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Date:   Tue, 20 Aug 2019 15:34:41 +0200
From:   =?utf-8?Q?Ond=C5=99ej?= Jirman <megous@megous.com>
To:     Samuel Holland <samuel@sholland.org>
Cc:     Maxime Ripard <maxime.ripard@bootlin.com>,
        Chen-Yu Tsai <wens@csie.org>,
        Jassi Brar <jassisinghbrar@gmail.com>,
        Michael Turquette <mturquette@baylibre.com>,
        Stephen Boyd <sboyd@kernel.org>,
        Rob Herring <robh+dt@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Corentin Labbe <clabbe.montjoie@gmail.com>,
        Vasily Khoruzhick <anarsoul@gmail.com>,
        devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-sunxi@googlegroups.com, linux-clk@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v4 04/10] mailbox: sunxi-msgbox: Add a new mailbox driver
Message-ID: <20190820133441.g56apl2oclioi4ts@core.my.home>
Mail-Followup-To: Samuel Holland <samuel@sholland.org>,
        Maxime Ripard <maxime.ripard@bootlin.com>,
        Chen-Yu Tsai <wens@csie.org>, Jassi Brar <jassisinghbrar@gmail.com>,
        Michael Turquette <mturquette@baylibre.com>,
        Stephen Boyd <sboyd@kernel.org>, Rob Herring <robh+dt@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Corentin Labbe <clabbe.montjoie@gmail.com>,
        Vasily Khoruzhick <anarsoul@gmail.com>, devicetree@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-sunxi@googlegroups.com,
        linux-clk@vger.kernel.org, linux-arm-kernel@lists.infradead.org
References: <20190820032311.6506-1-samuel@sholland.org>
 <20190820032311.6506-5-samuel@sholland.org>
 <20190820111825.2w55fleehrnon27u@core.my.home>
 <bc09e14c-1cf5-8124-fc34-c651b78577ce@sholland.org>
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Hi,

On Tue, Aug 20, 2019 at 08:07:53AM -0500, Samuel Holland wrote:
> On 8/20/19 6:18 AM, Ondřej Jirman wrote:
> > Hi Samuel,
> > 
> > On Mon, Aug 19, 2019 at 10:23:05PM -0500, Samuel Holland wrote:
> >> Allwinner sun8i, sun9i, and sun50i SoCs contain a hardware message box
> >> used for communication between the ARM CPUs and the ARISC management
> >> coprocessor. The hardware contains 8 unidirectional 4-message FIFOs.
> >>
> >> Add a driver for it, so it can be used for SCPI or other communication
> >> protocols.
> >>
> >> Signed-off-by: Samuel Holland <samuel@sholland.org>
> >> ---
> >>  drivers/mailbox/Kconfig        |  10 +
> >>  drivers/mailbox/Makefile       |   2 +
> >>  drivers/mailbox/sunxi-msgbox.c | 323 +++++++++++++++++++++++++++++++++
> >>  3 files changed, 335 insertions(+)
> >>  create mode 100644 drivers/mailbox/sunxi-msgbox.c
> >>
> >> diff --git a/drivers/mailbox/Kconfig b/drivers/mailbox/Kconfig
> >> index ab4eb750bbdd..57d12936175e 100644
> >> --- a/drivers/mailbox/Kconfig
> >> +++ b/drivers/mailbox/Kconfig
> >> @@ -227,4 +227,14 @@ config ZYNQMP_IPI_MBOX
> >>  	  message to the IPI buffer and will access the IPI control
> >>  	  registers to kick the other processor or enquire status.
> >>  
> >> +config SUNXI_MSGBOX
> >> +	tristate "Allwinner sunxi Message Box"
> >> +	depends on ARCH_SUNXI || COMPILE_TEST
> >> +	default ARCH_SUNXI
> >> +	help
> >> +	  Mailbox implementation for the hardware message box present in
> >> +	  Allwinner sun8i, sun9i, and sun50i SoCs. The hardware message box is
> >> +	  used for communication between the application CPUs and the power
> >> +	  management coprocessor.
