Re: [PATCH v2 2/5] riscv: Add checksum library

[Charlie Jenkins]

On Thu, Sep 07, 2023 at 10:52:35AM +0100, Conor Dooley wrote:
> On Tue, Sep 05, 2023 at 09:46:51PM -0700, Charlie Jenkins wrote:
> 
> > +#ifdef CONFIG_RISCV_ISA_ZBB
> > +	if (IS_ENABLED(CONFIG_RISCV_ALTERNATIVE)) {
> > +		/*
> > +		 * Zbb is likely available when the kernel is compiled with Zbb
> > +		 * support, so nop when Zbb is available and jump when Zbb is
> > +		 * not available.
> > +		 */
> > +		asm_volatile_goto(ALTERNATIVE("j %l[no_zbb]", "nop",  0,
> > +					      RISCV_ISA_EXT_ZBB, 1)
> > +		    :
> > +		    :
> > +		    :
> > +		    : no_zbb);
> > +	} else {
> > +		if (!__riscv_isa_extension_available(NULL, RISCV_ISA_EXT_ZBB))
> > +			goto no_zbb;
> > +	}
> 
> Again, do these constructs have an appreciable benefit over doing
> if (!riscv_has_extension_likely(<ZBB>)
> 	goto no_zbb;
> 
> ?
> 
> That encaspulates the fallback to a non-alternative mechanism for you,
> in case you had not noticed.
I got caught up in the other patch where I did not want to fall back, so
then in this patch I forgot I could use riscv_has_extension_likely. I will
make the change.

- Charlie