Messages in this thread | | | Date | Tue, 31 Dec 2002 15:23:43 -0800 | From | David Brownell <> | Subject | Re: [PATCH] generic device DMA (dma_pool update) |
| |
>> Such a facility could be layered on top of your interface >>perhaps by extending the mempool code to pass an extra parameter >>around. If so, then you should think about arranging your interface >>so that it could be driven with as little glue as possible by mempool. >> > > > What is that parameter? The size, I assume. To do that you'd > need to create different pools for different allocation sizes.
In the other allocators it'd be the dma_addr_t for the memory being returned ...
I don't think the mempool stuff needs that, see the fragments below.
> Bear in mind that mempool only makes sense with memory objects > which have the special characteristic that "if you wait long enough, > someone will free one". ie: BIOs, nfs requests, etc. Probably, > DMA buffers fit into that picture as well.Inside the USB host controller drivers I think that mostly applies to transfer descriptors (tds), which are freed when some other request completes. An 8K buffer takes 1 (ehci), 2 (ohci) or 128 (uhci) of those, and as you know scatterlists can queue quite a few pages.
I'd imagine mempool based td allocation might go like this; it should be easy enough to slip into most of the HCDs:
void *mempool_alloc_td (int mem_flags, void *pool) { struct td *td; dma_addr_t dma;
td = dma_pool_alloc (pool, mem_flags, &dma); if (!td) return td; td->td_dma = dma; /* feed to the hardware */ ... plus other init return td; }
void mempool_free_td (void *_td, void *pool) { struct td *td = _td;
dma_pool_free (pool, td, td->dma); }
USB device drivers tend to either allocate and reuse one dma buffer (kmalloc/kfree usage pattern) or use dma mapping ... so far.
- Dave
- 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/
| |