> >> +
> >>  endif
> >> diff --git a/drivers/mailbox/Makefile b/drivers/mailbox/Makefile
> >> index c22fad6f696b..bec2d50b0976 100644
> >> --- a/drivers/mailbox/Makefile
> >> +++ b/drivers/mailbox/Makefile
> >> @@ -48,3 +48,5 @@ obj-$(CONFIG_STM32_IPCC) 	+= stm32-ipcc.o
> >>  obj-$(CONFIG_MTK_CMDQ_MBOX)	+= mtk-cmdq-mailbox.o
> >>  
> >>  obj-$(CONFIG_ZYNQMP_IPI_MBOX)	+= zynqmp-ipi-mailbox.o
> >> +
> >> +obj-$(CONFIG_SUNXI_MSGBOX)	+= sunxi-msgbox.o
> >> diff --git a/drivers/mailbox/sunxi-msgbox.c b/drivers/mailbox/sunxi-msgbox.c
> >> new file mode 100644
> >> index 000000000000..29a5101a5390
> >> --- /dev/null
> >> +++ b/drivers/mailbox/sunxi-msgbox.c
> >> @@ -0,0 +1,323 @@
> >> +// SPDX-License-Identifier: GPL-2.0
> >> +//
> >> +// Copyright (c) 2017-2019 Samuel Holland <samuel@sholland.org>
> >> +
> >> +#include <linux/bitops.h>
> >> +#include <linux/clk.h>
> >> +#include <linux/device.h>
> >> +#include <linux/err.h>
> >> +#include <linux/interrupt.h>
> >> +#include <linux/io.h>
> >> +#include <linux/kernel.h>
> >> +#include <linux/mailbox_controller.h>
> >> +#include <linux/module.h>
> >> +#include <linux/of.h>
> >> +#include <linux/of_irq.h>
> >> +#include <linux/platform_device.h>
> >> +#include <linux/reset.h>
> >> +#include <linux/spinlock.h>
> >> +
> >> +#define NUM_CHANS		8
> >> +
> >> +#define CTRL_REG(n)		(0x0000 + 0x4 * ((n) / 4))
> >> +#define CTRL_RX(n)		BIT(0 + 8 * ((n) % 4))
> >> +#define CTRL_TX(n)		BIT(4 + 8 * ((n) % 4))
> >> +
> >> +#define REMOTE_IRQ_EN_REG	0x0040
> >> +#define REMOTE_IRQ_STAT_REG	0x0050
> >> +#define LOCAL_IRQ_EN_REG	0x0060
> >> +#define LOCAL_IRQ_STAT_REG	0x0070
> >> +
> >> +#define RX_IRQ(n)		BIT(0 + 2 * (n))
> >> +#define RX_IRQ_MASK		0x5555
> >> +#define TX_IRQ(n)		BIT(1 + 2 * (n))
> >> +#define TX_IRQ_MASK		0xaaaa
> >> +
> >> +#define FIFO_STAT_REG(n)	(0x0100 + 0x4 * (n))
> >> +#define FIFO_STAT_MASK		GENMASK(0, 0)
> >> +
> >> +#define MSG_STAT_REG(n)		(0x0140 + 0x4 * (n))
> >> +#define MSG_STAT_MASK		GENMASK(2, 0)
> >> +
> >> +#define MSG_DATA_REG(n)		(0x0180 + 0x4 * (n))
> >> +
> >> +#define mbox_dbg(mbox, ...)	dev_dbg((mbox)->controller.dev, __VA_ARGS__)
> >> +
> >> +struct sunxi_msgbox {
> >> +	struct mbox_controller controller;
> >> +	struct clk *clk;
> >> +	spinlock_t lock;
> >> +	void __iomem *regs;
> >> +};
> >> +
> >> +static bool sunxi_msgbox_last_tx_done(struct mbox_chan *chan);
> >> +static bool sunxi_msgbox_peek_data(struct mbox_chan *chan);
> >> +
> >> +static inline int channel_number(struct mbox_chan *chan)
> >> +{
> >> +	return chan - chan->mbox->chans;
> >> +}
> >> +
> >> +static inline struct sunxi_msgbox *channel_to_msgbox(struct mbox_chan *chan)
> >> +{
> >> +	return chan->con_priv;
> >> +}
> >> +
> >> +static irqreturn_t sunxi_msgbox_irq(int irq, void *dev_id)
> >> +{
> >> +	struct sunxi_msgbox *mbox = dev_id;
> >> +	uint32_t status;
> >> +	int n;
> >> +
> >> +	/* Only examine channels that are currently enabled. */
> >> +	status = readl(mbox->regs + LOCAL_IRQ_EN_REG) &
> >> +		 readl(mbox->regs + LOCAL_IRQ_STAT_REG);
> >> +
> >> +	if (!(status & RX_IRQ_MASK))
> >> +		return IRQ_NONE;
> >> +
> >> +	for (n = 0; n < NUM_CHANS; ++n) {
> >> +		struct mbox_chan *chan = &mbox->controller.chans[n];
> >> +
