From 94dfd7edfd5c9b605caf7b562de7a813d216e011 Mon Sep 17 00:00:00 2001 From: Ming Lei Date: Wed, 3 Jul 2013 22:53:07 +0800 Subject: USB: HCD: support giveback of URB in tasklet context This patch implements the mechanism of giveback of URB in tasklet context, so that hardware interrupt handling time for usb host controller can be saved much, and HCD interrupt handling can be simplified. Motivations: 1), on some arch(such as ARM), DMA mapping/unmapping is a bit time-consuming, for example: when accessing usb mass storage via EHCI on pandaboard, the common length of transfer buffer is 120KB, the time consumed on DMA unmapping may reach hundreds of microseconds; even on A15 based box, the time is still about scores of microseconds 2), on some arch, reading DMA coherent memoery is very time-consuming, the most common example is usb video class driver[1] 3), driver's complete() callback may do much things which is driver specific, so the time is consumed unnecessarily in hardware irq context. 4), running driver's complete() callback in hardware irq context causes that host controller driver has to release its lock in interrupt handler, so reacquiring the lock after return may busy wait a while and increase interrupt handling time. More seriously, releasing the HCD lock makes HCD becoming quite complicated to deal with introduced races. So the patch proposes to run giveback of URB in tasklet context, then time consumed in HCD irq handling doesn't depend on drivers' complete and DMA mapping/unmapping any more, also we can simplify HCD since the HCD lock isn't needed to be released during irq handling. The patch should be reasonable and doable: 1), for drivers, they don't care if the complete() is called in hard irq context or softirq context 2), the biggest change is the situation in which usb_submit_urb() is called in complete() callback, so the introduced tasklet schedule delay might be a con, but it shouldn't be a big deal: - control/bulk asynchronous transfer isn't sensitive to schedule delay - the patch schedules giveback of periodic URBs using tasklet_hi_schedule, so the introduced delay should be very small - for ISOC transfer, generally, drivers submit several URBs concurrently to avoid interrupt delay, so it is OK with the little schedule delay. - for interrupt transfer, generally, drivers only submit one URB at the same time, but interrupt transfer is often used in event report, polling, ... situations, and a little delay should be OK. Considered that HCDs may optimize on submitting URB in complete(), the patch may cause the optimization not working, so introduces one flag to mark if the HCD supports to run giveback URB in tasklet context. When all HCDs are ready, the flag can be removed. [1], http://marc.info/?t=136438111600010&r=1&w=2 Cc: Oliver Neukum Acked-by: Alan Stern Signed-off-by: Ming Lei Signed-off-by: Greg Kroah-Hartman --- include/linux/usb/hcd.h | 17 +++++++++++++++++ 1 file changed, 17 insertions(+) (limited to 'include/linux/usb/hcd.h') diff --git a/include/linux/usb/hcd.h b/include/linux/usb/hcd.h index 1e88377e22f4..a9c7d44bd2ed 100644 --- a/include/linux/usb/hcd.h +++ b/include/linux/usb/hcd.h @@ -22,6 +22,7 @@ #ifdef __KERNEL__ #include +#include #define MAX_TOPO_LEVEL 6 @@ -67,6 +68,13 @@ /*-------------------------------------------------------------------------*/ +struct giveback_urb_bh { + bool running; + spinlock_t lock; + struct list_head head; + struct tasklet_struct bh; +}; + struct usb_hcd { /* @@ -139,6 +147,9 @@ struct usb_hcd { resource_size_t rsrc_len; /* memory/io resource length */ unsigned power_budget; /* in mA, 0 = no limit */ + struct giveback_urb_bh high_prio_bh; + struct giveback_urb_bh low_prio_bh; + /* bandwidth_mutex should be taken before adding or removing * any new bus bandwidth constraints: * 1. Before adding a configuration for a new device. @@ -221,6 +232,7 @@ struct hc_driver { #define HCD_USB25 0x0030 /* Wireless USB 1.0 (USB 2.5)*/ #define HCD_USB3 0x0040 /* USB 3.0 */ #define HCD_MASK 0x0070 +#define HCD_BH 0x0100 /* URB complete in BH context */ /* called to init HCD and root hub */ int (*reset) (struct usb_hcd *hcd); @@ -361,6 +373,11 @@ struct hc_driver { int (*find_raw_port_number)(struct usb_hcd *, int); }; +static inline int hcd_giveback_urb_in_bh(struct usb_hcd *hcd) +{ + return hcd->driver->flags & HCD_BH; +} + extern int usb_hcd_link_urb_to_ep(struct usb_hcd *hcd, struct urb *urb); extern int usb_hcd_check_unlink_urb(struct usb_hcd *hcd, struct urb *urb, int status); -- cgit From 9d8924297cd9c256c23c02abae40202563452453 Mon Sep 17 00:00:00 2001 From: Alan Stern Date: Fri, 30 Aug 2013 10:46:00 -0400 Subject: USB: fix build error when CONFIG_PM_SLEEP isn't enabled This patch fixes a build error that occurs when CONFIG_PM is enabled and CONFIG_PM_SLEEP isn't: >> drivers/usb/host/ohci-pci.c:294:10: error: 'usb_hcd_pci_pm_ops' undeclared here (not in a function) .pm = &usb_hcd_pci_pm_ops Since the usb_hcd_pci_pm_ops structure is defined and used when CONFIG_PM is enabled, its declaration should not be protected by CONFIG_PM_SLEEP. Signed-off-by: Alan Stern Reported-by: kbuild test robot CC: Signed-off-by: Greg Kroah-Hartman --- include/linux/usb/hcd.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'include/linux/usb/hcd.h') diff --git a/include/linux/usb/hcd.h b/include/linux/usb/hcd.h index a9c7d44bd2ed..75efc45eaa2f 100644 --- a/include/linux/usb/hcd.h +++ b/include/linux/usb/hcd.h @@ -428,7 +428,7 @@ extern int usb_hcd_pci_probe(struct pci_dev *dev, extern void usb_hcd_pci_remove(struct pci_dev *dev); extern void usb_hcd_pci_shutdown(struct pci_dev *dev); -#ifdef CONFIG_PM_SLEEP +#ifdef CONFIG_PM extern const struct dev_pm_ops usb_hcd_pci_pm_ops; #endif #endif /* CONFIG_PCI */ -- cgit