Subject: Re: [PATCH 1/3] powerpc: Complete FSCR context switch

From: Anton Blanchard <[email-masked]>
Date: Wed, 13 Apr 2016 20:51:12 +1000

Hi Jack,

> Previously we just saved the FSCR, but only restored it in some
> settings, and never copied it thread to thread. This patch always
> restores the FSCR and formalizes new threads inheriting its setting so
> that later we can manipulate FSCR bits in start_thread.

Will this break the existing FSCR_DSCR bit handling?

         if (cpu_has_feature(CPU_FTR_DSCR)) {
                u64 dscr = get_paca()->dscr_default;
                u64 fscr = old_thread->fscr & ~FSCR_DSCR;

                if (new_thread->dscr_inherit) {
                        dscr = new_thread->dscr;
                        fscr |= FSCR_DSCR;
                }

                if (old_thread->dscr != dscr)
                        mtspr(SPRN_DSCR, dscr);

                if (old_thread->fscr != fscr)
                        mtspr(SPRN_FSCR, fscr);
        }

If not, we should modify the above so we don't write the FSCR twice.

Anton