On Fri, Jun 19, 2009 at 1:40 PM, Rajat Jain<Rajat.Jain@xxxxxxxxxxxx> wrote: > > Hello Pei / Tom, > > Thanks for the response. Actually I understand why the error is coming, > but my question is a little different. > > I'm saying that I understand that MSI works like following: > > 1) The device is given "an address" and a "value" (using MAR & MDR > registers) that it can use later on to generate an interrupt. > 2) The device later on when wants to send an interrupt, simply write > this "value" into that address using a PCI write transaction. > 3) This "address" and "value" is decided by the Intel APIC architecture > (described in section 9.12 (MSI) of ""Intel 64 and IA-32 Architectures > Software Developer's Manual" > http://www.intel.com/Assets/PDF/manual/253668.pdf). > 4) It is the responsibility of the Intel APIC to generate an interrupt > to the processor when that "value" is written to that "address". > > Now my question is simply this: > > Question > ======== > APIC generates an interrupt when the device writes that "value" into > that "address". But will it also generate an interrupt if a SOFTWARE normally, when a device write to an address, it is a physical address from the device's perspective. > writes that same "value" into the same "address"???? but when a CPU write to an address, due to MMU/pagetable in operation, it is always a virtual address, that have yet to be translated to a physical address. the API ioremap() and friends are used for getting virtual address that will map to the physical address of the hardware device. > > Currently, my software tries the same and gets the APIC error interrupt. > Which is partly justified by the section 9.6.3 (Illegal register access) > since the "address" specified by the same specification (sec 9.12.1) > actually falls into the reserved category. But since the device can use > that address, theoritically my SW should also be able to? No? whether it is the hardware device accessing the DMA memory or software accessing the DMA memory, is the same. yes, should be able to. but u have to make sure that they are touching the same physical address. not sure if ioremap() have been used? sorry if my answer is incorrect......just trying my luck...:-). > > Thanks & Best Regards, > -- Regards, Peter Teoh -- To unsubscribe from this list: send the line "unsubscribe linux-newbie" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.linux-learn.org/faqs
