Date:   Sun, 17 Oct 2021 13:27:59 +0200
From:   "Sven Peter" <sven@...npeter.dev>
To:     "Mark Kettenis" <mark.kettenis@...all.nl>
Cc:     "Jassi Brar" <jassisinghbrar@...il.com>,
        "Rob Herring" <robh+dt@...nel.org>,
        "Hector Martin" <marcan@...can.st>,
        "Alyssa Rosenzweig" <alyssa@...enzweig.io>,
        mohamed.mediouni@...amail.com,
        "Stan Skowronek" <stan@...ellium.com>, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] mailbox: apple: Add driver for Apple mailboxes


Hi Mark,

On Sun, Oct 17, 2021, at 13:25, Mark Kettenis wrote:
>> From: Sven Peter <sven@...npeter.dev>
>> Date: Thu, 16 Sep 2021 17:49:11 +0200
>
> Hi Sven,
>
>> Apple SoCs such as the M1 come with various co-processors. Mailboxes
>> are used to communicate with those. This driver adds support for
>> two variants of those mailboxes.
>> 
>> Signed-off-by: Sven Peter <sven@...npeter.dev>
>> ---
>>  MAINTAINERS                     |   2 +
>>  drivers/mailbox/Kconfig         |  12 +
>>  drivers/mailbox/Makefile        |   2 +
>>  drivers/mailbox/apple-mailbox.c | 431 ++++++++++++++++++++++++++++++++
>>  include/linux/apple-mailbox.h   |  18 ++
>>  5 files changed, 465 insertions(+)
>>  create mode 100644 drivers/mailbox/apple-mailbox.c
>>  create mode 100644 include/linux/apple-mailbox.h
>> 
>> diff --git a/MAINTAINERS b/MAINTAINERS
>> index 47de27282c98..cf0500bbea5b 100644
>> --- a/MAINTAINERS
>> +++ b/MAINTAINERS
>> @@ -1724,8 +1724,10 @@ F:	Documentation/devicetree/bindings/mailbox/apple,mailbox.yaml
>>  F:	Documentation/devicetree/bindings/pinctrl/apple,pinctrl.yaml
>>  F:	arch/arm64/boot/dts/apple/
>>  F:	drivers/irqchip/irq-apple-aic.c
>> +F:	drivers/mailbox/apple-mailbox.c
>>  F:	include/dt-bindings/interrupt-controller/apple-aic.h
>>  F:	include/dt-bindings/pinctrl/apple.h
>> +F:	include/linux/apple-mailbox.h
>>  
>>  ARM/ARTPEC MACHINE SUPPORT
>>  M:	Jesper Nilsson <jesper.nilsson@...s.com>
>> diff --git a/drivers/mailbox/Kconfig b/drivers/mailbox/Kconfig
>> index c9fc06c7e685..d9cd3606040e 100644
>> --- a/drivers/mailbox/Kconfig
>> +++ b/drivers/mailbox/Kconfig
>> @@ -8,6 +8,18 @@ menuconfig MAILBOX
>>  
>>  if MAILBOX
>>  
>> +config APPLE_MAILBOX
>> +	tristate "Apple Mailbox driver"
>> +	depends on ARCH_APPLE || (ARM64 && COMPILE_TEST)
>> +	default ARCH_APPLE
>> +	help
>> +	  Apple SoCs have various co-processors required for certain
>> +	  peripherals to work (NVMe, display controller, etc.). This
>> +	  driver adds support for the mailbox controller used to
>> +	  communicate with those.
>> +
>> +	  Say Y here if you have a Apple SoC.
>> +
>>  config ARM_MHU
>>  	tristate "ARM MHU Mailbox"
>>  	depends on ARM_AMBA
>> diff --git a/drivers/mailbox/Makefile b/drivers/mailbox/Makefile
>> index c2089f04887e..338cc05e5431 100644
>> --- a/drivers/mailbox/Makefile
>> +++ b/drivers/mailbox/Makefile
>> @@ -58,3 +58,5 @@ obj-$(CONFIG_SUN6I_MSGBOX)	+= sun6i-msgbox.o
>>  obj-$(CONFIG_SPRD_MBOX)		+= sprd-mailbox.o
>>  
>>  obj-$(CONFIG_QCOM_IPCC)		+= qcom-ipcc.o
>> +
>> +obj-$(CONFIG_APPLE_MAILBOX)	+= apple-mailbox.o
>> diff --git a/drivers/mailbox/apple-mailbox.c b/drivers/mailbox/apple-mailbox.c
>> new file mode 100644
>> index 000000000000..2622a6369075
>> --- /dev/null
>> +++ b/drivers/mailbox/apple-mailbox.c
>> @@ -0,0 +1,431 @@
>> +// SPDX-License-Identifier: GPL-2.0-only OR MIT
>> +/*
>> + * Apple mailbox driver
>> + *
>> + * Copyright (C) 2021 The Asahi Linux Contributors
>> + *
>> + * This driver adds support for two mailbox variants (called ASC and M3 by
>> + * Apple) found in Apple SoCs such as the M1. It consists of two FIFOs used to
>> + * exchange 64+32 bit messages between the main CPU and a co-processor.
