Subject: Re: [PATCH 4/4] cpufreq: add driver for Raspbery Pi

From: Eric Anholt <[email-masked]>
Date: Tue, 04 Jun 2019 17:18:54 -0700

Nicolas Saenz Julienne <[email-masked]> writes:

> Raspberry Pi's firmware offers and interface though which update it's
> performance requirements. It allows us to request for specific runtime
> frequencies, which the firmware might or might not respect, depending on
> the firmware configuration and thermals.
>
> As the maximum and minimum frequencies are configurable in the firmware
> there is no way to know in advance their values. So the Raspberry Pi
> cpufreq driver queries them, builds an opp frequency table to then
> launch cpufreq-dt.
>
> Signed-off-by: Nicolas Saenz Julienne <[email-masked]>
> ---
>
> Changes since RFC:
>   - Alphabetically ordered relevant stuff
>   - Updated Kconfig to select firmware interface
>   - Correctly unref clk_dev after use
>   - Remove all opps on failure
>   - Remove use of dev_pm_opp_set_sharing_cpus()
>
>  drivers/cpufreq/Kconfig.arm           |  8 +++
>  drivers/cpufreq/Makefile              |  1 +
>  drivers/cpufreq/raspberrypi-cpufreq.c | 84 +++++++++++++++++++++++++++
>  3 files changed, 93 insertions(+)
>  create mode 100644 drivers/cpufreq/raspberrypi-cpufreq.c
>
> diff --git a/drivers/cpufreq/Kconfig.arm b/drivers/cpufreq/Kconfig.arm
> index f8129edc145e..556d432cc826 100644
> --- a/drivers/cpufreq/Kconfig.arm
> +++ b/drivers/cpufreq/Kconfig.arm
> @@ -133,6 +133,14 @@ config ARM_QCOM_CPUFREQ_HW
>  	  The driver implements the cpufreq interface for this HW engine.
>  	  Say Y if you want to support CPUFreq HW.
>  
> +config ARM_RASPBERRYPI_CPUFREQ
> +	tristate "Raspberry Pi cpufreq support"
> +	select RASPBERRYPI_FIRMWARE
> +	help
> +	  This adds the CPUFreq driver for Raspberry Pi
> +
> +	  If in doubt, say N.
> +
>  config ARM_S3C_CPUFREQ
>  	bool
>  	help
> diff --git a/drivers/cpufreq/Makefile b/drivers/cpufreq/Makefile
> index 689b26c6f949..121c1acb66c0 100644
> --- a/drivers/cpufreq/Makefile
> +++ b/drivers/cpufreq/Makefile
> @@ -64,6 +64,7 @@ obj-$(CONFIG_ARM_PXA2xx_CPUFREQ)	+= pxa2xx-cpufreq.o
>  obj-$(CONFIG_PXA3xx)			+= pxa3xx-cpufreq.o
>  obj-$(CONFIG_ARM_QCOM_CPUFREQ_HW)	+= qcom-cpufreq-hw.o
>  obj-$(CONFIG_ARM_QCOM_CPUFREQ_KRYO)	+= qcom-cpufreq-kryo.o
> +obj-$(CONFIG_ARM_RASPBERRYPI_CPUFREQ) 	+= raspberrypi-cpufreq.o
>  obj-$(CONFIG_ARM_S3C2410_CPUFREQ)	+= s3c2410-cpufreq.o
>  obj-$(CONFIG_ARM_S3C2412_CPUFREQ)	+= s3c2412-cpufreq.o
>  obj-$(CONFIG_ARM_S3C2416_CPUFREQ)	+= s3c2416-cpufreq.o
> diff --git a/drivers/cpufreq/raspberrypi-cpufreq.c b/drivers/cpufreq/raspberrypi-cpufreq.c
> new file mode 100644
> index 000000000000..2b3a195a9d37
> --- /dev/null
> +++ b/drivers/cpufreq/raspberrypi-cpufreq.c
> @@ -0,0 +1,84 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Raspberry Pi cpufreq driver
> + *
> + * Copyright (C) 2019, Nicolas Saenz Julienne <[email-masked]>
> + */
> +
> +#include <linux/clk.h>
> +#include <linux/cpu.h>
> +#include <linux/cpufreq.h>
> +#include <linux/module.h>
> +#include <linux/of.h>
> +#include <linux/platform_device.h>
> +#include <linux/pm_opp.h>
> +
> +static const struct of_device_id machines[] __initconst = {
> +	{ .compatible = "raspberrypi,3-model-b-plus" },
> +	{ .compatible = "raspberrypi,3-model-b" },
> +	{ .compatible = "raspberrypi,2-model-b" },
> +	{ /* sentinel */ }
> +};

I think I'd skip the compatible string check here.  The firmware's
clock-management should be well-tested by folks playing with clocking in
the downstream tree.  There aren't any firmware differences in the
processing of these clock management packets, to my recollection.

Other than that, I'm happy with the series and would give it my
acked-by.
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