Messages in this thread | | | Subject | Re: [openib-general] Re: [PATCH 21 of 53] ipath - use phys_to_virt instead of bus_to_virt | From | Roland Dreier <> | Date | Mon, 15 May 2006 16:50:11 -0700 |
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Caitlin> True, but how does that constrain the local interfaces by Caitlin> which the driver is informed of the set of pages that Caitlin> back a given memory region? The driver must still Caitlin> ultimately provide dma accessible addresses to the Caitlin> device. RDMA just changes the timing of the steps, albeit Caitlin> radically, but not what the steps are.
It's only a problem for "reserved L_Key" types of things, where the device is supposed to just use the address given in a work request without translating it. No translation means that work requests have to contain "bus addresses" -- addresses that are what the device would put on the bus to access memory. But if a device needs to simulate DMA in software, then it really needs a kernel virtual address, not a bus address. But it's pretty ugly to have to put that knowledge in every consumer.
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