Re: [RFC PATCH 06/10] powerpc/powernv: opal use new opal call entry point if it exists

[Gautham R Shenoy <ego@linux.vnet.ibm.com>]

Hello Nicholas,

On Sat, May 02, 2020 at 09:19:10PM +1000, Nicholas Piggin wrote:
> OPAL may advertise new endian-specific entry point which has different
> calling conventions including using the caller's stack, but otherwise
> provides the standard OPAL call API without any changes required to
> the OS.
> 
> Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
> ---

[..snip..]

> index 506b1798081a..32857254d268 100644
> --- a/arch/powerpc/platforms/powernv/opal-call.c
> +++ b/arch/powerpc/platforms/powernv/opal-call.c
> @@ -92,6 +92,18 @@ static s64 __opal_call_trace(s64 a0, s64 a1, s64 a2, s64 a3,
>  #define DO_TRACE false
>  #endif /* CONFIG_TRACEPOINTS */
> 
> +struct opal {
> +	u64 base;
> +	u64 entry;
> +	u64 size;
> +	u64 v4_le_entry;
> +};
> +extern struct opal opal;
> +
> +typedef int64_t (*opal_v4_le_entry_fn)(uint64_t r3, uint64_t r4, uint64_t r5,
> +                               uint64_t r6, uint64_t r7, uint64_t r8,
> +                               uint64_t r9, uint64_t r10);
> +
>  static int64_t opal_call(int64_t a0, int64_t a1, int64_t a2, int64_t a3,
>  	     int64_t a4, int64_t a5, int64_t a6, int64_t a7, int64_t opcode)
>  {
> @@ -99,6 +111,30 @@ static int64_t opal_call(int64_t a0, int64_t a1, int64_t a2, int64_t a3,
>  	unsigned long msr = mfmsr();
>  	bool mmu = (msr & (MSR_IR|MSR_DR));
>  	int64_t ret;
> +	opal_v4_le_entry_fn fn;

fn should be initialized to NULL here to ensure correctness when
kernel is built with CONFIG_CPU_BIG_ENDIAN.

> +
> +	if (IS_ENABLED(CONFIG_CPU_LITTLE_ENDIAN))
> +		fn = (opal_v4_le_entry_fn)(opal.v4_le_entry);
> +
> +	if (fn) {
> +		if (!mmu) {
> +			BUG_ON(msr & MSR_EE);
> +			ret = fn(opcode, a0, a1, a2, a3, a4, a5, a6);
> +			return ret;
> +		}
> +
> +		local_irq_save(flags);
> +		hard_irq_disable(); /* XXX r13 */
> +		msr &= ~MSR_EE;
> +		mtmsr(msr & ~(MSR_IR|MSR_DR));
> +
> +		ret = fn(opcode, a0, a1, a2, a3, a4, a5, a6);
> +
> +		mtmsr(msr);
> +		local_irq_restore(flags);
> +
> +		return ret;
> +	}
> 
>  	msr &= ~MSR_EE;
> 

--
Thanks and Regards
gautham.