> >> +		if (!(status & RX_IRQ(n)))
> >> +			continue;
> >> +
> >> +		while (sunxi_msgbox_peek_data(chan)) {
> >> +			uint32_t msg = readl(mbox->regs + MSG_DATA_REG(n));
> >> +
> >> +			mbox_dbg(mbox, "Channel %d received 0x%08x\n", n, msg);
> >> +			mbox_chan_received_data(chan, &msg);
> >> +		}
> >> +
> >> +		/* The IRQ can be cleared only once the FIFO is empty. */
> >> +		writel(RX_IRQ(n), mbox->regs + LOCAL_IRQ_STAT_REG);
> >> +	}
> >> +
> >> +	return IRQ_HANDLED;
> >> +}
> >> +
> >> +static int sunxi_msgbox_send_data(struct mbox_chan *chan, void *data)
> >> +{
> >> +	struct sunxi_msgbox *mbox = channel_to_msgbox(chan);
> >> +	int n = channel_number(chan);
> >> +	uint32_t msg = *(uint32_t *)data;
> >> +
> >> +	/* Using a channel backwards gets the hardware into a bad state. */
> >> +	if (WARN_ON_ONCE(!(readl(mbox->regs + CTRL_REG(n)) & CTRL_TX(n))))
> >> +		return 0;
> >> +
> >> +	/* We cannot post a new message if the FIFO is full. */
> >> +	if (readl(mbox->regs + FIFO_STAT_REG(n)) & FIFO_STAT_MASK) {
> >> +		mbox_dbg(mbox, "Channel %d busy sending 0x%08x\n", n, msg);
> >> +		return -EBUSY;
> >> +	}
> >> +
> >> +	writel(msg, mbox->regs + MSG_DATA_REG(n));
> >> +	mbox_dbg(mbox, "Channel %d sent 0x%08x\n", n, msg);
> >> +
> >> +	return 0;
> >> +}
> >> +
> >> +static int sunxi_msgbox_startup(struct mbox_chan *chan)
> >> +{
> >> +	struct sunxi_msgbox *mbox = channel_to_msgbox(chan);
> >> +	int n = channel_number(chan);
> >> +
> >> +	/* The coprocessor is responsible for setting channel directions. */
> >> +	if (readl(mbox->regs + CTRL_REG(n)) & CTRL_RX(n)) {
> >> +		/* Flush the receive FIFO. */
> >> +		while (sunxi_msgbox_peek_data(chan))
> >> +			readl(mbox->regs + MSG_DATA_REG(n));
> >> +		writel(RX_IRQ(n), mbox->regs + LOCAL_IRQ_STAT_REG);
> >> +
> >> +		/* Enable the receive IRQ. */
> >> +		spin_lock(&mbox->lock);
> >> +		writel(readl(mbox->regs + LOCAL_IRQ_EN_REG) | RX_IRQ(n),
> >> +		       mbox->regs + LOCAL_IRQ_EN_REG);
> >> +		spin_unlock(&mbox->lock);
> >> +	}
> >> +
> >> +	mbox_dbg(mbox, "Channel %d startup complete\n", n);
> >> +
> >> +	return 0;
> >> +}
> >> +
> >> +static void sunxi_msgbox_shutdown(struct mbox_chan *chan)
> >> +{
> >> +	struct sunxi_msgbox *mbox = channel_to_msgbox(chan);
> >> +	int n = channel_number(chan);
> >> +
> >> +	if (readl(mbox->regs + CTRL_REG(n)) & CTRL_RX(n)) {
> >> +		/* Disable the receive IRQ. */
> >> +		spin_lock(&mbox->lock);
> >> +		writel(readl(mbox->regs + LOCAL_IRQ_EN_REG) & ~RX_IRQ(n),
> >> +		       mbox->regs + LOCAL_IRQ_EN_REG);
> >> +		spin_unlock(&mbox->lock);
> >> +
> >> +		/* Attempt to flush the FIFO until the IRQ is cleared. */
> >> +		do {
> >> +			while (sunxi_msgbox_peek_data(chan))
> >> +				readl(mbox->regs + MSG_DATA_REG(n));
> >> +			writel(RX_IRQ(n), mbox->regs + LOCAL_IRQ_STAT_REG);
> >> +		} while (readl(mbox->regs + LOCAL_IRQ_STAT_REG) & RX_IRQ(n));
> >> +	}
> >> +
> >> +	mbox_dbg(mbox, "Channel %d shutdown complete\n", n);
> >> +}
> >> +
> >> +static bool sunxi_msgbox_last_tx_done(struct mbox_chan *chan)
> >> +{
> >> +	struct sunxi_msgbox *mbox = channel_to_msgbox(chan);
> >> +	int n = channel_number(chan);
> >> +
> >> +	/*
> >> +	 * The hardware allows snooping on the remote user's IRQ statuses.
