Messages in this thread | | | From | David Brownell <> | Subject | Re: [spi-devel-general] SPI bus driver synchronous support | Date | Thu, 30 Mar 2006 09:53:00 -0800 |
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On Wednesday 29 March 2006 11:49 am, Kumar Gala wrote:
> The case I have is I need to talk to a microcontroller connected over > SPI. I'd like to be able to issue a command to the microcontroller > in a MachineCheck handler before the system reboots.
Issuing the command is trivial, but knowing it completes before the MCE handler completes is an entirely different kettle of fish. Remember, the SPI controller may in general be busy with some other request, which would need to finish first even if some other request _could_ jump to the head of the request queue.
I suspect some system designer is thinking about the problem wrong if you believe you need that kind of solution. If for some reason your board design requires that sort of access, then what you'd be needing is a way to abort then bypass the normal SPI stack. It could work like any other board-specific hack.
> I need a truly > synchronous interface opposed to one fronting the async interface.
I think the word "synchronous" means something other than what you're implying here. Normally in Linux, it means that the request handling blocks until completion, sleeping allowed.
You seem to be thinking about something behaving more like a register access, which is safe to call when in_irq().
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