Subject: Re: [PATCH v4 3/3] powerpc/powernv: Parse device tree, population of SPR support

From: Michael Ellerman <[email-masked]>
Date: Tue, 17 Mar 2020 14:13:31 +1100

Pratik Rajesh Sampat <[email-masked]> writes:
> Parse the device tree for nodes self-save, self-restore and populate
> support for the preferred SPRs based what was advertised by the device
> tree.

These should be documented in:
  Documentation/devicetree/bindings/powerpc/opal/power-mgt.txt

> diff --git a/arch/powerpc/platforms/powernv/idle.c b/arch/powerpc/platforms/powernv/idle.c
> index 97aeb45e897b..27dfadf609e8 100644
> --- a/arch/powerpc/platforms/powernv/idle.c
> +++ b/arch/powerpc/platforms/powernv/idle.c
> @@ -1436,6 +1436,85 @@ static void __init pnv_probe_idle_states(void)
>  		supported_cpuidle_states |= pnv_idle_states[i].flags;
>  }
>  
> +/*
> + * Extracts and populates the self save or restore capabilities
> + * passed from the device tree node
> + */
> +static int extract_save_restore_state_dt(struct device_node *np, int type)
> +{
> +	int nr_sprns = 0, i, bitmask_index;
> +	int rc = 0;
> +	u64 *temp_u64;
> +	u64 bit_pos;
> +
> +	nr_sprns = of_property_count_u64_elems(np, "sprn-bitmask");
> +	if (nr_sprns <= 0)
> +		return rc;

Using <= 0 means zero SPRs is treated by success as the caller, is that
intended? If so a comment would be appropriate.

> +	temp_u64 = kcalloc(nr_sprns, sizeof(u64), GFP_KERNEL);
> +	if (of_property_read_u64_array(np, "sprn-bitmask",
> +				       temp_u64, nr_sprns)) {
> +		pr_warn("cpuidle-powernv: failed to find registers in DT\n");
> +		kfree(temp_u64);
> +		return -EINVAL;
> +	}
> +	/*
> +	 * Populate acknowledgment of support for the sprs in the global vector
> +	 * gotten by the registers supplied by the firmware.
> +	 * The registers are in a bitmask, bit index within
> +	 * that specifies the SPR
> +	 */
> +	for (i = 0; i < nr_preferred_sprs; i++) {
> +		bitmask_index = preferred_sprs[i].spr / 64;
> +		bit_pos = preferred_sprs[i].spr % 64;

This is basically a hand coded bitmap, see eg. BIT_WORD(), BIT_MASK() etc.

I don't think there's an easy way to convert temp_u64 into a proper
bitmap, so it's probably not worth doing that. But at least use the macros.

> +		if ((temp_u64[bitmask_index] & (1UL << bit_pos)) == 0) {
> +			if (type == SELF_RESTORE_TYPE)
> +				preferred_sprs[i].supported_mode &=
> +					~SELF_RESTORE_STRICT;
> +			else
> +				preferred_sprs[i].supported_mode &=
> +					~SELF_SAVE_STRICT;
> +			continue;
> +		}
> +		if (type == SELF_RESTORE_TYPE) {
> +			preferred_sprs[i].supported_mode |=
> +				SELF_RESTORE_STRICT;
> +		} else {
> +			preferred_sprs[i].supported_mode |=
> +				SELF_SAVE_STRICT;
> +		}
> +	}
> +
> +	kfree(temp_u64);
> +	return rc;
> +}
> +
> +static int pnv_parse_deepstate_dt(void)
> +{
> +	struct device_node *sr_np, *ss_np;

You never use these concurrently AFAICS, so you could just have a single *np.

> +	int rc = 0, i;
> +
> +	/* Self restore register population */
> +	sr_np = of_find_node_by_path("/ibm,opal/power-mgt/self-restore");

I know the existing idle code uses of_find_node_by_path(), but that's
because it's old and crufty. Please don't add new searches by path. You
should be searching by compatible.

> +	if (!sr_np) {
> +		pr_warn("opal: self restore Node not found");

This warning and the others below will fire on all existing firmware
versions, which is not OK.

> +	} else {
> +		rc = extract_save_restore_state_dt(sr_np, SELF_RESTORE_TYPE);
> +		if (rc != 0)
> +			return rc;
> +	}
> +	/* Self save register population */
> +	ss_np = of_find_node_by_path("/ibm,opal/power-mgt/self-save");
> +	if (!ss_np) {
> +		pr_warn("opal: self save Node not found");
> +		pr_warn("Legacy firmware. Assuming default self-restore support");
> +		for (i = 0; i < nr_preferred_sprs; i++)
> +			preferred_sprs[i].supported_mode &= ~SELF_SAVE_STRICT;
> +	} else {
> +		rc = extract_save_restore_state_dt(ss_np, SELF_SAVE_TYPE);
> +	}
> +	return rc;

You're leaking references on all the device_nodes in here, you need
of_node_put() before exiting.

> +}

cheers