修改led为gpio

hc

2024-10-12 a5969cabbb4660eab42b6ef0412cbbd1200cf14d

 kernel/Documentation/admin-guide/thunderbolt.rst
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-=============
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- Thunderbolt
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-=============
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+.. SPDX-License-Identifier: GPL-2.0
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+
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+======================
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+ USB4 and Thunderbolt
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+======================
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+USB4 is the public specification based on Thunderbolt 3 protocol with
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+some differences at the register level among other things. Connection
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+manager is an entity running on the host router (host controller)
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+responsible for enumerating routers and establishing tunnels. A
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+connection manager can be implemented either in firmware or software.
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+Typically PCs come with a firmware connection manager for Thunderbolt 3
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+and early USB4 capable systems. Apple systems on the other hand use
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+software connection manager and the later USB4 compliant devices follow
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+the suit.
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+
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+The Linux Thunderbolt driver supports both and can detect at runtime which
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+connection manager implementation is to be used. To be on the safe side the
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+software connection manager in Linux also advertises security level
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+``user`` which means PCIe tunneling is disabled by default. The
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+documentation below applies to both implementations with the exception that
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+the software connection manager only supports ``user`` security level and
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+is expected to be accompanied with an IOMMU based DMA protection.
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+
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+Security levels and how to use them
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+-----------------------------------
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 The interface presented here is not meant for end users. Instead there
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 should be a userspace tool that handles all the low-level details, keeps
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 a database of the authorized devices and prompts users for new connections.
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 keep in mind that this bypasses the security levels and makes the system
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 vulnerable to DMA attacks.
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-Security levels and how to use them
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------------------------------------
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 Starting with Intel Falcon Ridge Thunderbolt controller there are 4
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 security levels available. Intel Titan Ridge added one more security level
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 (usbonly). The reason for these is the fact that the connected devices can
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 the device without a key or write a new key and write 1 to the
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 ``authorized`` file to get the new key stored on the device NVM.
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-Upgrading NVM on Thunderbolt device or host
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--------------------------------------------
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+DMA protection utilizing IOMMU
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+------------------------------
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+Recent systems from 2018 and forward with Thunderbolt ports may natively
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+support IOMMU. This means that Thunderbolt security is handled by an IOMMU
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+so connected devices cannot access memory regions outside of what is
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+allocated for them by drivers. When Linux is running on such system it
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+automatically enables IOMMU if not enabled by the user already. These
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+systems can be identified by reading ``1`` from
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+``/sys/bus/thunderbolt/devices/domainX/iommu_dma_protection`` attribute.
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+
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+The driver does not do anything special in this case but because DMA
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+protection is handled by the IOMMU, security levels (if set) are
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+redundant. For this reason some systems ship with security level set to
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+``none``. Other systems have security level set to ``user`` in order to
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+support downgrade to older OS, so users who want to automatically
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+authorize devices when IOMMU DMA protection is enabled can use the
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+following ``udev`` rule::
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+
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+  ACTION=="add", SUBSYSTEM=="thunderbolt", ATTRS{iommu_dma_protection}=="1", ATTR{authorized}=="0", ATTR{authorized}="1"
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+
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+Upgrading NVM on Thunderbolt device, host or retimer
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+----------------------------------------------------
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 Since most of the functionality is handled in firmware running on a
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 host controller or a device, it is important that the firmware can be
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 upgraded to the latest where possible bugs in it have been fixed.
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   `Thunderbolt Updates <https://thunderbolttechnology.net/updates>`_
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-Before you upgrade firmware on a device or host, please make sure it is a
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-suitable upgrade. Failing to do that may render the device (or host) in a
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-state where it cannot be used properly anymore without special tools!
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+Before you upgrade firmware on a device, host or retimer, please make
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+sure it is a suitable upgrade. Failing to do that may render the device
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+in a state where it cannot be used properly anymore without special
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+tools!
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 Host NVM upgrade on Apple Macs is not supported.
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