> >> +	 * We consider a message to be acknowledged only once the receive IRQ
> >> +	 * for that channel is cleared. Since the receive IRQ for a channel
> >> +	 * cannot be cleared until the FIFO for that channel is empty, this
> >> +	 * ensures that the message has actually been read. It also gives the
> >> +	 * recipient an opportunity to perform minimal processing before
> >> +	 * acknowledging the message.
> >> +	 */
> >> +	return !(readl(mbox->regs + REMOTE_IRQ_STAT_REG) & RX_IRQ(n));
> >> +}
> >> +
> >> +static bool sunxi_msgbox_peek_data(struct mbox_chan *chan)
> >> +{
> >> +	struct sunxi_msgbox *mbox = channel_to_msgbox(chan);
> >> +	int n = channel_number(chan);
> >> +
> >> +	return readl(mbox->regs + MSG_STAT_REG(n)) & MSG_STAT_MASK;
> >> +}
> >> +
> >> +static const struct mbox_chan_ops sunxi_msgbox_chan_ops = {
> >> +	.send_data    = sunxi_msgbox_send_data,
> >> +	.startup      = sunxi_msgbox_startup,
> >> +	.shutdown     = sunxi_msgbox_shutdown,
> >> +	.last_tx_done = sunxi_msgbox_last_tx_done,
> >> +	.peek_data    = sunxi_msgbox_peek_data,
> >> +};
> >> +
> >> +static int sunxi_msgbox_probe(struct platform_device *pdev)
> >> +{
> >> +	struct device *dev = &pdev->dev;
> >> +	struct mbox_chan *chans;
> >> +	struct reset_control *reset;
> >> +	struct resource *res;
> >> +	struct sunxi_msgbox *mbox;
> >> +	int i, ret;
> >> +
> >> +	mbox = devm_kzalloc(dev, sizeof(*mbox), GFP_KERNEL);
> >> +	if (!mbox)
> >> +		return -ENOMEM;
> >> +
> >> +	chans = devm_kcalloc(dev, NUM_CHANS, sizeof(*chans), GFP_KERNEL);
> >> +	if (!chans)
> >> +		return -ENOMEM;
> >> +
> >> +	for (i = 0; i < NUM_CHANS; ++i)
> >> +		chans[i].con_priv = mbox;
> >> +
> >> +	mbox->clk = devm_clk_get(dev, NULL);
> >> +	if (IS_ERR(mbox->clk)) {
> >> +		ret = PTR_ERR(mbox->clk);
> >> +		dev_err(dev, "Failed to get clock: %d\n", ret);
> >> +		return ret;
> >> +	}
> >> +
> >> +	ret = clk_prepare_enable(mbox->clk);
> >> +	if (ret) {
> >> +		dev_err(dev, "Failed to enable clock: %d\n", ret);
> >> +		return ret;
> >> +	}
> >> +
> >> +	reset = devm_reset_control_get(dev, NULL);
> >> +	if (IS_ERR(reset)) {
> >> +		ret = PTR_ERR(reset);
> >> +		dev_err(dev, "Failed to get reset control: %d\n", ret);
> >> +		goto err_disable_unprepare;
> >> +	}
> >> +
> >> +	ret = reset_control_deassert(reset);
> >> +	if (ret) {
> >> +		dev_err(dev, "Failed to deassert reset: %d\n", ret);
> >> +		goto err_disable_unprepare;
> >> +	}
> > 
> > You need to assert the reset again from now on, in error paths. devm
> > will not do that for you.
