Re: [PATCH 2/4] clk: bcm283x: add driver interfacing with Raspberry Pi's firmware

[Nicolas Saenz Julienne]

Hi Stefan,
thanks for your review.

On Wed, 2019-06-05 at 12:44 +0200, Stefan Wahren wrote:
> Hi Nicolas,
> 
> Am 04.06.19 um 19:32 schrieb Nicolas Saenz Julienne:
> > Raspberry Pi's firmware offers and interface though which update it's
> > clock's frequencies. This is specially useful in order to change the CPU
> > clock (pllb_arm) which is 'owned' by the firmware and we're unable to
> > scale using the register interface.
> > 
> > Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@xxxxxxx>
> > ---
> > 
> > Changes since RFC:
> >   - Moved firmware interface into own driver
> >   - Use of_find_compatible_node()
> >   - Remove error message on rpi_firmware_get() failure
> >   - Ratelimit messages on set_rate() failure
> >   - Use __le32 on firmware interface definition
> > 
> >  drivers/clk/bcm/Makefile          |   1 +
> >  drivers/clk/bcm/clk-raspberrypi.c | 316 ++++++++++++++++++++++++++++++
> >  2 files changed, 317 insertions(+)
> >  create mode 100644 drivers/clk/bcm/clk-raspberrypi.c
> > 
> > diff --git a/drivers/clk/bcm/Makefile b/drivers/clk/bcm/Makefile
> > index 002661d39128..07abe92df9d1 100644
> > --- a/drivers/clk/bcm/Makefile
> > +++ b/drivers/clk/bcm/Makefile
> > @@ -7,6 +7,7 @@ obj-$(CONFIG_CLK_BCM_KONA)	+= clk-bcm21664.o
> >  obj-$(CONFIG_COMMON_CLK_IPROC)	+= clk-iproc-armpll.o clk-iproc-pll.o
> > clk-iproc-asiu.o
> >  obj-$(CONFIG_ARCH_BCM2835)	+= clk-bcm2835.o
> >  obj-$(CONFIG_ARCH_BCM2835)	+= clk-bcm2835-aux.o
> > +obj-$(CONFIG_ARCH_BCM2835)	+= clk-raspberrypi.o
> Hm, on the one side it would be nice to avoid building this driver in
> case the firmware driver is disabled on the other side it would be good
> to keep compile test.
> >  obj-$(CONFIG_ARCH_BCM_53573)	+= clk-bcm53573-ilp.o
> >  obj-$(CONFIG_CLK_BCM_CYGNUS)	+= clk-cygnus.o
> >  obj-$(CONFIG_CLK_BCM_HR2)	+= clk-hr2.o
> > diff --git a/drivers/clk/bcm/clk-raspberrypi.c b/drivers/clk/bcm/clk-
> > raspberrypi.c
> > new file mode 100644
> > index 000000000000..485c00288414
> > --- /dev/null
> > +++ b/drivers/clk/bcm/clk-raspberrypi.c
> > @@ -0,0 +1,316 @@
> > +// SPDX-License-Identifier: GPL-2.0+
> > +/*
> > + * Copyright (C) 2019 Nicolas Saenz Julienne
> > + */
> > +
> > +#include <linux/clkdev.h>
> > +#include <linux/clk-provider.h>
> > +#include <linux/io.h>
> > +#include <linux/module.h>
> > +#include <linux/platform_device.h>
> > +
> > +#include <soc/bcm2835/raspberrypi-firmware.h>
> > +
> > +#define RPI_FIRMWARE_ARM_CLK_ID		0x000000003
> > +
> > +#define RPI_FIRMWARE_STATE_ENABLE_BIT	0x1
> > +#define RPI_FIRMWARE_STATE_WAIT_BIT	0x2
> how about using the BIT() macro?
> > +
> > +/*
> > + * Even though the firmware interface alters 'pllb' the frequencies are
> > + * provided as per 'pllb_arm'. We need to scale before passing them trough.
> > + */
> > +#define RPI_FIRMWARE_PLLB_ARM_DIV_RATE	2
> > +
> > +#define A2W_PLL_FRAC_BITS		20
> > +
> > +struct raspberrypi_clk {
> > +	struct device *dev;
> > +	struct rpi_firmware *firmware;
> > +
> > +	unsigned long min_rate;
> > +	unsigned long max_rate;
> > +
> > +	struct clk_hw pllb;
> > +	struct clk_hw *pllb_arm;
> > +	struct clk_lookup *pllb_arm_lookup;
> > +};
> > +
> > +/*
> > + * Structure of the message passed to Raspberry Pi's firmware in order to
> > + * change clock rates. The 'disable_turbo' option is only available to the
> > ARM
> > + * clock (pllb) which we enable by default as turbo mode will alter
> > multiple
> > + * clocks at once.
> > + *
> > + * Even though we're able to access the clock registers directly we're
> > bound to
> > + * use the firmware interface as the firmware ultimately takes care of
> > + * mitigating overheating/undervoltage situations and we would be changing
> > + * frequencies behind his back.
> > + *
> > + * For more information on the firmware interface check:
> > + * https://github.com/raspberrypi/firmware/wiki/Mailbox-property-interface
> > + */
> > +struct raspberrypi_firmware_prop {
> > +	__le32 id;
> > +	__le32 val;
> > +	__le32 disable_turbo;
> > +} __packed;
> > +
> > +static int raspberrypi_clock_property(struct rpi_firmware *firmware, u32
> > tag,
> > +				      u32 clk, u32 *val)
> > +{
> > +	struct raspberrypi_firmware_prop msg = {
> > +		.id = clk,
> > +		.val = *val,
> > +		.disable_turbo = 1,
> > +	};
> > +	int ret;
> > +
> > +	ret = rpi_firmware_property(firmware, tag, &msg, sizeof(msg));
> > +	if (ret)
> > +		return ret;
> > +
> > +	*val = msg.val;
> > +
> > +	return 0;
> > +}
> > +
> > +static int raspberrypi_fw_pll_is_on(struct clk_hw *hw)
> > +{
> > +	struct raspberrypi_clk *rpi = container_of(hw, struct raspberrypi_clk,
> > +						   pllb);
> > +	u32 val = 0;
> > +	int ret;
> > +
> > +	ret = raspberrypi_clock_property(rpi->firmware,
> > +					 RPI_FIRMWARE_GET_CLOCK_STATE,
> > +					 RPI_FIRMWARE_ARM_CLK_ID, &val);
> > +	if (ret)
> > +		return 0;
> > +
> > +	return !!(val & RPI_FIRMWARE_STATE_ENABLE_BIT);
> > +}
> > +
> > +
> > +static unsigned long raspberrypi_fw_pll_get_rate(struct clk_hw *hw,
> > +						 unsigned long parent_rate)
> > +{
> > +	struct raspberrypi_clk *rpi = container_of(hw, struct raspberrypi_clk,
> > +						   pllb);
> > +	u32 val = 0;
> > +	int ret;
> > +
> > +	ret = raspberrypi_clock_property(rpi->firmware,
> > +					 RPI_FIRMWARE_GET_CLOCK_RATE,
> > +					 RPI_FIRMWARE_ARM_CLK_ID,
> > +					 &val);
> > +	if (ret)
> > +		return ret;
> > +
> > +	return val * RPI_FIRMWARE_PLLB_ARM_DIV_RATE;
> > +}
> > +
> > +static int raspberrypi_fw_pll_on(struct clk_hw *hw)
> > +{
> > +	struct raspberrypi_clk *rpi = container_of(hw, struct raspberrypi_clk,
> > +						   pllb);
> > +	u32 val;
> > +	int ret;
> > +
> > +	val = RPI_FIRMWARE_STATE_ENABLE_BIT | RPI_FIRMWARE_STATE_WAIT_BIT;
> > +
> > +	ret = raspberrypi_clock_property(rpi->firmware,
> > +					 RPI_FIRMWARE_SET_CLOCK_STATE,
> > +					 RPI_FIRMWARE_ARM_CLK_ID, &val);
> > +	if (ret)
> > +		return ret;
> > +
> > +	return 0;
> return ret;
> > +}
> > +
> > +static int raspberrypi_fw_pll_set_rate(struct clk_hw *hw, unsigned long
> > rate,
> > +				       unsigned long parent_rate)
> > +{
> > +	struct raspberrypi_clk *rpi = container_of(hw, struct raspberrypi_clk,
> > +						   pllb);
> > +	u32 new_rate = rate / RPI_FIRMWARE_PLLB_ARM_DIV_RATE;
> > +	int ret;
> > +
> > +	ret = raspberrypi_clock_property(rpi->firmware,
> > +					 RPI_FIRMWARE_SET_CLOCK_RATE,
> > +					 RPI_FIRMWARE_ARM_CLK_ID,
> > +					 &new_rate);
> > +	if (ret)
> > +		dev_err_ratelimited(rpi->dev, "Failed to change %s frequency:
> > %d",
> > +				    clk_hw_get_name(hw), ret);
> > +
> > +	return ret;
> > +}
> > +
> > +/*
> > + * Sadly there is no firmware rate rounding interface. We borred it from
> borrowed?

