mirror of
https://github.com/torvalds/linux.git
synced 2024-12-28 13:51:44 +00:00
1ea7e0e8e3
There are various functions within the USB core that will need to disable USB 3.0 link power states. For example, when a USB device driver is being bound to an interface, we need to disable USB 3.0 LPM until we know if the driver will allow hub-initiated LPM transitions. Another example is when the USB core is switching alternate interface settings. The USB 3.0 timeout values are dependent on what endpoints are enabled, so we want to ensure that LPM is disabled until the new alt setting is fully installed. Multiple functions need to disable LPM, and those functions can even be nested. For example, usb_bind_interface() could disable LPM, and then call into the driver probe function, which may attempt to switch to a different alt setting. Therefore, we need to keep a count of the number of functions that require LPM to be disabled at any point in time. Introduce two new USB core API calls, usb_disable_lpm() and usb_enable_lpm(). These functions increment and decrement a new variable in the usb_device, lpm_disable_count. If usb_disable_lpm() fails, it will call usb_enable_lpm() in order to balance the lpm_disable_count. These two new functions must be called with the bandwidth_mutex locked. If the bandwidth_mutex is not already held by the caller, it should instead call usb_unlocked_disable_lpm() and usb_enable_lpm(), which take the bandwidth_mutex before calling usb_disable_lpm() and usb_enable_lpm(), respectively. Introduce a new variable (timeout) in the usb3_lpm_params structure to keep track of the currently enabled U1/U2 timeout values. When usb_disable_lpm() is called, and the USB device has the U1 or U2 timeouts set to a non-zero value (meaning either device-initiated or hub-initiated LPM is enabled), attempt to disable LPM, regardless of the state of the lpm_disable_count. We want to ensure that all callers can be guaranteed that LPM is disabled if usb_disable_lpm() returns zero. Otherwise the following scenario could occur: 1. Driver A is being bound to interface 1. usb_probe_interface() disables LPM. Driver A doesn't care if hub-initiated LPM is enabled, so even though usb_disable_lpm() fails, the probe of the driver continues, and the bandwidth mutex is dropped. 2. Meanwhile, Driver B is being bound to interface 2. usb_probe_interface() grabs the bandwidth mutex and calls usb_disable_lpm(). That call should attempt to disable LPM, even though the lpm_disable_count is set to 1 by Driver A. For usb_enable_lpm(), we attempt to enable LPM only when the lpm_disable_count is zero. If some step in enabling LPM fails, it will only have a minimal impact on power consumption, and all USB device drivers should still work properly. Therefore don't bother to return any error codes. Don't enable device-initiated LPM if the device is unconfigured. The USB device will only accept the U1/U2_ENABLE control transfers in the configured state. Do enable hub-initiated LPM in that case, since devices are allowed to accept the LGO_Ux link commands in any state. Don't enable or disable LPM if the device is marked as not being LPM capable. This can happen if: - the USB device doesn't have a SS BOS descriptor, - the device's parent hub has a zeroed bHeaderDecodeLatency value, or - the xHCI host doesn't support LPM. Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com> Cc: Andiry Xu <andiry.xu@amd.com> Cc: Alan Stern <stern@rowland.harvard.edu> Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com> |
||
|---|---|---|
| .. | ||
| acpi | ||
| asm-generic | ||
| crypto | ||
| drm | ||
| keys | ||
| linux | ||
| math-emu | ||
| media | ||
| misc | ||
| mtd | ||
| net | ||
| pcmcia | ||
| rdma | ||
| rxrpc | ||
| scsi | ||
| sound | ||
| target | ||
| trace | ||
| video | ||
| xen | ||
| Kbuild | ||