linux-kernel - Re: [RFC/PATCH 0/3] ARM: Use udiv/sdiv for __aeabi

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Date:	Sun, 22 Nov 2015 00:14:14 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Måns Rullgård <mans@...sr.com>
Cc:	linux-arm-kernel@...ts.infradead.org,
	Stephen Boyd <sboyd@...eaurora.org>,
	linux-arm-msm@...r.kernel.org,
	Steven Rostedt <rostedt@...dmis.org>,
	linux-kernel@...r.kernel.org, Nicolas Pitre <nico@...xnic.net>
Subject: Re: [RFC/PATCH 0/3] ARM: Use udiv/sdiv for __aeabi_{u}idiv library functions

On Saturday 21 November 2015 22:11:36 Måns Rullgård wrote:
> Arnd Bergmann <arnd@...db.de> writes:
> > On Saturday 21 November 2015 20:45:38 Måns Rullgård wrote:
> >> On 21 November 2015 20:39:58 GMT+00:00, Arnd Bergmann <arnd@...db.de> wrote:
> >> 
> >> The ARM ARM says anything with virt has idiv, lpae doesn't matter.
> >
> > Ok, and anything with virt also has lpae by definition. The question is
> > whether we care about using idiv on cores that do not have lpae, or that
> > have neither lpae nor virt.
> 
> The question is, are there any such cores?  GCC doesn't know of any, but
> then it's missing most non-ARM designs.

Exactly. Stephen should be able to find out about the Qualcomm cores,
and http://comments.gmane.org/gmane.linux.ports.arm.kernel/426289 has
some information about the others:
 * Brahma-B15 supports all three.
 * Dove (PJ4) reports idiv only in thumb mode, which I'm tempted to ignore
   for the kernel, as it supports neither lpae nor idiva.
 * Armada 370/XP (PJ4B) reports support for idiva and idivt, but according to
   https://groups.google.com/a/dartlang.org/forum/#!topic/reviews/9wvsJvq0YYY
   that may be a lie.
 * According to the same source, Krait fails to report idiva and idivt,
   but supports both anyway. However, I found reports on the web where
   /proc/cpuinfo correctly contains the flags on the same SoC (APQ8064)
   that was mentioned there, so maybe they were just running an old
   kernel.

	Arnd
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