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>

1 files changed, 7 insertions, 0 deletions

diff --git a/drivers/usb/host/xhci.h b/drivers/usb/host/xhci.h
index f5cb7417f231..d55b3678c8b8 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,