linux-kernel - Re: [PATCH] PM / OPP: Refactor counting of added OPPs for v2 to avoid unsupported OPPs

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Date:   Tue, 21 Aug 2018 22:17:08 -0500
From:   Dave Gerlach <d-gerlach@...com>
To:     Viresh Kumar <viresh.kumar@...aro.org>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>
CC:     <linux-kernel@...r.kernel.org>, <linux-pm@...r.kernel.org>,
        Tony Lindgren <tony@...mide.com>,
        Tero Kristo <t-kristo@...com>, Nishanth Menon <nm@...com>,
        Stephen Boyd <sboyd@...nel.org>, Keerthy J <j-keerthy@...com>
Subject: Re: [PATCH] PM / OPP: Refactor counting of added OPPs for v2 to avoid
 unsupported OPPs

Hi,
On 08/21/2018 10:10 PM, Dave Gerlach wrote:
> Currently the _of_add_opp_table_v2 call loops through the OPP nodes in
> the operating-points-v2 table in the device tree and calls
> _opp_add_static_v2 for each to add them to the table. It counts each
> iteration through this loop as an added OPP, however on platforms making
> use of the opp-supported-hw property, _opp_add_static_v2 does not add
> OPPs that are not seen as supported on the platform but still returns
> success, as this is valid. Because of this the count variable will
> contain the number of OPP nodes in the table in device tree but not
> necessarily the ones that are supported and actually added.
> 
> As this count value is what is checked to determine if there are any
> valid OPPs, if a platform has an operating-points-v2 table with all OPP
> nodes containing opp-supported-hw values that are not currently
> supported then _of_add_opp_table_v2 will fail to abort as it should due
> to an empty table.
> 
> Additionally, since commit 3ba98324e81a ("PM / OPP: Get
> performance state using genpd helper"), the same count variable is
> compared against the number of OPPs containing performance states and
> requires that either all or none have pstates set, however in the case
> of any opp table that has any entries that do not get added by
> _opp_add_static_v2 due to incompatible opp-supported-hw fields, these
> numbers will not match and _of_add_opp_table_v2 will incorrectly fail.
> 
> In order to ensure the count variable reflects the number of OPPs
> actually in the table, increment it during the existing loop which walks
> the opp table to check if pstate is set and then use that for the
> aforementioned checks.
> 
> Fixes: 3ba98324e81a ("PM / OPP: Get performance state using genpd helper")
> Signed-off-by: Dave Gerlach <d-gerlach@...com>
> ---

This is needed to fix cpufreq probe on TI am335x platforms. Seems that
arch/arm/boot/dts/am33xx.dtsi is the only operating-points-v2 table with
multiple opp-supported-hw entries which may not all be supported at once, and
this caused the count differences that led me here.

Regards,
Dave

>  drivers/opp/of.c | 15 ++++++++++-----
>  1 file changed, 10 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/opp/of.c b/drivers/opp/of.c
> index 7af0ddec936b..f288f83a2e62 100644
> --- a/drivers/opp/of.c
> +++ b/drivers/opp/of.c
> @@ -399,8 +399,6 @@ static int _of_add_opp_table_v2(struct device *dev, struct device_node *opp_np)
>  
>  	/* We have opp-table node now, iterate over it and add OPPs */
>  	for_each_available_child_of_node(opp_np, np) {
> -		count++;
> -
>  		ret = _opp_add_static_v2(opp_table, dev, np);
>  		if (ret) {
>  			dev_err(dev, "%s: Failed to add OPP, %d\n", __func__,
> @@ -411,15 +409,22 @@ static int _of_add_opp_table_v2(struct device *dev, struct device_node *opp_np)
>  		}
>  	}
>  
> +	/*
> +	 * Iterate over the list of OPPs that were actually added, as
> +	 * OPPs not supported by the hardware will be ignored by
> +	 * _opp_add_static_v2 above.
> +	 */
> +	list_for_each_entry(opp, &opp_table->opp_list, node) {
> +		count++;
> +		pstate_count += !!opp->pstate;
> +	}
> +
>  	/* There should be one of more OPP defined */
>  	if (WARN_ON(!count)) {
>  		ret = -ENOENT;
>  		goto put_opp_table;
>  	}
>  
> -	list_for_each_entry(opp, &opp_table->opp_list, node)
> -		pstate_count += !!opp->pstate;
> -
>  	/* Either all or none of the nodes shall have performance state set */
>  	if (pstate_count && pstate_count != count) {
>  		dev_err(dev, "Not all nodes have performance state set (%d: %d)\n",
>