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From: David Laight <David.Laight@ACULAB.COM>
To: 'Arnd Bergmann' <arnd@kernel.org>, Sam Ravnborg <sam@ravnborg.org>, "David
 S . Miller" <davem@davemloft.net>, Andreas Larsson <andreas@gaisler.com>
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	<stern@rowland.harvard.edu>, Jaroslav Kysela <perex@perex.cz>, Takashi Iwai
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Subject: RE: [PATCH 00/27] sparc32: sunset sun4m and sun4d
Thread-Topic: [PATCH 00/27] sparc32: sunset sun4m and sun4d
Thread-Index: AQHaMx+ySWwYagj4Uk6uFCxcDCifEbCx5d1w
Date: Wed, 20 Dec 2023 09:34:09 +0000
Message-ID: <9c4479a3d194450593d541ae02ad288a@AcuMS.aculab.com>
References: <20231219-sam-sparc32-sunset-v3-v1-0-64bb44b598c5@ravnborg.org>
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From: Arnd Bergmann
> Sent: 20 December 2023 08:37
>=20
> 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
>=20
> 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.)

=09David

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