udev, u16 max_exit_latency)
+{
+	struct xhci_virt_device *virt_dev;
+	struct xhci_command *command;
+	struct xhci_input_control_ctx *ctrl_ctx;
+	struct xhci_slot_ctx *slot_ctx;
+	unsigned long flags;
+	int ret;
+
+	spin_lock_irqsave(&xhci->lock, flags);
+	if (max_exit_latency == xhci->devs[udev->slot_id]->current_mel) {
+		spin_unlock_irqrestore(&xhci->lock, flags);
+		return 0;
+	}
+
+	/* Attempt to issue an Evaluate Context command to change the MEL. */
+	virt_dev = xhci->devs[udev->slot_id];
+	command = xhci->lpm_command;
+	xhci_slot_copy(xhci, command->in_ctx, virt_dev->out_ctx);
+	spin_unlock_irqrestore(&xhci->lock, flags);
+
+	ctrl_ctx = xhci_get_input_control_ctx(xhci, command->in_ctx);
+	ctrl_ctx->add_flags |= cpu_to_le32(SLOT_FLAG);
+	slot_ctx = xhci_get_slot_ctx(xhci, command->in_ctx);
+	slot_ctx->dev_info2 &= cpu_to_le32(~((u32) MAX_EXIT));
+	slot_ctx->dev_info2 |= cpu_to_le32(max_exit_latency);
+
+	xhci_dbg(xhci, "Set up evaluate context for LPM MEL change.\n");
+	xhci_dbg(xhci, "Slot %u Input Context:\n", udev->slot_id);
+	xhci_dbg_ctx(xhci, command->in_ctx, 0);
+
+	/* Issue and wait for the evaluate context command. */
+	ret = xhci_configure_endpoint(xhci, udev, command,
+			true, true);
+	xhci_dbg(xhci, "Slot %u Output Context:\n", udev->slot_id);
+	xhci_dbg_ctx(xhci, virt_dev->out_ctx, 0);
+
+	if (!ret) {
+		spin_lock_irqsave(&xhci->lock, flags);
+		virt_dev->current_mel = max_exit_latency;
+		spin_unlock_irqrestore(&xhci->lock, flags);
+	}
+	return ret;
+}
+
+static int calculate_max_exit_latency(struct usb_device *udev,
+		enum usb3_link_state state_changed,
+		u16 hub_encoded_timeout)
+{
+	unsigned long long u1_mel_us = 0;
+	unsigned long long u2_mel_us = 0;
+	unsigned long long mel_us = 0;
+	bool disabling_u1;
+	bool disabling_u2;
+	bool enabling_u1;
+	bool enabling_u2;
+
+	disabling_u1 = (state_changed == USB3_LPM_U1 &&
+			hub_encoded_timeout == USB3_LPM_DISABLED);
+	disabling_u2 = (state_changed == USB3_LPM_U2 &&
+			hub_encoded_timeout == USB3_LPM_DISABLED);
+
+	enabling_u1 = (state_changed == USB3_LPM_U1 &&
+			hub_encoded_timeout != USB3_LPM_DISABLED);
+	enabling_u2 = (state_changed == USB3_LPM_U2 &&
+			hub_encoded_timeout != USB3_LPM_DISABLED);
+
+	/* If U1 was already enabled and we're not disabling it,
+	 * or we're going to enable U1, account for the U1 max exit latency.
+	 */
+	if ((udev->u1_params.timeout != USB3_LPM_DISABLED && !disabling_u1) ||
+			enabling_u1)
+		u1_mel_us = DIV_ROUND_UP(udev->u1_params.mel, 1000);
+	if ((udev->u2_params.timeout != USB3_LPM_DISABLED && !disabling_u2) ||
+			enabling_u2)
+		u2_mel_us = DIV_ROUND_UP(udev->u2_params.mel, 1000);
+
+	if (u1_mel_us > u2_mel_us)
+		mel_us = u1_mel_us;
+	else
+		mel_us = u2_mel_us;
+	/* xHCI host controller max exit latency field is only 16 bits wide. */
+	if (mel_us > MAX_EXIT) {
+		dev_warn(&udev->dev, "Link PM max exit latency of %lluus "
+				"is too big.\n", mel_us);
+		return -E2BIG;
+	}
+	return mel_us;
+}
+
+/* Returns the USB3 hub-encoded value for the U1/U2 timeout. */
+int xhci_enable_usb3_lpm_timeout(struct usb_hcd *hcd,
+			struct usb_device *udev, enum usb3_link_state state)
+{
+	struct xhci_hcd	*xhci;
+	u16 hub_encoded_timeout;
+	int mel;
+	int ret;
+
+	xhci = hcd_to_xhci(hcd);
+	/* The LPM timeout values are pretty host-controller specific, so don't
+	 * enable hub-initiated timeouts unless the vendor has provided
+	 * information about their timeout algorithm.
