Re: [PATCH 5/5] MIPS: OCTEON: require the Core-14449 workaround only on CN63XX pass 1

[Thomas Bogendoerfer]

On Tue, Sep 15, 2026 at 07:12:48AM +0000, Orgad Shaneh wrote:
> prom_free_prom_memory() probes the hint field of a compiler-emitted
> PREF and panics when it is not 28, which is what -Wa,-mfix-cn63xxp1
> (CONFIG_CAVIUM_CN63XXP1) rewrites every prefetch in the kernel to. The
> test is gated on OCTEON_IS_MODEL(OCTEON_CN6XXX), so it fires on every
> OCTEON II part, including the pass 2 chips that do not need the
> workaround:
> 
>   Kernel panic - not syncing: OCTEON II DCache prefetch workaround not
>   in place (cfa00004).
>   Please build kernel with proper options (CONFIG_CAVIUM_CN63XXP1).
> 
> on a CN6335-AAP pass 2.2.
> 
> Core-14449 is a CN63XX pass 1.x erratum, and the vendor's own runtime
> check says so: it errors out only for OCTEON_CN63XX_PASS1_X without the
> fix, and otherwise merely warns about lost performance when fixed code
> runs on a part that is not a CN63XX. Narrow the check to CN63XX pass
> 1.x to match.
> 
> The alternative - enabling CONFIG_CAVIUM_CN63XXP1 to satisfy the check -
> is not free: the assembler flag rewrites every prefetch in the kernel
> (77 of them in this build) to pref 0x1c, which is worth avoiding on an
> in-order core whose receive path is dominated by memcpy.
> 
> uasm_i_pref() keeps its OCTEON_CN6XXX condition: it only touches the
> handful of runtime-generated TLB handlers, where the cost does not
> matter.
> 
> Assisted-by: Claude:claude-opus-5
> Signed-off-by: Orgad Shaneh <orgads@xxxxxxxxx>
> ---
> diff --git a/arch/mips/cavium-octeon/setup.c b/arch/mips/cavium-octeon/setup.c
> --- a/arch/mips/cavium-octeon/setup.c
> +++ b/arch/mips/cavium-octeon/setup.c
> @@ -1127,7 +1127,7 @@ EXPORT_SYMBOL(prom_putchar);
>  
>  void __init prom_free_prom_memory(void)
>  {
> -	if (OCTEON_IS_MODEL(OCTEON_CN6XXX)) {
> +	if (OCTEON_IS_MODEL(OCTEON_CN63XX_PASS1_X)) {
>  		/* Check for presence of Core-14449 fix.  */
>  		u32 insn;
>  		u32 *foo;
> -- 
> 2.47.0

applied to mips-next

Thomas.

-- 
Crap can work. Given enough thrust pigs will fly, but it's not necessarily a
good idea.                                                [ RFC1925, 2.3 ]