From: Segher Boessenkool <segher@kernel.crashing.org>
To: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Paul Mackerras <paulus@samba.org>,
linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/6] powerpc/time: Rename mftbl() to mftb()
Date: Thu, 1 Oct 2020 15:44:17 -0500 [thread overview]
Message-ID: <20201001204417.GP28786@gate.crashing.org> (raw)
In-Reply-To: <94dc68d3d9ef9eb549796d4b938b6ba0305a049b.1601556145.git.christophe.leroy@csgroup.eu>
On Thu, Oct 01, 2020 at 12:42:39PM +0000, Christophe Leroy wrote:
> On PPC64, we have mftb().
> On PPC32, we have mftbl() and an #define mftb() mftbl().
>
> mftb() and mftbl() are equivalent, their purpose is to read the
> content of SPRN_TRBL, as returned by 'mftb' simplified instruction.
>
> binutils seems to define 'mftbl' instruction as an equivalent
> of 'mftb'.
>
> However in both 32 bits and 64 bits documentation, only 'mftb' is
> defined, and when performing a disassembly with objdump, the displayed
> instruction is 'mftb'
>
> No need to have two ways to do the same thing with different
> names, rename mftbl() to have only mftb().
There are mttbl and mttbu insns (and no mttb insn); they write a 32-bit
half for the time base. There is an mftb, and an mftbu. mftbu reads
the upper half, while mftb reads the *whole* register. SPR 269 is the
TBU register, while SPR 268 is called both TB and TBL. Yes, it is
confusing :-)
The "mftb" name is much clearer than "mftbl" (on 64-bit), because it
reads the whole 64-bit register. On 32-bit mftbl is clearer (but not
defined in the architecture, not officially an insn or even an extended
mnemonic).
Segher
next prev parent reply other threads:[~2020-10-01 20:48 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-01 12:42 [PATCH 1/6] powerpc/time: Rename mftbl() to mftb() Christophe Leroy
2020-10-01 12:42 ` [PATCH 2/6] powerpc/time: Make mftb() common to PPC32 and PPC64 Christophe Leroy
2020-10-01 12:42 ` [PATCH 3/6] powerpc/time: Avoid using get_tbl() and get_tbu() internally Christophe Leroy
2020-10-01 12:42 ` [PATCH 4/6] powerpc/time: Remove get_tbu() Christophe Leroy
2020-10-01 12:42 ` [PATCH 5/6] powerpc/time: Make get_tbl() common to PPC32 and PPC64 Christophe Leroy
2020-10-01 12:42 ` [PATCH 6/6] powerpc/time: Make get_tb() " Christophe Leroy
2020-10-01 20:44 ` Segher Boessenkool [this message]
2020-10-09 6:03 ` [PATCH 1/6] powerpc/time: Rename mftbl() to mftb() Michael Ellerman
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