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

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Message-Id: <ec342c73-1e10-4e63-627d-01eaa2bd8593@linux.ibm.com>
Date:   Tue, 17 Mar 2020 19:38:53 +0530
From:   Pratik Sampat <psampat@...ux.ibm.com>
To:     Michael Ellerman <mpe@...erman.id.au>,
        linux-kernel@...r.kernel.org, linuxppc-dev@...abs.org,
        svaidy@...ux.ibm.com, ego@...ux.vnet.ibm.com, linuxram@...ibm.com,
        pratik.sampat@...ibm.com, pratik.r.sampat@...il.com
Subject: Re: [PATCH v4 3/3] powerpc/powernv: Parse device tree, population of
 SPR support

Thank you Michael for the review.


On 17/03/20 8:43 am, Michael Ellerman wrote:
> Pratik Rajesh Sampat <psampat@...ux.ibm.com> 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

Sure thing I'll add them.

>> 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.

My bad, this is undesirable. This should be treated as a failure.
I'll fix this.

>> +	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.

Right. I'll use the macros for a cleaner abstraction.

>> +		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.

Sure, got rid of it.

>> +	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.
>
Alright, I'll replace of_find_node_by_path() calls with of_find_compatible_node()

>> +	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.

I'll get rid of the warnings. They seem unnecessary to me also now.

>> +	} 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.

Got it. I'll clear the refcount before exitting.

>> +}
>
> cheers
Thanks!
Pratik