Hi Viresh,
On 26/11/14 08:46, Viresh Kumar wrote:
DT based cpufreq drivers doesn't require much support from platform code now a days as most of the stuff is moved behind generic APIs. Like clk APIs for changing clock rates, regulator APIs for changing voltages, etc.
One of the bottleneck still left was how to select which cpufreq driver to probe for a given platform as there might be multiple drivers available.
Traditionally, we used to create platform devices from machine specific code which binds with a cpufreq driver. And while we moved towards DT based device creation, these devices stayed as is.
The problem is getting worse now as we have architectures now with Zero platform specific code. Forcefully these platforms have to create a new file in drivers/cpufreq/ to just add these platform devices in order to use the generic drivers like cpufreq-dt.c.
This has been discussed again and again, but with no solution yet. Last it was discussed here:
http://lists.infradead.org/pipermail/linux-arm-kernel/2014-May/256154.html
This patch is an attempt towards getting the bindings.
We only need to have one entry in cpus@cpu0 node which will match with drivers name.
This seems fundamentally broken as the driver always needs to unconditionally refer to cpu0. Furthermore the node need not be called cpu0 as the name depends on its reg field.
We can then add another file drivers/cpufreq/device_dt.c, which will add a platform device with the name it finds from cpus@cpu0 node and existing drivers will work without any change. Or something else if somebody have a better proposal. But lets fix the bindings first.
IIUC you will retain the existing list of cpufreq-dt platform device creation as is. If not that breaks compatibility with old DT.
Signed-off-by: Viresh Kumar viresh.kumar@linaro.org
.../devicetree/bindings/cpufreq/drivers.txt | 53 ++++++++++++++++++++++ 1 file changed, 53 insertions(+) create mode 100644 Documentation/devicetree/bindings/cpufreq/drivers.txt
diff --git a/Documentation/devicetree/bindings/cpufreq/drivers.txt b/Documentation/devicetree/bindings/cpufreq/drivers.txt new file mode 100644 index 0000000..bd14917 --- /dev/null +++ b/Documentation/devicetree/bindings/cpufreq/drivers.txt @@ -0,0 +1,53 @@ +Binding to select which cpufreq driver to register
+It is a generic DT binding for selecting which cpufreq-driver to register for +any platform.
+The property listed below must be defined under node /cpus/cpu@0 node. We don't +support multiple CPUFreq driver currently for different cluster and so this +information isn't required to be present in CPUs of all clusters.
+Required properties: +- None
+Optional properties: +- dvfs-method: CPUFreq driver to probe. For example: "arm-bL-cpufreq-dt",
- "cpufreq-dt", etc
You should manage this with compatible rather than a new property as it's not a real hardware property. IMHO Rob's suggestion[1] should work fine.
IIUC, you can have the driver which create this platform device if DT has generic compatible unconditionally(e.g "cpufreq-dt" as you have chosen above). For all existing DT you can create a blacklist of compatibles to match(as it doesn't have the generic compatible) covering all the existing platforms using cpufreq-dt driver, there by you can even remove the platform device creating from multiple places. IMO something like the patch below should work(not tested, also late_initcall is used just to demonstrate the idea)
Rob, please correct me if my understanding is wrong.
Regards, Sudeep
[1] http://lists.infradead.org/pipermail/linux-arm-kernel/2014-May/256191.html
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diff --git a/drivers/cpufreq/cpufreq-dt.c b/drivers/cpufreq/cpufreq-dt.c index f657c571b18e..19a616e298e0 100644 --- a/drivers/cpufreq/cpufreq-dt.c +++ b/drivers/cpufreq/cpufreq-dt.c @@ -387,6 +387,32 @@ static struct platform_driver dt_cpufreq_platdrv = { }; module_platform_driver(dt_cpufreq_platdrv);
+static const struct of_device_id compatible_machine_match[] = { + /* All new machines must have the below compatible to use this driver */ + { .compatible = "cpufreq-generic-dt" }, + /* BLACKLIST of existing users of cpufreq-dt below */ + { .compatible = "samsung,exynos5420" }, + { .compatible = "samsung,exynos5800" }, + {}, +}; + +static int cpufreq_generic_dt_init(void) +{ + struct device_node *root = of_find_node_by_path("/"); + struct platform_device_info devinfo = { .name = "cpufreq-dt", }; + /* + * Initialize the device for the platforms either + * blacklisted or compliant to generic compatible + */ + if (!of_match_node(compatible_machine_match, root)) + return -ENODEV; + + /* Instantiate cpufreq-dt */ + platform_device_register_full(&devinfo); + return 0; +} +late_initcall(cpufreq_generic_dt_init); +