Uhler, Mike wrote:
Yes. Most 64bit MIPS processors cannot access 64bit content
of registers when it is in 32bit mode.
For clarity, there is no 32/64-bit mode in MIPS processors. There is a
mode in which 64-bit OPERATIONS are enabled (that is, those instructions
which operate on the full width of the registers) - See the definition
of 64-bit Operations Enable in the MIPS64 Architecture for Programmers,
volume III. Note that such operations are always enabled while the
processor is running in Kernel Mode.
The patch is a little short on context, but if you've got a 64-bit
kernel, I had always assumed that save/restore of context is always done
with LD/SD, not by figuring out whether a process has 64-bit operations
enabled, then doing a conditional LD/SD or LW/SW.
This patch for 32bit kernel. We want to save/restore 64bit register
content because the high 32bit of register might be used by multimedia
programs for loongson processor, such as mplayer.
/gmu
---
Michael Uhler, Chief Technology Officer
MIPS Technologies, Inc. Email: uhler AT mips.com
1225 Charleston Road Voice: (650)567-5025 FAX: (650)567-5225
Mountain View, CA 94043
-----Original Message-----
From: linux-mips-bounce@xxxxxxxxxxxxxx
[mailto:linux-mips-bounce@xxxxxxxxxxxxxx] On Behalf Of Fuxin Zhang
Sent: Wednesday, April 18, 2007 6:32 AM
To: Ralf Baechle
Cc: tiansm@xxxxxxxxxx; linux-mips@xxxxxxxxxxxxxx; Fuxin Zhang
Subject: Re: [PATCH 3/16] Kconfig update for lemote fulong mini-PC
+
Is there anything in implementation of this option
Loongson2-specific?
Yes. Most 64bit MIPS processors cannot access 64bit content
of registers when it is in 32bit mode.
Loongson2 has no 32/64 mode bit in fact.
And the usage arise from Loongson2's multimedia extension,
which is also uniq.
If not then I suggest we make this option loook like:
bool "Save 64bit integer registers" if
CPU_SUPPORTS_64BIT_KERNEL &&
32BIT
Somebody else might have a use for it!
Ralf
