Messages in this thread | | | Subject | Re: [PATCH 2/5] dma-direct: add an explicit dma_direct_get_required_mask | From | Robin Murphy <> | Date | Thu, 27 Sep 2018 16:35:21 +0100 |
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On 27/09/18 16:28, Christoph Hellwig wrote: > On Thu, Sep 27, 2018 at 03:12:25PM +0100, Robin Murphy wrote: >>> +u64 dma_direct_get_required_mask(struct device *dev) >>> +{ >>> + u64 max_dma = phys_to_dma_direct(dev, (max_pfn - 1) << PAGE_SHIFT); >>> + >>> + return (1ULL << (fls64(max_dma) - 1)) * 2 - 1; >> >> I think that may as well just use __fls64() - it seems reasonable to assume >> max_dma > 0. Otherwise, > > Is there any good reason to micro-optimize given that this isn't > a fast path?
Not at all, I wasn't even thinking in terms of optimisation other than in terms of number of source characters and levels of parentheses.
But more importantly I was also being a big idiot because no matter how much I have the fls()/__fls() thing in mind, __fls64() doesn't actually exist. Nitpick rescinded!
Robin.
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