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CONFIG_PROVIDE_OHCI1394_DMA_INIT: Remote debugging over FireWire early on boot

General informations

The Linux kernel configuration item CONFIG_PROVIDE_OHCI1394_DMA_INIT has multiple definitions:

Provide code for enabling DMA over FireWire early on boot found in lib/Kconfig.debug

The configuration item CONFIG_PROVIDE_OHCI1394_DMA_INIT:

Help text

If you want to debug problems which hang or crash the kernel early on boot and the crashing machine has a FireWire port, you can use this feature to remotely access the memory of the crashed machine over FireWire. This employs remote DMA as part of the OHCI1394 specification which is now the standard for FireWire controllers.

With remote DMA, you can monitor the printk buffer remotely using firescope and access all memory below 4GB using fireproxy from gdb. Even controlling a kernel debugger is possible using remote DMA.

Usage:

If ohci1394_dma=early is used as boot parameter, it will initialize all OHCI1394 controllers which are found in the PCI config space.

As all changes to the FireWire bus such as enabling and disabling devices cause a bus reset and thereby disable remote DMA for all devices, be sure to have the cable plugged and FireWire enabled on the debugging host before booting the debug target for debugging.

This code (~1k) is freed after boot. By then, the firewire stack in charge of the OHCI-1394 controllers should be used instead.

See Documentation/debugging-via-ohci1394.txt for more information.

Remote debugging over FireWire early on boot found in lib/Kconfig.debug

The configuration item CONFIG_PROVIDE_OHCI1394_DMA_INIT:

Help text

If you want to debug problems which hang or crash the kernel early on boot and the crashing machine has a FireWire port, you can use this feature to remotely access the memory of the crashed machine over FireWire. This employs remote DMA as part of the OHCI1394 specification which is now the standard for FireWire controllers.

With remote DMA, you can monitor the printk buffer remotely using firescope and access all memory below 4GB using fireproxy from gdb. Even controlling a kernel debugger is possible using remote DMA.

Usage:

If ohci1394_dma=early is used as boot parameter, it will initialize all OHCI1394 controllers which are found in the PCI config space.

As all changes to the FireWire bus such as enabling and disabling devices cause a bus reset and thereby disable remote DMA for all devices, be sure to have the cable plugged and FireWire enabled on the debugging host before booting the debug target for debugging.

This code (~1k) is freed after boot. By then, the firewire stack in charge of the OHCI-1394 controllers should be used instead.

See Documentation/debugging-via-ohci1394.txt for more information.

Hardware

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