Re: [PATCH v2] powerpc/powernv: Cache OPAL check_token() results

[Sourabh Jain <sourabhjain@linux.ibm.com>]

On 26/06/26 18:05, Shivang Upadhyay wrote:
> `opal_check_token()` function is used to determine if a specific
> OPAL firmware call is supported on the current platform. This check
> is performed frequently during boot and runtime, resulting in
> unnecessary firmware calls for the same token values.
>
> Add a caching layer for the opal_check_token() OPAL call to avoid
> repeated firmware calls for token availability checks. This reduces
> firmware call overhead during boot.
>
> Testing with buildroot images shows OPAL calls reduced from
> 35578 to 28983, before console bring-up.

My testing shows similar statistics.

As per my testing, the upstream kernel (without this patch) at commit
840ef6c78e6a2f694b578, compiled with powernv_defconfig, shows ~7K
CHECK_TOKEN OPAL calls to boot the kernel and reach the console.

With this patch included, there are only 8 CHECK_TOKEN opal calls.

There is a significant reduction in CHECK_TOKEN OPAL calls
with this patch. Thanks for working on this improvement.

The changes look good to me. Feel free to add:

Reviewed-by: Sourabh Jain <sourabhjain@linux.ibm.com>

>
> Signed-off-by: Shivang Upadhyay <shivangu@linux.ibm.com>
> ---
> Changelog:
> * v1: https://lore.kernel.org/all/20260601112520.161605-1-shivangu@linux.ibm.com/
>     - implemented tri-state check as suggestd by Sourabh.
>     - made the implementation more clear.
>
> ---
>   arch/powerpc/include/asm/opal.h            |  1 +
>   arch/powerpc/platforms/powernv/opal-call.c |  2 +-
>   arch/powerpc/platforms/powernv/opal.c      | 30 ++++++++++++++++++++++
>   3 files changed, 32 insertions(+), 1 deletion(-)
>
> diff --git a/arch/powerpc/include/asm/opal.h b/arch/powerpc/include/asm/opal.h
> index 0a398265ba04..e7e11479122b 100644
> --- a/arch/powerpc/include/asm/opal.h
> +++ b/arch/powerpc/include/asm/opal.h
> @@ -156,6 +156,7 @@ int64_t opal_pci_next_error(uint64_t phb_id, __be64 *first_frozen_pe,
>   int64_t opal_pci_poll(uint64_t id);
>   int64_t opal_return_cpu(void);
>   int64_t opal_check_token(uint64_t token);
> +int64_t opal_check_token_call(uint64_t token);
>   int64_t opal_reinit_cpus(uint64_t flags);
>   
>   int64_t opal_xscom_read(uint32_t gcid, uint64_t pcb_addr, __be64 *val);
> diff --git a/arch/powerpc/platforms/powernv/opal-call.c b/arch/powerpc/platforms/powernv/opal-call.c
> index 021b0ec29e24..00325c189e69 100644
> --- a/arch/powerpc/platforms/powernv/opal-call.c
> +++ b/arch/powerpc/platforms/powernv/opal-call.c
> @@ -207,7 +207,7 @@ OPAL_CALL(opal_validate_flash,			OPAL_FLASH_VALIDATE);
>   OPAL_CALL(opal_manage_flash,			OPAL_FLASH_MANAGE);
>   OPAL_CALL(opal_update_flash,			OPAL_FLASH_UPDATE);
>   OPAL_CALL(opal_resync_timebase,			OPAL_RESYNC_TIMEBASE);
> -OPAL_CALL(opal_check_token,			OPAL_CHECK_TOKEN);
> +OPAL_CALL(opal_check_token_call,		OPAL_CHECK_TOKEN);
>   OPAL_CALL(opal_dump_init,			OPAL_DUMP_INIT);
>   OPAL_CALL(opal_dump_info,			OPAL_DUMP_INFO);
>   OPAL_CALL(opal_dump_info2,			OPAL_DUMP_INFO2);
> diff --git a/arch/powerpc/platforms/powernv/opal.c b/arch/powerpc/platforms/powernv/opal.c
> index 1946dbdc9fa1..1e9cb5271ee7 100644
> --- a/arch/powerpc/platforms/powernv/opal.c
> +++ b/arch/powerpc/platforms/powernv/opal.c
> @@ -1125,6 +1125,36 @@ EXPORT_SYMBOL_GPL(opal_flash_read);
>   EXPORT_SYMBOL_GPL(opal_flash_write);
>   EXPORT_SYMBOL_GPL(opal_flash_erase);
>   EXPORT_SYMBOL_GPL(opal_prd_msg);
> +
> +/**
> + * opal_check_token - Check if an OPAL call token is supported
> + * @token: OPAL token number to check
> + *
> + * Returns 1 if supported, 0 if not.
> + */
> +int64_t opal_check_token(uint64_t token)
> +{
> +	static u8 token_cache[OPAL_LAST];
> +	enum {
> +		SUPP_UNKNOWN = 0,
> +		PRESENT,
> +		ABSENT
> +	};
> +
> +	if (token > OPAL_LAST)
> +		return 0;
> +
> +	if (token_cache[token] == SUPP_UNKNOWN) {
> +		/* Do the actual opal_call here */
> +		if (opal_check_token_call(token)) {
> +			token_cache[token] = PRESENT;
> +		} else {
> +			token_cache[token] = ABSENT;
> +		}
> +	}
> +
> +	return (token_cache[token] == PRESENT);
> +}
>   EXPORT_SYMBOL_GPL(opal_check_token);
>   
>   /* Convert a region of vmalloc memory to an opal sg list */