On Mon, Oct 11, 2010 at 5:22 PM, Wolfgang Denk <[email protected]> wrote: > Dear Reinhard Meyer, > > In message <[email protected]> you wrote: >> >> After thinking alot about this: >> Preface: (for understanding of the issue) > > Thanks!! > >> I see two possible solutions for that problem here: >> 1. generally limit the number of blocks requested to 65535. The performance >> penalty for that is insignificant. (65535 blocks are about 32 MiB) >> 2. limit it on a case by case basis by passing such limit like a host >> capability to the high level part. >> >> Here I would (after much deliberation) favour version 1. > > I agree. Implementing 2) is not worth the effort or the code. 32 MiB > should be enough in most practical cases, and even for really big > transfers it is a more than appropriate chunk size. > >> The second and more serious problem Lei Wen seems to have with his hardware >> is that DMA seems problematic (how so?) for more than 512 KiB. > > Indeed. So far it is totally unclear to me what sort of restriction > this actually is. If my interpretation is correct, than such DMA > transfers should not cross 512 KiB memory boundaries, so the maximum > transfer size is 512 KiB, but only when you start on a 512 KiB > aligned address. Also my interpretation is that this is not actually > a hard restriction, but only a convenience to avoid handling some DMA > interrupt properly - in Linux. I wonder if this really applied to > U-Boot at all, where we use polling instead. > >> I really don't see that we should pull such (unusual?) limitations into the >> high level part. I think the low level driver could issue several DMA >> transfers in that case. > > Again I agree. thi is a low-level, controller specific detail, which > should not affect any upper-layer code. It should be completely hidden > in the controller specific driver code. > >> We need concensus here first before we can issue and comment patches. > > I think both of us agree. We just need to convince Lei Wen...
Ok, I am also fine with not include the 512KiB restriction. So we comes to a conclusion that we still use v1 patch, but cut the 512KiB limitation? Best regards, Lei _______________________________________________ U-Boot mailing list [email protected] http://lists.denx.de/mailman/listinfo/u-boot