>> + * Various coprocessors implement different IPC protocols based on these simple
>> + * messages and shared memory buffers.
>> + *
>> + * Both the main CPU and the co-processor see the same set of registers but
>> + * the first FIFO (A2I) is always used to transfer messages from the application
>> + * processor (us) to the I/O processor and the second one (I2A) for the
>> + * other direction.
>> + */
>> +
>> +#include <linux/apple-mailbox.h>
>> +#include <linux/clk.h>
>> +#include <linux/device.h>
>> +#include <linux/gfp.h>
>> +#include <linux/interrupt.h>
>> +#include <linux/io.h>
>> +#include <linux/mailbox_controller.h>
>> +#include <linux/module.h>
>> +#include <linux/of.h>
>> +#include <linux/platform_device.h>
>> +#include <linux/types.h>
>> +
>> +#define APPLE_ASC_MBOX_CONTROL_FULL  BIT(16)
>> +#define APPLE_ASC_MBOX_CONTROL_EMPTY BIT(17)
>> +
>> +#define APPLE_ASC_MBOX_A2I_CONTROL 0x110
>> +#define APPLE_ASC_MBOX_A2I_SEND0   0x800
>> +#define APPLE_ASC_MBOX_A2I_SEND1   0x808
>> +#define APPLE_ASC_MBOX_A2I_RECV0   0x810
>> +#define APPLE_ASC_MBOX_A2I_RECV1   0x818
>> +
>> +#define APPLE_ASC_MBOX_I2A_CONTROL 0x114
>> +#define APPLE_ASC_MBOX_I2A_SEND0   0x820
>> +#define APPLE_ASC_MBOX_I2A_SEND1   0x828
>> +#define APPLE_ASC_MBOX_I2A_RECV0   0x830
>> +#define APPLE_ASC_MBOX_I2A_RECV1   0x838
>> +
>> +#define APPLE_M3_MBOX_CONTROL_FULL  BIT(16)
>> +#define APPLE_M3_MBOX_CONTROL_EMPTY BIT(17)
>> +
>> +#define APPLE_M3_MBOX_A2I_CONTROL 0x50
>> +#define APPLE_M3_MBOX_A2I_SEND0	  0x60
>> +#define APPLE_M3_MBOX_A2I_SEND1	  0x68
>> +#define APPLE_M3_MBOX_A2I_RECV0	  0x70
>> +#define APPLE_M3_MBOX_A2I_RECV1	  0x78
>> +
>> +#define APPLE_M3_MBOX_I2A_CONTROL 0x80
>> +#define APPLE_M3_MBOX_I2A_SEND0	  0x90
>> +#define APPLE_M3_MBOX_I2A_SEND1	  0x98
>> +#define APPLE_M3_MBOX_I2A_RECV0	  0xa0
>> +#define APPLE_M3_MBOX_I2A_RECV1	  0xa8
>> +
>> +#define APPLE_M3_MBOX_IRQ_ENABLE	0x48
>> +#define APPLE_M3_MBOX_IRQ_ACK		0x4c
>> +#define APPLE_M3_MBOX_IRQ_A2I_EMPTY	BIT(0)
>> +#define APPLE_M3_MBOX_IRQ_A2I_NOT_EMPTY BIT(1)
>> +#define APPLE_M3_MBOX_IRQ_I2A_EMPTY	BIT(2)
>> +#define APPLE_M3_MBOX_IRQ_I2A_NOT_EMPTY BIT(3)
>> +
>> +#define APPLE_MBOX_MSG1_OUTCNT GENMASK(56, 52)
>> +#define APPLE_MBOX_MSG1_INCNT  GENMASK(51, 48)
>> +#define APPLE_MBOX_MSG1_OUTPTR GENMASK(47, 44)
>> +#define APPLE_MBOX_MSG1_INPTR  GENMASK(43, 40)
>> +#define APPLE_MBOX_MSG1_MSG    GENMASK(31, 0)
>> +
>> +struct apple_mbox_hw {
>> +	unsigned int control_full;
>> +	unsigned int control_empty;
>> +
>> +	unsigned int a2i_control;
>> +	unsigned int a2i_send0;
>> +	unsigned int a2i_send1;
>> +
>> +	unsigned int i2a_control;
>> +	unsigned int i2a_recv0;
