MIPS: Indicate FP mode in sigcontext sc_used_math

The sc_used_math field of struct sigcontext & its variants has
traditionally been used as a boolean value indicating only whether or
not floating point context is saved within the sigcontext. With various
supported FP modes & the ability to switch between them this information
will no longer be enough to decode the meaning of the data stored in the
sc_fpregs fields of struct sigcontext.

To make that possible 3 bits are defined within sc_used_math:

  - Bit 0 (USED_FP) represents whether FP was used, essentially
    providing the boolean flag which sc_used_math as a whole provided
    previously.

  - Bit 1 (USED_FR1) provides the value of the Status.FR bit at the time
    the FP context was saved.

  - Bit 2 (USED_HYBRID_FPRS) indicates whether the FP context was saved
    under the hybrid FPR scheme. Essentially, when set the odd singles
    are located in bits 63:32 of the preceding even indexed sc_fpregs
    element.

Any userland that tests whether the sc_used_math field is zero or
non-zero will continue to function as expected. Having said that, I
could not find any userland which uses the sc_used_math field at all.

[[email protected]: Fixed rejects.]

Signed-off-by: Paul Burton <[email protected]>
Cc: [email protected]
Cc: Guenter Roeck <[email protected]>
Cc: Matthew Fortune <[email protected]>
Cc: Michael Ellerman <[email protected]>
Cc: [email protected]
Cc: Richard Weinberger <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Maciej W. Rozycki <[email protected]>
Patchwork: https://patchwork.linux-mips.org/patch/10794/
Signed-off-by: Ralf Baechle <[email protected]>

0 files changed, 0 insertions, 0 deletions