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

[Pratik Sampat]

Thank you Michael for the review.


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