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XHCI debug capability (DbC) is an optional but standalone functionality provided by an xHCI host controller. Software learns this capability by walking through the extended capability list of the host. XHCI specification describes DbC in section 7.6. This patch introduces the code to probe and initialize the debug capability hardware during early boot. With hardware initialized, the debug target (system on which this code is running) will present a debug device through the debug port (normally the first USB3 port). The debug device is fully compliant with the USB framework and provides the equivalent of a very high performance (USB3) full-duplex serial link between the debug host and target. The DbC functionality is independent of the xHCI host. There isn't any precondition from the xHCI host side for the DbC to work. One use for this feature is kernel debugging, for example when your machine crashes very early before the regular console code is initialized. Other uses include simpler, lockless logging instead of a full-blown printk console driver and klogd. Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com> Acked-by: Thomas Gleixner <tglx@linutronix.de> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Mathias Nyman <mathias.nyman@linux.intel.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: linux-usb@vger.kernel.org Link: http://lkml.kernel.org/r/1490083293-3792-3-git-send-email-baolu.lu@linux.intel.com [ Small fix to the Kconfig help text. ] Signed-off-by: Ingo Molnar <mingo@kernel.org>
29 lines
789 B
C
29 lines
789 B
C
/*
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* Standalone xHCI debug capability driver
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*
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* Copyright (C) 2016 Intel Corporation
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*
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* Author: Lu Baolu <baolu.lu@linux.intel.com>
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License version 2 as
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* published by the Free Software Foundation.
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*/
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#ifndef __LINUX_XHCI_DBGP_H
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#define __LINUX_XHCI_DBGP_H
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#ifdef CONFIG_EARLY_PRINTK_USB_XDBC
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int __init early_xdbc_parse_parameter(char *s);
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int __init early_xdbc_setup_hardware(void);
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void __init early_xdbc_register_console(void);
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#else
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static inline int __init early_xdbc_setup_hardware(void)
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{
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return -ENODEV;
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}
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static inline void __init early_xdbc_register_console(void)
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{
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}
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#endif /* CONFIG_EARLY_PRINTK_USB_XDBC */
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#endif /* __LINUX_XHCI_DBGP_H */
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