Subject: Re: [PATCH 4/6] arm64/io: Provide a WC friendly __iowriteXX_copy()

From: Jason Gunthorpe <[email-masked]>
Date: Thu, 29 Feb 2024 09:29:59 -0400

On Thu, Feb 29, 2024 at 10:33:04AM +0000, Catalin Marinas wrote:
> On Tue, Feb 20, 2024 at 09:17:08PM -0400, Jason Gunthorpe wrote:
> > +						 const u32 *from, size_t count)
> > +{
> > +	switch (count) {
> > +	case 8:
> > +		asm volatile("str %w0, [%8, #4 * 0]\n"
> > +			     "str %w1, [%8, #4 * 1]\n"
> > +			     "str %w2, [%8, #4 * 2]\n"
> > +			     "str %w3, [%8, #4 * 3]\n"
> > +			     "str %w4, [%8, #4 * 4]\n"
> > +			     "str %w5, [%8, #4 * 5]\n"
> > +			     "str %w6, [%8, #4 * 6]\n"
> > +			     "str %w7, [%8, #4 * 7]\n"
> > +			     :
> > +			     : "rZ"(from[0]), "rZ"(from[1]), "rZ"(from[2]),
> > +			       "rZ"(from[3]), "rZ"(from[4]), "rZ"(from[5]),
> > +			       "rZ"(from[6]), "rZ"(from[7]), "r"(to));
> > +		break;
> 
> BTW, talking of maintenance, would a series of __raw_writel() with
> Mark's recent patch for offset addressing generate similar code? I.e.:

No

gcc intersperses reads/writes (which we were advised not to do) and
clang doesn't support the "o" directive so it produces poor
codegen.

Jason