Re: [PATCH] riscv: fixup max_low_pfn with PFN_DOWN.

[Palmer Dabbelt]

On Tue, 15 Jan 2019 17:07:38 PST (-0800), guoren@xxxxxxxxxx wrote:
> Hi Christoph,
>
> I use PFN_DOWN() every where as possible and seems it's a habit
> problem. So let risc-v maintainer to choose "PFN_DOW()" or
> ">> PAGE_SHIFT".
>
> Also the same with "end_of_DRAM & max_low_pfn".

PFN_DOWN makes sense to me, as that's what we're trying to do here (round a 
physical address down to page frame number).  Am a I misunderstanding 
something?

> Best Regards
>  Guo Ren
>
> On Tue, Jan 15, 2019 at 08:12:54AM -0800, Christoph Hellwig wrote:
> > On Wed, Jan 16, 2019 at 12:10:00AM +0800, Guo Ren wrote:
> > > > >  	set_max_mapnr(PFN_DOWN(mem_size));
> > > > > -	max_low_pfn = memblock_end_of_DRAM();
> > > > > +	max_low_pfn = PFN_DOWN(memblock_end_of_DRAM());
> > > >
> > > > I know it is used just above, but can we please just switch this
> > > > code to use >> PAGE_SHIFT instead of PFN_DOWN, which just horribly
> > > > obsfucates what is going on?
> > > ???
> > > #define PFN_DOWN(x)	((x) >> PAGE_SHIFT)
> > >
> > > phys_addr_t __init_memblock memblock_end_of_DRAM(void)
> > > {
> > > 	int idx = memblock.memory.cnt - 1;
> > >
> > > 	return (memblock.memory.regions[idx].base + memblock.memory.regions[idx].size);
> > > }
> > >
> > > What's the problem? PFN_DOWN() couldn't be used with function call?
> >
> > PFN_DOWN gives you the correct result.  But I think it actually
> > drastically reduces readability over just opencoding it.
> >
> > > My patch just want to point out that max_low_pfn is PFN not size. In fact
> > > there is no error for running without my patch :P
> >
> > No, I think your patch is correct.  I just wonder if we could make
> > the code easier to read.