enhanced reimplemented of the kfifo API
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From: Ira W. Snyder on 15 Jan 2010 17:10 On Fri, Jan 15, 2010 at 10:30:01PM +0100, Stefani Seibold wrote: > > > I'm glad to see this example, it really illustrates how to use the new > > DMA functionality of the kfifo API. > > > > Is there any reason why a very large scatterlist could not be used? I > > have a driver that uses a large scatterlist (~4000 entries, allocated as > > a struct sg_table). I implemented my own copy_from_user() functionality > > into this scatterlist, but I'd love to use the kfifo DMA API instead. > > After filling the scatterlist, I use the usual DMA API's to transfer it > > to my device. > > > > No, but the API will only return max. two entries. > Ah, I see. __kfifo_alloc() uses kmalloc() internally. The kfifo API will not work for my purposes then, since I want to allocate a 16MB chunk of memory, and I'm very uncomfortable doing that with kmalloc(). I'll stick with my custom scatterlist code, which uses alloc_page() to fill in the scatterlist with order-0 allocations. Another nitpick in the code: I've noticed that you use sgl++ in the setup_sgl() function. That should become "sgl = sg_next(sgl);" so that this code can work with an struct sg_table as well. Thanks, Ira -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Ira W. Snyder on 15 Jan 2010 18:40 On Fri, Jan 15, 2010 at 11:05:07PM +0100, Stefani Seibold wrote: > Am Freitag, den 15.01.2010, 14:01 -0800 schrieb Ira W. Snyder: > > On Fri, Jan 15, 2010 at 10:30:01PM +0100, Stefani Seibold wrote: > > > > > > > I'm glad to see this example, it really illustrates how to use the new > > > > DMA functionality of the kfifo API. > > > > > > > > Is there any reason why a very large scatterlist could not be used? I > > > > have a driver that uses a large scatterlist (~4000 entries, allocated as > > > > a struct sg_table). I implemented my own copy_from_user() functionality > > > > into this scatterlist, but I'd love to use the kfifo DMA API instead. > > > > After filling the scatterlist, I use the usual DMA API's to transfer it > > > > to my device. > > > > > > > > > > No, but the API will only return max. two entries. > > > > > > > Ah, I see. __kfifo_alloc() uses kmalloc() internally. The kfifo API will > > not work for my purposes then, since I want to allocate a 16MB chunk of > > memory, and I'm very uncomfortable doing that with kmalloc(). I'll stick > > with my custom scatterlist code, which uses alloc_page() to fill in the > > scatterlist with order-0 allocations. > > > > I think you can use vmalloc() instead and assign this buffer with > kfifo_init(). > Yes, that might be an option. I presume I could still use dma_map_sg() on the resulting scatterlist. > > Another nitpick in the code: I've noticed that you use sgl++ in the > > setup_sgl() function. That should become "sgl = sg_next(sgl);" so that > > this code can work with an struct sg_table as well. > > No, its by definition an array. You cannot pass as struct sg_table to > the kfifo_dma_* functions. > A struct sg_table is a container for an underlying chain of struct scatterlists, allowing for easier allocation. See the definition of struct sg_table and the sgl member (include/linux/scatterlist.h line 11). IIRC, struct sg_table allocates arrays of struct scatterlist in PAGE_SIZE chunks, and chains them together. If you change from "sg++" to "sg_next()", you should be able to work with chained scatterlists. You can only have a single struct page * in one struct scatterlist. This would mean that if I tried to use kfifo_dma_out_prepare() to give me 16MB worth of data, I would need 4096 seperate struct scatterlist entries. One for each struct page * in that 16MB chunk. Jens, you added a lot of the scatterlist chaining code. Can you comment on this? I don't claim to be a scatterlist expert :) Ira -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Stefani Seibold on 16 Jan 2010 02:30
Am Freitag, den 15.01.2010, 15:38 -0800 schrieb Ira W. Snyder: > On Fri, Jan 15, 2010 at 11:05:07PM +0100, Stefani Seibold wrote: > > Am Freitag, den 15.01.2010, 14:01 -0800 schrieb Ira W. Snyder: > > > On Fri, Jan 15, 2010 at 10:30:01PM +0100, Stefani Seibold wrote: > > > > > > > > > I'm glad to see this example, it really illustrates how to use the new > > > > > DMA functionality of the kfifo API. > > > > > > > > > > Is there any reason why a very large scatterlist could not be used? I > > > > > have a driver that uses a large scatterlist (~4000 entries, allocated as > > > > > a struct sg_table). I implemented my own copy_from_user() functionality > > > > > into this scatterlist, but I'd love to use the kfifo DMA API instead. > > > > > After filling the scatterlist, I use the usual DMA API's to transfer it > > > > > to my device. > > > > > > > > > > > > > No, but the API will only return max. two entries. > > > > > > > > > > Ah, I see. __kfifo_alloc() uses kmalloc() internally. The kfifo API will > > > not work for my purposes then, since I want to allocate a 16MB chunk of > > > memory, and I'm very uncomfortable doing that with kmalloc(). I'll stick > > > with my custom scatterlist code, which uses alloc_page() to fill in the > > > scatterlist with order-0 allocations. > > > > > > > I think you can use vmalloc() instead and assign this buffer with > > kfifo_init(). > > > > Yes, that might be an option. I presume I could still use dma_map_sg() > on the resulting scatterlist. > > > > Another nitpick in the code: I've noticed that you use sgl++ in the > > > setup_sgl() function. That should become "sgl = sg_next(sgl);" so that > > > this code can work with an struct sg_table as well. > > > > No, its by definition an array. You cannot pass as struct sg_table to > > the kfifo_dma_* functions. > > > > A struct sg_table is a container for an underlying chain of struct > scatterlists, allowing for easier allocation. See the definition of > struct sg_table and the sgl member (include/linux/scatterlist.h line > 11). > On Fri, Jan 15, 2010 at 11:05:07PM +0100, Stefani Seibold wrote: > > > Am Freitag, den 15.01.2010, 14:01 -0800 schrieb Ira W. Snyder: > > > > > > > Ah, I see. __kfifo_alloc() uses kmalloc() internally. The kfifo API will > > > > not work for my purposes then, since I want to allocate a 16MB chunk of > > > > memory, and I'm very uncomfortable doing that with kmalloc(). I'll stick > > > > with my custom scatterlist code, which uses alloc_page() to fill in the > > > > scatterlist with order-0 allocations. > > > > > > > > > > I think you can use vmalloc() instead and assign this buffer with > > > kfifo_init(). > > > > > > > Yes, that might be an option. I presume I could still use dma_map_sg() > > > IIRC, struct sg_table allocates arrays of struct scatterlist in > PAGE_SIZE chunks, and chains them together. > > If you change from "sg++" to "sg_next()", you should be able to work > with chained scatterlists. You can only have a single struct page * in > one struct scatterlist. This would mean that if I tried to use > kfifo_dma_out_prepare() to give me 16MB worth of data, I would need 4096 > seperate struct scatterlist entries. One for each struct page * in that > 16MB chunk. > No, this would require an initialized scatterlist array and the kfifo_dma_* function does not expect this. And i am not sure why you need 4096 seperate struct scatterlist entries for a continues memory, i need only one. The scatterlist structure contains the page, the offset and the length. The length can be more the a page size. Stefani -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ |