LoongArch: Detect and expose LAMCAS feature existence

Currently, neither /proc/cpuinfo nor hwcap exposes the existence of the
LAMCAS extension, which is part of LA64v1.1. For example, on a Loongson
3B6000, /proc/cpuinfo is as follows:

        processor               : 23
        package                 : 0
        core                    : 11
        global_id               : 31
        CPU Family              : Loongson-64bit
        Model Name              : Loongson-3B6000
        PRID                    : LA664 (0014d011)
        CPU Revision            : 0x11
        FPU Revision            : 0x01
        CPU MHz                 : 2200.00
        BogoMIPS                : 4400.00
        TLB Entries             : 2112
        Address Sizes           : 48 bits physical, 48 bits virtual
        ISA                     : loongarch32r loongarch32s loongarch64
        Features                : cpucfg lam lam_bh scq ual fpu lsx lasx
        crc32 complex crypto lspw lvz lbt_x86 lbt_arm lbt_mips
        Hardware Watchpoint     : yes, iwatch count: 8, dwatch count: 4

... while the CPUCFG 2 instruction reads "0x7e7ccfcf", whose bit28 is 1,
indicating the actual presence of LAMCAS.

This hinders user-space inspection and detection of LAMCAS. For example,
in SpiderMonkey, we need to switch to larchintrin.h and then use the raw
__cpucfg() to manually perform the bit extraction. Also, a curious user
reading /proc/cpuinfo might be puzzled by the lack of display of LAMCAS.

Expose the existence of LAMCAS via cpuinfo and hwcap. The definition
point of the new LOONGARCH_CPU_LAMCAS flag is chosen so as to match the
practices in commit 1dd3e8a8eeb4059fb34b ("LoongArch: Define instruction
formats for AM{SWAP/ADD}.{B/H} and DBAR").

After this patch, /proc/cpuinfo looks like the following:

        processor               : 23
        package                 : 0
        core                    : 11
        global_id               : 31
        CPU Family              : Loongson-64bit
        Model Name              : Loongson-3B6000
        PRID                    : LA664 (0014d011)
        CPU Revision            : 0x11
        FPU Revision            : 0x01
        CPU MHz                 : 2200.00
        BogoMIPS                : 4400.00
        TLB Entries             : 2112
        Address Sizes           : 48 bits physical, 48 bits virtual
        ISA                     : loongarch32r loongarch32s loongarch64
        Features                : cpucfg lam lam_bh lamcas scq ual fpu lsx
        lasx crc32 complex crypto lspw lvz lbt_x86 lbt_arm lbt_mips
        Hardware Watchpoint     : yes, iwatch count: 8, dwatch count: 4

Note the addition of "lamcas" to the "Features" row.

Signed-off-by: Rong Bao <rong.bao@csmantle.top>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

0 files changed, 0 insertions, 0 deletions