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Message-ID: <20240229132959.GB9179@nvidia.com>
Date: Thu, 29 Feb 2024 09:29:59 -0400
From: Jason Gunthorpe <jgg@...dia.com>
To: Catalin Marinas <catalin.marinas@....com>
Cc: Alexander Gordeev <agordeev@...ux.ibm.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Christian Borntraeger <borntraeger@...ux.ibm.com>,
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Niklas Schnelle <schnelle@...ux.ibm.com>,
Will Deacon <will@...nel.org>
Subject: Re: [PATCH 4/6] arm64/io: Provide a WC friendly __iowriteXX_copy()
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
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