linux-kernel - RE: [PATCH 00/27] sparc32: sunset sun4m and sun4d

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Date: Wed, 20 Dec 2023 09:34:09 +0000
From: David Laight <David.Laight@...LAB.COM>
To: 'Arnd Bergmann' <arnd@...nel.org>, Sam Ravnborg <sam@...nborg.org>, "David
 S . Miller" <davem@...emloft.net>, Andreas Larsson <andreas@...sler.com>
CC: Helge Deller <deller@....de>, Alexander Viro <viro@...iv.linux.org.uk>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Alan Stern
	<stern@...land.harvard.edu>, Jaroslav Kysela <perex@...ex.cz>, Takashi Iwai
	<tiwai@...e.com>, "sparclinux@...r.kernel.org" <sparclinux@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-fbdev@...r.kernel.org" <linux-fbdev@...r.kernel.org>,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
	"linux-sound@...r.kernel.org" <linux-sound@...r.kernel.org>
Subject: RE: [PATCH 00/27] sparc32: sunset sun4m and sun4d

From: Arnd Bergmann
> Sent: 20 December 2023 08:37
> 
> On Tue, Dec 19, 2023, at 22:03, Sam Ravnborg via B4 Relay wrote:
> > TODO before this can be applied:
> > - Ack from davem - as he is the principal sparc maintainer
> > - Tested-by: preferably on a target or QEMU (see above)
> >   I expect bugs as there are some involved changes!
> >
> > Ideas for the future
> > - Apply the most relevant downstream Gaisler patches
> >   - The ones introducing CAS should have preference as we then
> >     can drop the cmpxchg emulation
> 
> One note about the CAS -- as far as I can tell, the absence
> of the futex() syscall on sparc32 kernels means that no glibc
> from the past decade can work correctly as it now requires futex
> for its internal locking, though it does work on sparc64 kernels
> in compat32 mode as well as the LEON3 kernel that adds futex
> support.

Does the glibc mutex 'fast path' also require a CAS instruction?

Presumably having CAS also removes the 'really horrid (tm)' code
required to make all the bitmap operations atomic?

Seems a shame to lose old sparc32 support when (I think) the sun3
in my cupboard would still work - if only it had a working psu.
(The 110/220V switch wasn't connected and the FET wasn't rated
for 450V. UK mains can be 240+10% if you are near a substation.)

	David

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