>> +	unsigned int i2a_recv1;
>> +
>> +	bool has_irq_controls;
>> +	unsigned int irq_enable;
>> +	unsigned int irq_ack;
>> +	unsigned int irq_bit_recv_not_empty;
>> +	unsigned int irq_bit_send_empty;
>> +};
>> +
>> +static const struct apple_mbox_hw apple_mbox_asc_hw = {
>> +	.control_full = APPLE_ASC_MBOX_CONTROL_FULL,
>> +	.control_empty = APPLE_ASC_MBOX_CONTROL_EMPTY,
>> +
>> +	.a2i_control = APPLE_ASC_MBOX_A2I_CONTROL,
>> +	.a2i_send0 = APPLE_ASC_MBOX_A2I_SEND0,
>> +	.a2i_send1 = APPLE_ASC_MBOX_A2I_SEND1,
>> +
>> +	.i2a_control = APPLE_ASC_MBOX_I2A_CONTROL,
>> +	.i2a_recv0 = APPLE_ASC_MBOX_I2A_RECV0,
>> +	.i2a_recv1 = APPLE_ASC_MBOX_I2A_RECV1,
>> +
>> +	.has_irq_controls = false,
>> +};
>> +
>> +static const struct apple_mbox_hw apple_mbox_m3_hw = {
>> +	.control_full = APPLE_M3_MBOX_CONTROL_FULL,
>> +	.control_empty = APPLE_M3_MBOX_CONTROL_EMPTY,
>> +
>> +	.a2i_control = APPLE_M3_MBOX_A2I_CONTROL,
>> +	.a2i_send0 = APPLE_M3_MBOX_A2I_SEND0,
>> +	.a2i_send1 = APPLE_M3_MBOX_A2I_SEND1,
>> +
>> +	.i2a_control = APPLE_M3_MBOX_I2A_CONTROL,
>> +	.i2a_recv0 = APPLE_M3_MBOX_I2A_RECV0,
>> +	.i2a_recv1 = APPLE_M3_MBOX_I2A_RECV1,
>> +
>> +	.has_irq_controls = true,
>> +	.irq_enable = APPLE_M3_MBOX_IRQ_ENABLE,
>> +	.irq_ack = APPLE_M3_MBOX_IRQ_ACK,
>> +	.irq_bit_recv_not_empty = APPLE_M3_MBOX_IRQ_I2A_NOT_EMPTY,
>> +	.irq_bit_send_empty = APPLE_M3_MBOX_IRQ_A2I_EMPTY,
>> +};
>> +
>> +static const struct of_device_id apple_mbox_of_match[] = {
>> +	{ .compatible = "apple,t8103-asc-mailbox", .data = &apple_mbox_asc_hw },
>> +	{ .compatible = "apple,t8103-m3-mailbox", .data = &apple_mbox_m3_hw },
>> +	{}
>> +};
>> +MODULE_DEVICE_TABLE(of, apple_mbox_of_match);
>> +
>> +struct apple_mbox {
>> +	void __iomem *regs;
>> +	const struct apple_mbox_hw *hw;
>> +
>> +	int irq_recv_not_empty;
>> +	int irq_send_empty;
>> +
>> +	struct clk_bulk_data *clks;
>> +	int num_clks;
>> +
>> +	struct mbox_chan chan;
>> +
>> +	struct device *dev;
>> +	struct mbox_controller controller;
>> +};
>> +
>> +static bool apple_mbox_hw_can_send(struct apple_mbox *apple_mbox)
>> +{
>> +	u32 mbox_ctrl =
>> +		readl_relaxed(apple_mbox->regs + apple_mbox->hw->a2i_control);
>> +
>> +	return !(mbox_ctrl & apple_mbox->hw->control_full);
>> +}
>> +
>> +static int apple_mbox_hw_send(struct apple_mbox *apple_mbox,
>> +			      struct apple_mbox_msg *msg)
>> +{
>> +	if (!apple_mbox_hw_can_send(apple_mbox))
>> +		return -EBUSY;
>> +
>> +	dev_dbg(apple_mbox->dev, "> TX %016llx %08x\n", msg->msg0, msg->msg1);
>> +
>> +	/*
>> +	 * This message may be related to a shared memory buffer and we must
>> +	 * ensure all previous writes to normal memory are visible before
>> +	 * submitting it.