+	 */
+	if (!xhci || !(xhci->quirks & XHCI_LPM_SUPPORT) ||
+			!xhci->devs[udev->slot_id])
+		return USB3_LPM_DISABLED;
+
+	hub_encoded_timeout = xhci_calculate_lpm_timeout(hcd, udev, state);
+	mel = calculate_max_exit_latency(udev, state, hub_encoded_timeout);
+	if (mel < 0) {
+		/* Max Exit Latency is too big, disable LPM. */
+		hub_encoded_timeout = USB3_LPM_DISABLED;
+		mel = 0;
+	}
+
+	ret = xhci_change_max_exit_latency(xhci, udev, mel);
+	if (ret)
+		return ret;
+	return hub_encoded_timeout;
+}
+
+int xhci_disable_usb3_lpm_timeout(struct usb_hcd *hcd,
+			struct usb_device *udev, enum usb3_link_state state)
+{
+	struct xhci_hcd	*xhci;
+	u16 mel;
+	int ret;
+
+	xhci = hcd_to_xhci(hcd);
+	if (!xhci || !(xhci->quirks & XHCI_LPM_SUPPORT) ||
+			!xhci->devs[udev->slot_id])
+		return 0;
+
+	mel = calculate_max_exit_latency(udev, state, USB3_LPM_DISABLED);
+	ret = xhci_change_max_exit_latency(xhci, udev, mel);
+	if (ret)
+		return ret;
+	return 0;
+}
+/*-------------------------------------------------------------------------*/
+
 int xhci_update_device(struct usb_hcd *hcd, struct usb_device *udev)
 {
 	struct xhci_hcd	*xhci = hcd_to_xhci(hcd);
diff --git a/drivers/usb/host/xhci.h b/drivers/usb/host/xhci.h
index f5cb741..d55b367 100644
--- a/drivers/usb/host/xhci.h
+++ b/drivers/usb/host/xhci.h
@@ -916,6 +916,8 @@ struct xhci_virt_device {
 	u8				real_port;
 	struct xhci_interval_bw_table	*bw_table;
 	struct xhci_tt_bw_info		*tt_info;
+	/* The current max exit latency for the enabled USB3 link states. */
+	u16				current_mel;
 };
 
 /*
@@ -1486,6 +1488,7 @@ struct xhci_hcd {
 #define	XHCI_SW_BW_CHECKING	(1 << 8)
 #define XHCI_AMD_0x96_HOST	(1 << 9)
 #define XHCI_TRUST_TX_LENGTH	(1 << 10)
+#define XHCI_LPM_SUPPORT	(1 << 11)
 	unsigned int		num_active_eps;
 	unsigned int		limit_active_eps;
 	/* There are two roothubs to keep track of bus suspend info for */
@@ -1783,6 +1786,10 @@ void xhci_ring_ep_doorbell(struct xhci_hcd *xhci, unsigned int slot_id,
 /* xHCI roothub code */
 void xhci_set_link_state(struct xhci_hcd *xhci, __le32 __iomem **port_array,
 				int port_id, u32 link_state);
+int xhci_enable_usb3_lpm_timeout(struct usb_hcd *hcd,
+			struct usb_device *udev, enum usb3_link_state state);
+int xhci_disable_usb3_lpm_timeout(struct usb_hcd *hcd,
+			struct usb_device *udev, enum usb3_link_state state);
 void xhci_test_and_clear_bit(struct xhci_hcd *xhci, __le32 __iomem **port_array,
 				int port_id, u32 port_bit);
 int xhci_hub_control(struct usb_hcd *hcd, u16 typeReq, u16 wValue, u16 wIndex,