Messages in this thread | | | From | Masahiro Yamada <> | Date | Fri, 10 Mar 2017 20:00:03 +0900 | Subject | Re: [PATCH 00/39] mtd: nand: denali: 2nd round of Denali NAND IP patch bomb |
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Hi Boris,
I am almost getting v2 done, and now I am testing it.
I am having one problem. Please teach me.
2016-11-30 17:17 GMT+09:00 Boris Brezillon <boris.brezillon@free-electrons.com>: >> [2] >> Remove driver-internal bounce buffer. >> The current Denali driver allocate DMA_BIDIRECTIONAL buffer >> to use it as a driver-internal bounce buffer. >> >> The hardware transfer page data into the bounce buffer, >> then CPU copies from the bounce buffer to a given buf (and oob_poi). >> This is not efficient. >> >> So, I want to set NAND_USE_BOUNCE_BUFFER flag >> and do dma_map_single directly for a given buffer. > > Sounds good. Be careful though, when you use the generic bounce buffer > interface you might have to clear the page cache info (->pagebuf = -1).
Instead of memcpy() of the whole page, I am trying to use dma_map_single() in ecc->read_page() / ecc->write_page(). This will allow direct transfer between the buffer and the device by DMA.
But, this does not work for Denali if use_bufpoi is set in nand_do_read_ops().
In the following code in nand_scan_tail(),
if (!(chip->options & NAND_OWN_BUFFERS)) { nbuf = kzalloc(sizeof(*nbuf) + mtd->writesize + mtd->oobsize * 3, GFP_KERNEL); if (!nbuf) return -ENOMEM; nbuf->ecccalc = (uint8_t *)(nbuf + 1); nbuf->ecccode = nbuf->ecccalc + mtd->oobsize; nbuf->databuf = nbuf->ecccode + mtd->oobsize;
chip->buffers = nbuf;
chip->buffers->databuf has no guarantee for DMA'able alignment. (actually it has unwanted offset 0xc because sizeof(*nbuf) == 0xc on 32bit systems)
If we could change the code as follows,
nbuf->ecccalc = kmalloc(mtd->oobsize, GFP_KERNEL); nbuf->ecccode = kmalloc(mtd->oobsize, GFP_KERNEL); nbuf->databuf = kmalloc(mtd->writesize + mtd->oobsize, GFP_KERNEL);
chip->buffers->databuf would have DMA'able alignment in most cases without NAND_OWN_BUFFERS. (but, I am not sure if this is a good idea)
So, the idea of NAND_OWN_BUFFERS is that drivers should allocate own buffers if they need to perform DMA-mapping in read_page(), write_page(), right?
However, "git grep NAND_OWN_BUFFERS" shows cafe_nand.c is the only driver that does so.
On the other hand, "git grep dma_map_single" has more hits, i.e. some drivers perform dma_map_single() for read/write without NAND_OWN_BUFFERS.
I have no idea how they are working.
-- Best Regards Masahiro Yamada
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