Messages in this thread | | | Date | Thu, 12 May 2011 09:04:40 +0200 | From | Wolfgang Grandegger <> | Subject | Re: [PATCH v4 1/1] can: add pruss CAN driver. |
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On 05/11/2011 11:31 PM, Arnd Bergmann wrote: > On Tuesday 10 May 2011, Subhasish Ghosh wrote: >> >>>> Yes, In case if we allow the ALL implementation, it hogs the CPU. >>>> In that case we do not need the PRU. The whole purpose of the PRU >>>> is to offload the processor for any such implementations. >>> >>> So the kernel presumably needs to switch between using the PRU and native >>> according to the number of ids being requested at the time ? >> >> All the IDs are programmed into the PRU data RAM. >> The Kernel receives interrupts based upon these IDs. >> I could not clearly follow "PRU and native", could you please elaborate. > > We would really like all CAN drivers to behave the same way. All other > drivers are able to work without filters, so pruss_can should allow that > too, even if it becomes a CPU hog at that time. > > It seems to me that the pruss can implementation has one thing backwards: > it assumes a specific usage model for CAN that it is trying to do offload > for. However, that usage model is currently not even supported by Socket > CAN. If I understand Wolfgang correctly, it is in fact considered an > unwanted limitation of the pruss can driver, instead of a useful feature.
"Unwanted" is not the right word. I see it as a piece of CAN hardware with some serious limitations and I doubt that it will make real CAN users happy. But well, I might be wrong.
> If that interpretation is right, I would seriously recommend rethinking > the design of the CAN firmware for pruss, so you can start doing something > useful with the offload engine that fits into the Socket CAN API, or that > would be a useful extension to Socket CAN that is also implementable in > the kernel for all other drivers in a meaningful way.
It would be really nice if they could provide a better firmware. Anyway, the generic CAN hardware filter interface we spoke about in a previous mail would fit for the PRUSS CAN hardware as well. It just needs to be implemented.
Wolfgang.
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