Subject: Re: [PATCH 2/5] dma-direct: add an explicit dma_direct_get_required_mask

From: Christoph Hellwig <[email-masked]>
Date: Thu, 27 Sep 2018 17:28:18 +0200

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?