> 
> I know, and that's intentional. This same message box device is used for ATF to
> communicate with SCP firmware (on a different channel). This could be happening
> on a different core while Linux is running. So Linux is not allowed to deassert
> the reset. clk_disable_unprepare() is only okay because the clock is marked as
> critical.

Okay. It needs to be docummented here though, so that someone will
not "fix" it in the future, after finding this with coccinelle or
something.

regards,
	o.

> >> +	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> >> +	if (!res) {
> >> +		ret = -ENODEV;
> >> +		goto err_disable_unprepare;
> >> +	}
> >> +
> >> +	mbox->regs = devm_ioremap_resource(&pdev->dev, res);
> >> +	if (IS_ERR(mbox->regs)) {
> >> +		ret = PTR_ERR(mbox->regs);
> >> +		dev_err(dev, "Failed to map MMIO resource: %d\n", ret);
> >> +		goto err_disable_unprepare;
> >> +	}
> >> +
> >> +	/* Disable all IRQs for this end of the msgbox. */
> >> +	writel(0, mbox->regs + LOCAL_IRQ_EN_REG);
> >> +
> >> +	ret = devm_request_irq(dev, irq_of_parse_and_map(dev->of_node, 0),
> >> +			       sunxi_msgbox_irq, 0, dev_name(dev), mbox);
> >> +	if (ret) {
> >> +		dev_err(dev, "Failed to register IRQ handler: %d\n", ret);
> >> +		goto err_disable_unprepare;
> >> +	}
> >> +
> >> +	mbox->controller.dev           = dev;
> >> +	mbox->controller.ops           = &sunxi_msgbox_chan_ops;
> >> +	mbox->controller.chans         = chans;
> >> +	mbox->controller.num_chans     = NUM_CHANS;
> >> +	mbox->controller.txdone_irq    = false;
> >> +	mbox->controller.txdone_poll   = true;
> >> +	mbox->controller.txpoll_period = 5;
> >> +
> >> +	spin_lock_init(&mbox->lock);
> >> +	platform_set_drvdata(pdev, mbox);
> >> +
> >> +	ret = mbox_controller_register(&mbox->controller);
> >> +	if (ret) {
> >> +		dev_err(dev, "Failed to register controller: %d\n", ret);
> >> +		goto err_disable_unprepare;
> >> +	}
> >> +
> >> +	return 0;
> >> +
> >> +err_disable_unprepare:
> >> +	clk_disable_unprepare(mbox->clk);
> >> +
> >> +	return ret;
> >> +}
> >> +
> >> +static int sunxi_msgbox_remove(struct platform_device *pdev)
> >> +{
> >> +	struct sunxi_msgbox *mbox = platform_get_drvdata(pdev);
> >> +
> >> +	mbox_controller_unregister(&mbox->controller);
> >> +	clk_disable_unprepare(mbox->clk);
> > 
> > Also, assert the reset here.
> 
> Same comment as above. This is intentional.
> 
> Thanks,
> Samuel
> 
> >> +	return 0;
> >> +}
> >> +
> >> +static const struct of_device_id sunxi_msgbox_of_match[] = {
> >> +	{ .compatible = "allwinner,sun6i-a31-msgbox", },
> >> +	{},
> >> +};
> >> +MODULE_DEVICE_TABLE(of, sunxi_msgbox_of_match);
> >> +
> >> +static struct platform_driver sunxi_msgbox_driver = {
> >> +	.driver = {
> >> +		.name = "sunxi-msgbox",
> >> +		.of_match_table = sunxi_msgbox_of_match,
> >> +	},
> >> +	.probe  = sunxi_msgbox_probe,
> >> +	.remove = sunxi_msgbox_remove,
> >> +};
> >> +module_platform_driver(sunxi_msgbox_driver);
> >> +
> >> +MODULE_AUTHOR("Samuel Holland <samuel@sholland.org>");
> >> +MODULE_DESCRIPTION("Allwinner sunxi Message Box");
> >> +MODULE_LICENSE("GPL v2");
> >> -- 
> >> 2.21.0
> 
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