Messages in this thread | | | From | Eric Miao <> | Date | Mon, 16 Aug 2010 20:14:27 +0800 | Subject | Re: [PATCH] [MTD] [NAND] pxa3xx: fix ns2cycle equation |
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On Mon, Aug 16, 2010 at 6:32 PM, David Woodhouse <dwmw2@infradead.org> wrote: > On Mon, 2010-08-16 at 16:09 +0800, Axel Lin wrote: >> Test on a PXA310 platform with Samsung K9F2G08X0B NAND flash, >> with tCH=5 and clk is 156MHz, ns2cycle(5, 156000000) returns -1. >> >> ns2cycle returns negtive value will break NDTR0_tXX macros. >> >> After checking the commit log, I found the problem is introduced by >> commit 5b0d4d7c8a67c5ba3d35e6ceb0c5530cc6846db7 >> "[MTD] [NAND] pxa3xx: convert from ns to clock ticks more accurately" >> >> To get num of clock cycles, we use below equation: >> num of clock cycles = time (ns) / one clock cycle (ns) + 1 >> We need to add 1 cycle here because integer division will truncate the result. >> It is possible the developers set the Min values in SPEC for timing settings. >> Thus the truncate may cause problem, and it is safe to add an extra cycle here. >> >> The various fields in NDTR{01} are in units of clock ticks minus one, >> thus we should subtract 1 cycle then. >> >> Thus the correct equation should be: >> num of clock cycles = time (ns) / one clock cycle (ns) + 1 - 1 >> = time (ns) / one clock cycle (ns) > > Looks sane to me; thanks. Wants to go to stable@ too, yes? > > Can I have an Acked-By: from Matt and/or Eric? >
Acked-by: Eric Miao <eric.y.miao@gmail.com> -- 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/
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