i2c: tegra: Support atomic transfers

System shutdown may happen with interrupts being disabled and in this case
kernel may hang if atomic transfer isn't supported by driver.

There were several occurrences where I found my Nexus 7 completely
discharged despite of being turned off and then one day I spotted this in
the log:

 reboot: Power down
 ------------[ cut here ]------------
 WARNING: CPU: 0 PID: 1 at drivers/i2c/i2c-core.h:40 i2c_transfer+0x95/0x9c
 No atomic I2C transfer handler for 'i2c-1'
 Modules linked in: tegra30_devfreq
 CPU: 0 PID: 1 Comm: systemd-shutdow Not tainted 5.4.0-next-20191202-00120-gf7ecd80fb803-dirty #3195
 Hardware name: NVIDIA Tegra SoC (Flattened Device Tree)
 [<c010e4b5>] (unwind_backtrace) from [<c010a0fd>] (show_stack+0x11/0x14)
 [<c010a0fd>] (show_stack) from [<c09995e5>] (dump_stack+0x85/0x94)
 [<c09995e5>] (dump_stack) from [<c011f3d1>] (__warn+0xc1/0xc4)
 [<c011f3d1>] (__warn) from [<c011f691>] (warn_slowpath_fmt+0x61/0x78)
 [<c011f691>] (warn_slowpath_fmt) from [<c069a8dd>] (i2c_transfer+0x95/0x9c)
 [<c069a8dd>] (i2c_transfer) from [<c05667f1>] (regmap_i2c_read+0x4d/0x6c)
 [<c05667f1>] (regmap_i2c_read) from [<c0563601>] (_regmap_raw_read+0x99/0x1cc)
 [<c0563601>] (_regmap_raw_read) from [<c0563757>] (_regmap_bus_read+0x23/0x38)
 [<c0563757>] (_regmap_bus_read) from [<c056293d>] (_regmap_read+0x3d/0xfc)
 [<c056293d>] (_regmap_read) from [<c0562d3b>] (_regmap_update_bits+0x87/0xc4)
 [<c0562d3b>] (_regmap_update_bits) from [<c0563add>] (regmap_update_bits_base+0x39/0x50)
 [<c0563add>] (regmap_update_bits_base) from [<c056fd39>] (max77620_pm_power_off+0x29/0x2c)
 [<c056fd39>] (max77620_pm_power_off) from [<c013bbdd>] (__do_sys_reboot+0xe9/0x170)
 [<c013bbdd>] (__do_sys_reboot) from [<c0101001>] (ret_fast_syscall+0x1/0x28)
 Exception stack(0xde907fa8 to 0xde907ff0)
 7fa0:                   00000000 00000000 fee1dead 28121969 4321fedc 00000000
 7fc0: 00000000 00000000 00000000 00000058 00000000 00000000 00000000 00000000
 7fe0: 0045adf0 bed9abb8 004444a0 b6c666d0
 ---[ end trace bdd18f87595b1a5e ]---

The atomic transferring is implemented by enforcing PIO mode for the
transfer and by polling interrupt status until transfer is completed or
failed.

Now system shuts down properly every time.
Tested-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>

drivers/i2c/busses/i2c-tegra.c

@@ -18,6 +18,7 @@
 #include <linux/iopoll.h>
 #include <linux/irq.h>
 #include <linux/kernel.h>
+#include <linux/ktime.h>
 #include <linux/module.h>
 #include <linux/of_device.h>
 #include <linux/pinctrl/consumer.h>
@@ -247,6 +248,7 @@ struct tegra_i2c_hw_feature {
  * @dma_buf_size: DMA buffer size
  * @is_curr_dma_xfer: indicates active DMA transfer
  * @dma_complete: DMA completion notifier
+ * @is_curr_atomic_xfer: indicates active atomic transfer
  */
 struct tegra_i2c_dev {
 	struct device *dev;
@@ -275,6 +277,7 @@ struct tegra_i2c_dev {
 	unsigned int dma_buf_size;
 	bool is_curr_dma_xfer;
 	struct completion dma_complete;
+	bool is_curr_atomic_xfer;
 };
 
