linux-kernel - Re: [PATCH v3 2/3] opp/of: Allow empty opp-table with opp-shared

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Message-ID: <20201103050141.kiuyotzt4brisch7@vireshk-i7>
Date:   Tue, 3 Nov 2020 10:31:41 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Nicola Mazzucato <nicola.mazzucato@....com>
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-pm@...r.kernel.org, devicetree@...r.kernel.org,
        sudeep.holla@....com, rjw@...ysocki.net, vireshk@...nel.org,
        robh+dt@...nel.org, sboyd@...nel.org, nm@...com,
        daniel.lezcano@...aro.org, morten.rasmussen@....com,
        chris.redpath@....com
Subject: Re: [PATCH v3 2/3] opp/of: Allow empty opp-table with opp-shared

On 02-11-20, 12:01, Nicola Mazzucato wrote:
> The opp binding now allows to have an empty opp table and shared-opp to
> merely describe a hw connection among devices (f/v lines).
> 
> When initialising an opp table, allow such case by:
> - treating some errors as warnings
> - do not mark empty tables as shared
> - don't fail on empty table
> 
> Signed-off-by: Nicola Mazzucato <nicola.mazzucato@....com>
> ---
>  drivers/opp/of.c | 13 +++++++++++--
>  1 file changed, 11 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/opp/of.c b/drivers/opp/of.c
> index 874b58756220..b0230490bb31 100644
> --- a/drivers/opp/of.c
> +++ b/drivers/opp/of.c
> @@ -157,6 +157,11 @@ static void _opp_table_free_required_tables(struct opp_table *opp_table)
>  /*
>   * Populate all devices and opp tables which are part of "required-opps" list.
>   * Checking only the first OPP node should be enough.
> + *
> + * Corner case: empty opp table and opp-shared found. In this case we set
> + * unconditionally the opp table access to exclusive, as the opp-shared property
> + * is used purely to describe hw connections. Such information will be retrieved
> + * via dev_pm_opp_of_get_sharing_cpus().
>   */
>  static void _opp_table_alloc_required_tables(struct opp_table *opp_table,
>  					     struct device *dev,
> @@ -169,7 +174,9 @@ static void _opp_table_alloc_required_tables(struct opp_table *opp_table,
>  	/* Traversing the first OPP node is all we need */
>  	np = of_get_next_available_child(opp_np, NULL);
>  	if (!np) {
> -		dev_err(dev, "Empty OPP table\n");
> +		dev_warn(dev, "Empty OPP table\n");
> +
> +		opp_table->shared_opp = OPP_TABLE_ACCESS_EXCLUSIVE;

I am not sure I understand the reasoning behind this.

>  		return;
>  	}
>  
> @@ -377,7 +384,9 @@ int dev_pm_opp_of_find_icc_paths(struct device *dev,
>  	struct icc_path **paths;
>  
>  	ret = _bandwidth_supported(dev, opp_table);
> -	if (ret <= 0)
> +	if (ret == -EINVAL)
> +		return 0; /* Empty OPP table is a valid corner-case, let's not fail */
> +	else if (ret <= 0)
>  		return ret;
>  
>  	ret = 0;
> -- 
> 2.27.0

-- 
viresh