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    Subject[ 017/173] ARM: 7566/1: vfp: fix save and restore when running on pre-VFPv3 and CONFIG_VFPv3 set
    3.2-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Paul Walmsley <paul@pwsan.com>

    commit 39141ddfb63a664f26d3f42f64ee386e879b492c upstream.

    After commit 846a136881b8f73c1f74250bf6acfaa309cab1f2 ("ARM: vfp: fix
    saving d16-d31 vfp registers on v6+ kernels"), the OMAP 2430SDP board
    started crashing during boot with omap2plus_defconfig:

    [ 3.875122] mmcblk0: mmc0:e624 SD04G 3.69 GiB
    [ 3.915954] mmcblk0: p1
    [ 4.086639] Internal error: Oops - undefined instruction: 0 [#1] SMP ARM
    [ 4.093719] Modules linked in:
    [ 4.096954] CPU: 0 Not tainted (3.6.0-02232-g759e00b #570)
    [ 4.103149] PC is at vfp_reload_hw+0x1c/0x44
    [ 4.107666] LR is at __und_usr_fault_32+0x0/0x8

    It turns out that the context save/restore fix unmasked a latent bug
    in commit 5aaf254409f8d58229107b59507a8235b715a960 ("ARM: 6203/1: Make
    VFPv3 usable on ARMv6"). When CONFIG_VFPv3 is set, but the kernel is
    booted on a pre-VFPv3 core, the code attempts to save and restore the
    d16-d31 VFP registers. These are only present on non-D16 VFPv3+, so
    this results in an undefined instruction exception. The code didn't
    crash before commit 846a136 because the save and restore code was
    only touching d0-d15, present on all VFP.

    Fix by implementing a request from Russell King to add a new HWCAP
    flag that affirmatively indicates the presence of the d16-d31
    registers:

    http://marc.info/?l=linux-arm-kernel&m=135013547905283&w=2

    and some feedback from MÃ¥ns to clarify the name of the HWCAP flag.

    Signed-off-by: Paul Walmsley <paul@pwsan.com>
    Cc: Tony Lindgren <tony@atomide.com>
    Cc: Catalin Marinas <catalin.marinas@arm.com>
    Cc: Dave Martin <dave.martin@linaro.org>
    Cc: Måns Rullgård <mans.rullgard@linaro.org>
    Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
    [bwh: Backported to 3.2: adjust filename]
    Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
    ---
    --- a/arch/arm/include/asm/vfpmacros.h
    +++ b/arch/arm/include/asm/vfpmacros.h
    @@ -27,9 +27,9 @@
    #if __LINUX_ARM_ARCH__ <= 6
    ldr \tmp, =elf_hwcap @ may not have MVFR regs
    ldr \tmp, [\tmp, #0]
    - tst \tmp, #HWCAP_VFPv3D16
    - ldceql p11, cr0, [\base],#32*4 @ FLDMIAD \base!, {d16-d31}
    - addne \base, \base, #32*4 @ step over unused register space
    + tst \tmp, #HWCAP_VFPD32
    + ldcnel p11, cr0, [\base],#32*4 @ FLDMIAD \base!, {d16-d31}
    + addeq \base, \base, #32*4 @ step over unused register space
    #else
    VFPFMRX \tmp, MVFR0 @ Media and VFP Feature Register 0
    and \tmp, \tmp, #MVFR0_A_SIMD_MASK @ A_SIMD field
    @@ -51,9 +51,9 @@
    #if __LINUX_ARM_ARCH__ <= 6
    ldr \tmp, =elf_hwcap @ may not have MVFR regs
    ldr \tmp, [\tmp, #0]
    - tst \tmp, #HWCAP_VFPv3D16
    - stceql p11, cr0, [\base],#32*4 @ FSTMIAD \base!, {d16-d31}
    - addne \base, \base, #32*4 @ step over unused register space
    + tst \tmp, #HWCAP_VFPD32
    + stcnel p11, cr0, [\base],#32*4 @ FSTMIAD \base!, {d16-d31}
    + addeq \base, \base, #32*4 @ step over unused register space
    #else
    VFPFMRX \tmp, MVFR0 @ Media and VFP Feature Register 0
    and \tmp, \tmp, #MVFR0_A_SIMD_MASK @ A_SIMD field
    --- a/arch/arm/include/asm/hwcap.h
    +++ b/arch/arm/include/asm/hwcap.h
    @@ -18,11 +18,12 @@
    #define HWCAP_THUMBEE (1 << 11)
    #define HWCAP_NEON (1 << 12)
    #define HWCAP_VFPv3 (1 << 13)
    -#define HWCAP_VFPv3D16 (1 << 14)
    +#define HWCAP_VFPv3D16 (1 << 14) /* also set for VFPv4-D16 */
    #define HWCAP_TLS (1 << 15)
    #define HWCAP_VFPv4 (1 << 16)
    #define HWCAP_IDIVA (1 << 17)
    #define HWCAP_IDIVT (1 << 18)
    +#define HWCAP_VFPD32 (1 << 19) /* set if VFP has 32 regs (not 16) */
    #define HWCAP_IDIV (HWCAP_IDIVA | HWCAP_IDIVT)

    #if defined(__KERNEL__) && !defined(__ASSEMBLY__)
    --- a/arch/arm/vfp/vfpmodule.c
    +++ b/arch/arm/vfp/vfpmodule.c
    @@ -610,11 +610,14 @@ static int __init vfp_init(void)
    elf_hwcap |= HWCAP_VFPv3;

    /*
    - * Check for VFPv3 D16. CPUs in this configuration
    - * only have 16 x 64bit registers.
    + * Check for VFPv3 D16 and VFPv4 D16. CPUs in
    + * this configuration only have 16 x 64bit
    + * registers.
    */
    if (((fmrx(MVFR0) & MVFR0_A_SIMD_MASK)) == 1)
    - elf_hwcap |= HWCAP_VFPv3D16;
    + elf_hwcap |= HWCAP_VFPv3D16; /* also v4-D16 */
    + else
    + elf_hwcap |= HWCAP_VFPD32;
    }
    #endif
    /*

    --
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