linux-kernel - Re: [PATCH 3/3] soc: ti: Add ti_sci_pm

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Date:   Tue, 30 Aug 2016 14:43:22 -0500
From:   Dave Gerlach <d-gerlach@...com>
To:     Ulf Hansson <ulf.hansson@...aro.org>, Nishanth Menon <nm@...com>
CC:     Kevin Hilman <khilman@...nel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Keerthy <j-keerthy@...com>,
        Peter Ujfalusi <peter.ujfalusi@...com>,
        Tero Kristo <t-kristo@...com>,
        Russell King <rmk+kernel@...linux.org.uk>,
        Sudeep Holla <sudeep.holla@....com>,
        Santosh Shilimkar <ssantosh@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        Jon Hunter <jonathanh@...dia.com>
Subject: Re: [PATCH 3/3] soc: ti: Add ti_sci_pm_domains driver

Jon, Ulf,
On 08/26/2016 06:37 PM, Dave Gerlach wrote:
> Hi,
> On 08/25/2016 02:27 AM, Ulf Hansson wrote:
>> + Jon
>>
>> [...]
>>
>>> +
>>> +static int ti_sci_pm_domains_probe(struct platform_device *pdev)
>>> +{
>>> +       struct device *dev = &pdev->dev;
>>> +       struct device_node *np = dev->of_node;
>>> +       struct ti_sci_genpd_data *ti_sci_genpd;
>>> +
>>> +       ti_sci_genpd = devm_kzalloc(dev, sizeof(*ti_sci_genpd), GFP_KERNEL);
>>> +       if (!ti_sci_genpd)
>>> +               return -ENOMEM;
>>> +
>>> +       ti_sci_genpd->ti_sci = devm_ti_sci_get_handle(dev);
>>> +       if (IS_ERR(ti_sci_genpd->ti_sci))
>>> +               return PTR_ERR(ti_sci_genpd->ti_sci);
>>> +
>>> +       ti_sci_genpd->dev = dev;
>>> +
>>> +       INIT_LIST_HEAD(&ti_sci_genpd->pd_list);
>>> +       mutex_init(&ti_sci_genpd->pd_list_mutex);
>>> +
>>> +       return __of_genpd_add_provider(np, of_ti_sci_genpd_xlate_onecell,
>>> +                                      ti_sci_genpd);
>>
>> Jon Hunter are working on adding robust method to be able to remove
>> initialized genpds [1].
>>
>> In that series we intend to remove the __of_genpd_add_provider() API,
>> and instead only have of_genpd_add_provider_onecell() and
>> of_genpd_add_provider_simple(). Could you please convert to use any of
>> these APIs instead?
>
> Thanks for pointing this out. I took at look at the series you've linked and the
> short answer is that I see no good way to directly convert what we've done to
> use those APIs.
>
> On this platform each device has it's power state controlled through the SCI
> protocol described in the cover letter. The system makes a request for powering
> on or off the device using a unique ID number for each device, as provided in
> patches 1 and 2. These operations map to those of a genpd, so we decided to do a
> 1:1 device to genpd mapping, where each device has it's own genpd.
>
> The split that we took from the provided simple and onecell xlate functions
> arises from this mapping. The IDs are not necessarily linear and also they are
> not necessarily defined in a fixed way for all SoCs, they are entirely data
> driven based on the provided device ID. To make use of these IDs, I created a
> new xlate function that takes a onecell value but instead dynamically allocates
> a new genpd, at probe time, to give us a genpd that contains the necessary SoC
> specific data for that device that probed and is mapped directly to the device.
> This lets us only create the genpds we need without having to redefine a static
> list of all possible genpds and duplicate the data.
>
> So my question back would be, how critical is it to be able to drop the ability
> to provide custom xlate functions?

After thinking about this a bit more, I believe I see a way we can use 
the of_genpd_add_provider_onecell, although not optimally. The device 
IDs, and therefore the genpd IDs (in the last email I mentioned we are 
doing a 1:1 device to genpd mapping) are fixed and defined by the 
hardware, and are not linear, there can be gaps and we won't necessarily 
always start at 0 even though we do on this SoC. However, we could build 
an array of genpds that map to our IDs similar to how several have done 
it, like in drivers/soc/bcm/raspberrypi-power.c, but because our IDs can 
have gaps, there will be unused struct generic_pm_domains that get 
allocated and are never touched because the index of the element doesn't 
correspond to a genpd ID.

Based on the ID set provided in patch 2 of this series I see 12 gaps, so 
we'd be wasting space the size of 12 genpds. The ID mapping will change 
on future SoCs, so this number could be larger. Do you think this is an 
acceptable solution? It allows us to play nice with the new genpd 
framework changes at the cost of wasting some space allocated to filler 
genpds.

Regards,
Dave

>
> Regards,
> Dave
>
>>
>> Kind regards
>> Uffe
>>
>> [1]
>> http://www.spinics.net/lists/arm-kernel/msg524151.html
>>
>