>> +	 */
>> +	dma_wmb();
>> +
>> +	writeq_relaxed(msg->msg0, apple_mbox->regs + apple_mbox->hw->a2i_send0);
>> +	writeq_relaxed(FIELD_PREP(APPLE_MBOX_MSG1_MSG, msg->msg1),
>> +		       apple_mbox->regs + apple_mbox->hw->a2i_send1);
>> +
>> +	return 0;
>> +}
>> +
>> +static bool apple_mbox_hw_can_recv(struct apple_mbox *apple_mbox)
>> +{
>> +	u32 mbox_ctrl =
>> +		readl_relaxed(apple_mbox->regs + apple_mbox->hw->i2a_control);
>> +
>> +	return !(mbox_ctrl & apple_mbox->hw->control_empty);
>> +}
>> +
>> +static int apple_mbox_hw_recv(struct apple_mbox *apple_mbox,
>> +			      struct apple_mbox_msg *msg)
>> +{
>> +	if (!apple_mbox_hw_can_recv(apple_mbox))
>> +		return -ENOMSG;
>> +
>> +	msg->msg0 = readq_relaxed(apple_mbox->regs + apple_mbox->hw->i2a_recv0);
>> +	msg->msg1 = FIELD_GET(
>> +		APPLE_MBOX_MSG1_MSG,
>> +		readq_relaxed(apple_mbox->regs + apple_mbox->hw->i2a_recv1));
>> +
>> +	dev_dbg(apple_mbox->dev, "< RX %016llx %08x\n", msg->msg0, msg->msg1);
>> +
>> +	/*
>> +	 * This message may be related to a shared memory buffer and we must
>> +	 * ensure any following reads from normal memory only happen after
>> +	 * having read this message.
>> +	 */
>> +	dma_rmb();
>> +
>> +	return 0;
>> +}
>> +
>> +static int apple_mbox_chan_send_data(struct mbox_chan *chan, void *data)
>> +{
>> +	struct apple_mbox *apple_mbox = chan->con_priv;
>> +	struct apple_mbox_msg *msg = data;
>> +	int ret;
>> +
>> +	ret = apple_mbox_hw_send(apple_mbox, msg);
>> +	if (ret)
>> +		return ret;
>> +
>> +	/*
>> +	 * The interrupt is level triggered and will keep firing as long as the
>> +	 * FIFO is empty. It will also keep firing if the FIFO was empty
>> +	 * at any point in the past until it has been acknowledged at the
>> +	 * mailbox level. By acknowledging it here we can ensure that we will
>> +	 * only get the interrupt once the FIFO has been cleared again.
>> +	 * If the FIFO is already empty before the ack it will fire again
>> +	 * immediately after the ack.
>> +	 */
>> +	if (apple_mbox->hw->has_irq_controls) {
>> +		writel_relaxed(apple_mbox->hw->irq_bit_send_empty,
>> +			       apple_mbox->regs + apple_mbox->hw->irq_ack);
>> +	}
>> +	enable_irq(apple_mbox->irq_send_empty);
>> +
>> +	return 0;
>> +}
>> +
>> +static irqreturn_t apple_mbox_send_empty_irq(int irq, void *data)
>> +{
>> +	struct apple_mbox *apple_mbox = data;
>> +
>> +	/*
>> +	 * We don't need to acknowledge the interrupt at the mailbox level
>> +	 * here even if supported by the hardware. It will keep firing but that
>> +	 * doesn't matter since it's disabled at the main interrupt controller.
>> +	 * apple_mbox_chan_send_data will acknowledge it before enabling
>> +	 * it at the main controller again.
>> +	 */
>> +	disable_irq_nosync(apple_mbox->irq_send_empty);
>> +	mbox_chan_txdone(&apple_mbox->chan, 0);
>> +	return IRQ_HANDLED;
>> +}
>> +
>> +static irqreturn_t apple_mbox_recv_irq(int irq, void *data)
>> +{
>> +	struct apple_mbox *apple_mbox = data;
>> +	struct apple_mbox_msg msg;
>> +
>> +	while (apple_mbox_hw_recv(apple_mbox, &msg) == 0)
>> +		mbox_chan_received_data(&apple_mbox->chan, (void *)&msg);
>> +
>> +	/*
>> +	 * The interrupt will keep firing even if there are no more messages
>> +	 * unless we also acknowledge it at the mailbox level here.
>> +	 * There's no race if a message comes in between the check in the while
>> +	 * loop above and the ack below: If a new messages arrives inbetween
>> +	 * those two the interrupt will just fire again immediately after the
>> +	 * ack since it's level triggered.
