Messages in this thread | | | Date | Thu, 23 Feb 2006 09:33:48 +0000 | From | Russell King <> | Subject | Re: what's a platform device? |
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On Wed, Feb 22, 2006 at 03:47:40PM -0600, Kumar Gala wrote: > The situation I have is an FPGA connected over PCI. The FPGA implements > various device functionality (serial ports, I2C controller, IR, etc.) as a > single PCI device/function. The FPGA breaks any notion of a true PCI > device, it uses PCI as a device interconnect more than anything else.
We have at least one example where we have a single PCI function containing more than one type of functionality which are the parallel port and serial cards [*]. Normally, the different types of functionality are accessible via different BARs which at least gives some logical separation.
It's not really a good model because you have to have a special PCI probe driver to register the various functionalities with the subsystems rather than using the generic 8250_pci and parport_pci drivers directly. Also it can have problems if you want to have (eg) serial built-in and i2c as a module.
The alternative as Greg points out is to implement a pseudo bus_type, but I start to worry about the overhead associated with doing so.
Given the choice between a small PCI "probe" driver for a small number of functionalities and a complete driver model infrastructure, I'd prefer the former over the latter.
* - I'm slightly biased here because it seems I've ended up "owning" the serial parts of parport_serial, though I don't want to admit that in public. (damn, I just did!) I think that, provided the subsystems are sanely written such that there is very little or no code duplication, this method is as good as any other method.
-- Russell King Linux kernel 2.6 ARM Linux - http://www.arm.linux.org.uk/ maintainer of: 2.6 Serial core - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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