Yes

> > + * clk-bcm2835.
> > + */
> > +static long raspberrypi_pll_round_rate(struct clk_hw *hw, unsigned long
> > rate,
> > +				       unsigned long *parent_rate)
> > +{
> > +	struct raspberrypi_clk *rpi = container_of(hw, struct raspberrypi_clk,
> > +						   pllb);
> > +	u64 div, final_rate;
> > +	u32 ndiv, fdiv;
> > +
> > +	rate = clamp(rate, rpi->min_rate, rpi->max_rate);
> > +
> > +	div = (u64)rate << A2W_PLL_FRAC_BITS;
> > +	do_div(div, *parent_rate);
> > +
> > +	ndiv = div >> A2W_PLL_FRAC_BITS;
> > +	fdiv = div & ((1 << A2W_PLL_FRAC_BITS) - 1);
> > +
> > +	/* We can't use rate directly as it would overflow */
> > +	final_rate = ((u64)*parent_rate * ((ndiv << A2W_PLL_FRAC_BITS) + fdiv));
> > +
> > +	return final_rate >> A2W_PLL_FRAC_BITS;
> > +}
> > +
> > +static void raspberrypi_fw_pll_off(struct clk_hw *hw)
> > +{
> > +	struct raspberrypi_clk *rpi = container_of(hw, struct raspberrypi_clk,
> > +						   pllb);
> > +	u32 val = RPI_FIRMWARE_STATE_WAIT_BIT;
> > +
> > +	raspberrypi_clock_property(rpi->firmware,
> > +				   RPI_FIRMWARE_SET_CLOCK_STATE,
> > +				   RPI_FIRMWARE_ARM_CLK_ID, &val);
> > +}
> I'm not sure. Does this operation really make sense?

You're right, I implemented it mindlessly as I saw the API available in the
firmware interface. I'll remove both prepare and unprepare as one is redundant
and the other harmful (though I wonder what whould happen if called).

Regards,
Nicolas

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