>> +	 */
>> +	if (apple_mbox->hw->has_irq_controls) {
>> +		writel_relaxed(apple_mbox->hw->irq_bit_recv_not_empty,
>> +			       apple_mbox->regs + apple_mbox->hw->irq_ack);
>> +	}
>> +
>> +	return IRQ_HANDLED;
>> +}
>> +
>> +static struct mbox_chan *apple_mbox_of_xlate(struct mbox_controller *mbox,
>> +					     const struct of_phandle_args *spec)
>> +{
>> +	struct apple_mbox *apple_mbox = dev_get_drvdata(mbox->dev);
>> +
>> +	if (spec->args_count != 0)
>> +		return ERR_PTR(-EINVAL);
>> +	if (apple_mbox->chan.con_priv)
>> +		return ERR_PTR(-EBUSY);
>> +
>> +	apple_mbox->chan.con_priv = apple_mbox;
>> +	return &apple_mbox->chan;
>> +}
>> +
>> +static int apple_mbox_chan_startup(struct mbox_chan *chan)
>> +{
>> +	struct apple_mbox *apple_mbox = chan->con_priv;
>> +
>> +	/*
>> +	 * Only some variants of this mailbox HW provide interrupt control
>> +	 * at the mailbox level. We therefore need to handle enabling/disabling
>> +	 * interrupts at the main interrupt controller anyway for hardware that
>> +	 * doesn't. Just always keep the interrupts we care about enabled at
>> +	 * the mailbox level so that both hardware revisions behave almost
>> +	 * the same.
>> +	 */
>> +	if (apple_mbox->hw->has_irq_controls) {
>> +		writel_relaxed(apple_mbox->hw->irq_bit_recv_not_empty |
>> +				       apple_mbox->hw->irq_bit_send_empty,
>> +			       apple_mbox->regs + apple_mbox->hw->irq_enable);
>> +	}
>> +
>> +	enable_irq(apple_mbox->irq_recv_not_empty);
>> +	return 0;
>> +}
>> +
>> +static void apple_mbox_chan_shutdown(struct mbox_chan *chan)
>> +{
>> +	struct apple_mbox *apple_mbox = chan->con_priv;
>> +
>> +	disable_irq(apple_mbox->irq_recv_not_empty);
>> +}
>> +
>> +static const struct mbox_chan_ops apple_mbox_ops = {
>> +	.send_data = apple_mbox_chan_send_data,
>> +	.startup = apple_mbox_chan_startup,
>> +	.shutdown = apple_mbox_chan_shutdown,
>> +};
>> +
>> +static int apple_mbox_probe(struct platform_device *pdev)
>> +{
>> +	int ret;
>> +	const struct of_device_id *match;
>> +	char *irqname;
>> +	struct apple_mbox *mbox;
>> +	struct device *dev = &pdev->dev;
>> +
>> +	match = of_match_node(apple_mbox_of_match, pdev->dev.of_node);
>> +	if (!match)
>> +		return -EINVAL;
>> +	if (!match->data)
>> +		return -EINVAL;
>> +
>> +	mbox = devm_kzalloc(dev, sizeof(*mbox), GFP_KERNEL);
>> +	if (!mbox)
>> +		return -ENOMEM;
>> +	platform_set_drvdata(pdev, mbox);
>> +
>> +	mbox->dev = dev;
>> +	mbox->regs = devm_platform_ioremap_resource(pdev, 0);
>> +	if (IS_ERR(mbox->regs))
>> +		return PTR_ERR(mbox->regs);
>> +
>> +	mbox->hw = match->data;
>> +	mbox->irq_recv_not_empty =
>> +		platform_get_irq_byname(pdev, "recv-not-empty");
>> +	if (mbox->irq_recv_not_empty < 0)
>> +		return -ENODEV;
>> +
>> +	mbox->irq_send_empty = platform_get_irq_byname(pdev, "send-empty");
>> +	if (mbox->irq_send_empty < 0)
>> +		return -ENODEV;
>> +
>> +	ret = devm_clk_bulk_get_all(dev, &mbox->clks);
>> +	if (ret < 0)
>> +		return ret;
>> +	mbox->num_clks = ret;
>> +
>> +	ret = clk_bulk_prepare_enable(mbox->num_clks, mbox->clks);
>> +	if (ret)
>> +		return ret;
>
> Given that we now realized that the clocks are really power domains,
> the clock code should probably be dropped.  Makes the driver smaller
> since power domains are handle automatically by the core device code.
>

Yup, thanks for pointing that out! I'll drop it from the code
and the binding for v3.



Sven

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