On Thu, Jun 16, 2011 at 08:30:53PM +0800, Shawn Guo wrote: > Here is the user story that tells the need of the new api. The > mxs-mmc is the mmc host controller for Freescale MXS architecture. > There are a pair of mmc host specific parameters max_seg_size and > max_segs that mxs-mmc host driver needs to tell mmc core, so that > mmc core can know how big each data segment could be and how many > segments could be handled one time in a scatter list by host driver. > > The mxs-mmc driver is one user of dmaengine mxs-dma, and it will call > mxs-dma to transfer data in scatter list. That is to say mxs-mmc has > no idea of what max_seg_size and max_segs should be, because they are > all mxs-dma capability parameters, and mxs-mmc needs to query them > from mxs-dma. This approach would make sense if mxs-mmc were generic, but it's tied to mxs-dma, so it can just as well call mxs-dma to find out how many segments it supports. > Right now, there is well defined dma api (dma_get_max_seg_size) for > mmc to query max_seg_size from dma driver, but the one for max_segs > is missing. That's why mxs-mmc driver has to hard-code it. > > The mxs-mmc is just one example to demonstrate the need of the new > api, and there are other mmc host drivers (mxcmmc on imx-dma is > another example) and possibly even other dmaengine users need this > new api to know the maximum segments that dma driver can handle per > dma call. Again, mxcmmc can just call imx-dma directly. -- Matthew Wilcox Intel Open Source Technology Centre "Bill, look, we understand that you're interested in selling us this operating system, but compare it to ours. We can't possibly take such a retrograde step." -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
