linux-kernel - Re: [PATCH 2/2] PM / clk: Add support for obtaining clocks from device-tree

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Message-ID: <56DD5BE6.1070905@nvidia.com>
Date:	Mon, 7 Mar 2016 10:45:58 +0000
From:	Jon Hunter <jonathanh@...dia.com>
To:	Geert Uytterhoeven <geert@...ux-m68k.org>
CC:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Linux PM list <linux-pm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	<linux-tegra@...r.kernel.org>
Subject: Re: [PATCH 2/2] PM / clk: Add support for obtaining clocks from
 device-tree


On 07/03/16 08:48, Geert Uytterhoeven wrote:
> Hi Jon,
> 
> On Fri, Mar 4, 2016 at 4:33 PM, Jon Hunter <jonathanh@...dia.com> wrote:
>> The PM clocks framework requires clients to pass either a con-id or a
>> valid clk pointer in order to add a clock to a device. Add a new
>> function pm_clk_add_clks_of() to allows device clocks to be retrieved
>> from device-tree and populated for a given device. Note that there
>> should be no need to add a stub function for this new function when
>> CONFIG_OF is not selected because the OF functions used already have
>> stubs functions.
>>
>> In order to handle errors encountered when adding clocks from
>> device-tree, add a function pm_clk_remove_clk() to remove any clocks
>> (using a pointer to the clk structure) that have been added
>> successfully before the error occurred.
>>
>> Signed-off-by: Jon Hunter <jonathanh@...dia.com>
>> ---
>>  drivers/base/power/clock_ops.c | 85 ++++++++++++++++++++++++++++++++++++++++++
>>  include/linux/pm_clock.h       |  9 +++++
>>  2 files changed, 94 insertions(+)
>>
>> diff --git a/drivers/base/power/clock_ops.c b/drivers/base/power/clock_ops.c
>> index 272a52ebafc0..5aa7365699c1 100644
>> --- a/drivers/base/power/clock_ops.c
>> +++ b/drivers/base/power/clock_ops.c
>> @@ -138,6 +138,58 @@ int pm_clk_add_clk(struct device *dev, struct clk *clk)
>>  }
>>
>>  /**
>> + * pm_clk_add_clks_of - Start using device clock(s) for power management.
>> + * @dev: Device whose clock(s) is going to be used for power management.
>> + *
>> + * Add a series of clocks described in the 'clocks' device-tree node for
>> + * a device to the list of clocks used for the power management of @dev.
> 
> This adds all clocks referenced by the device node, while not all clocks may
> be suitable for power management, and some of them may be under explicit
> driver control.
> Cfr. drivers/clk/shmobile/renesas-cpg-mssr.c:cpg_mssr_attach_dev(), which
> looks for module clocks, or core clocks explicitly listed in core_pm_clks[].
> 
> What about adding an optional filter function to filter for suitable clocks?

Yes that sounds reasonable. Are you filtering on clock ID? Would it work
to allow the caller to pass a filter function which takes a struct *clk
as it's only argument?  Or do you prefer we call
of_parse_phandle_with_args(np, "clocks", "#clock-cells", i, &clkspec)
and return the clkspec info?

>> + */
>> +int pm_clk_add_clks_of(struct device *dev)
>> +{
>> +       struct clk **clks;
>> +       unsigned int i, count;
>> +       int ret;
>> +
>> +       if (!dev || !dev->of_node)
>> +               return -EINVAL;
>> +
>> +       count = of_count_phandle_with_args(dev->of_node, "clocks",
>> +                                          "#clock-cells");
>> +       if (count == 0)
>> +               return -ENODEV;
>> +
>> +       clks = kcalloc(count, sizeof(*clks), GFP_KERNEL);
>> +       if (!clks)
>> +               return -ENOMEM;
>> +
> 
> Don't you have to call pm_clk_create() here, to allocate a pm_subsys_data
> structure that pm_clk_add_clk() can populate?

This function will return an error when pm_clk_add_clk() is called if
the user has not called pm_clk_create() first. It seems more natural to
me that the user should call pm_clk_create() before calling
pm_clk_add_clks_of() which is the same convention used for adding clocks
by the other APIs to add clocks.

>> +       for (i = 0; i < count; i++) {
>> +               clks[i] = of_clk_get(dev->of_node, i);
>> +               if (IS_ERR(clks[i])) {
>> +                       ret = PTR_ERR(clks[i]);
>> +                       goto error;
>> +               }
>> +
>> +               ret = pm_clk_add_clk(dev, clks[i]);
>> +               if (ret) {
>> +                       clk_put(clks[i]);
>> +                       goto error;
>> +               }
>> +       }
>> +
>> +       kfree(clks);
>> +
>> +       return 0;
>> +
>> +error:
>> +       while (i--)
>> +               pm_clk_remove_clk(dev, clks[i]);
> 
> Just pm_clk_destroy(dev) to destroy all at once?

Right, however, this will remove all clocks associated with the device
and not just those we have added. It is probably very unlikely that
someone would call pm_clk_add_clks_of() and had previously called
pm_clk_add(), but it seems best to not make any assumptions and only
remove the clocks that were actually added. I guess that it would be
possible to check to see if there were any clocks already added when
this function is called and return an error in that case.

All of that said, I do agree that it may be simpler, if we do call
pm_clk_create() from within pm_clk_add_clks_of() and this would allow us
to pmc_clk_destroy() in the error path. So if this is preferred I could
do that, but I think that I would not allow clocks to be added if
clock_list is not empty when this function is called.

Cheers
Jon