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SubjectBlocking access to a PCI device for "a long time"?
Some of you may have followed the earlier discussions on the open 
graphics card. One problem is that we are trying to fit a lot of logic
into a small area, so one thing we're considering is having multiple
FPGA bitfiles in the PROM. When changing modes (ie. from VGA to 3D),
the driver would instruct the FPGA to reload itself from a different
part of the bitfile PROM.

The issue here is that it's a complete reload of the FPGA which makes it
completely lose all configuration state, which includes PCI config.
Thus, the process for switching modes would go something like this:

- Make sure that nothing can get confused by the device "going away" on
the PCI/AGP bus, using whatever kernel locks are necessary
- Save PCI config state of device
- Instruct the FPGA to reload itself
- Wait many, many, many, many milliseconds
- Reload PCI config state
- Unlock and continue

Other drivers accessing the bus for other devices is PROBABLY not a
problem, but nothing can touch the GPU while it's reloading.

Are there any problems with this approach that would make it a really
bad idea?
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