 static void dvc_writel(struct tegra_i2c_dev *i2c_dev, u32 val,
@@ -683,7 +686,8 @@ static int tegra_i2c_wait_for_config_load(struct tegra_i2c_dev *i2c_dev)
 		reg_offset = tegra_i2c_reg_addr(i2c_dev, I2C_CONFIG_LOAD);
 		addr = i2c_dev->base + reg_offset;
 		i2c_writel(i2c_dev, I2C_MSTR_CONFIG_LOAD, I2C_CONFIG_LOAD);
-		if (in_interrupt())
+
+		if (i2c_dev->is_curr_atomic_xfer)
 			err = readl_poll_timeout_atomic(addr, val, val == 0,
 							1000,
 							I2C_CONFIG_LOAD_TIMEOUT);
@@ -983,6 +987,34 @@ static void tegra_i2c_config_fifo_trig(struct tegra_i2c_dev *i2c_dev,
 	i2c_writel(i2c_dev, val, reg);
 }
 
+static unsigned long
+tegra_i2c_poll_completion_timeout(struct tegra_i2c_dev *i2c_dev,
+				  struct completion *complete,
+				  unsigned int timeout_ms)
+{
+	ktime_t ktime = ktime_get();
+	ktime_t ktimeout = ktime_add_ms(ktime, timeout_ms);
+
+	do {
+		u32 status = i2c_readl(i2c_dev, I2C_INT_STATUS);
+
+		if (status) {
+			tegra_i2c_isr(i2c_dev->irq, i2c_dev);
+
+			if (completion_done(complete)) {
+				s64 delta = ktime_ms_delta(ktimeout, ktime);
+
+				return msecs_to_jiffies(delta) ?: 1;
+			}
+		}
+
+		ktime = ktime_get();
+
+	} while (ktime_before(ktime, ktimeout));
+
+	return 0;
+}
+
 static unsigned long
 tegra_i2c_wait_completion_timeout(struct tegra_i2c_dev *i2c_dev,
 				  struct completion *complete,
@@ -990,18 +1022,24 @@ tegra_i2c_wait_completion_timeout(struct tegra_i2c_dev *i2c_dev,
 {
 	unsigned long ret;
 
-	enable_irq(i2c_dev->irq);
-	ret = wait_for_completion_timeout(complete,
-					  msecs_to_jiffies(timeout_ms));
-	disable_irq(i2c_dev->irq);
+	if (i2c_dev->is_curr_atomic_xfer) {
+		ret = tegra_i2c_poll_completion_timeout(i2c_dev, complete,
+							timeout_ms);
+	} else {
+		enable_irq(i2c_dev->irq);
+		ret = wait_for_completion_timeout(complete,
+						  msecs_to_jiffies(timeout_ms));
+		disable_irq(i2c_dev->irq);
 
-	/*
-	 * There is a chance that completion may happen after IRQ
-	 * synchronization, which is done by disable_irq().
-	 */
-	if (ret == 0 && completion_done(complete)) {
-		dev_warn(i2c_dev->dev, "completion done after timeout\n");
-		ret = 1;
+		/*
+		 * There is a chance that completion may happen after IRQ
+		 * synchronization, which is done by disable_irq().
+		 */
+		if (ret == 0 && completion_done(complete)) {
+			dev_warn(i2c_dev->dev,
+				 "completion done after timeout\n");
+			ret = 1;
+		}
 	}
 
 	return ret;
@@ -1073,7 +1111,8 @@ static int tegra_i2c_xfer_msg(struct tegra_i2c_dev *i2c_dev,
 
 	xfer_size = ALIGN(xfer_size, BYTES_PER_FIFO_WORD);
 	i2c_dev->is_curr_dma_xfer = (xfer_size > I2C_PIO_MODE_MAX_LEN) &&
-				    i2c_dev->dma_buf;
+				    i2c_dev->dma_buf &&
+				    !i2c_dev->is_curr_atomic_xfer;
 	tegra_i2c_config_fifo_trig(i2c_dev, xfer_size);
 	dma = i2c_dev->is_curr_dma_xfer;
 	/*
@@ -1271,6 +1310,19 @@ static int tegra_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg msgs[],
 	return ret ?: i;
 }
 
+static int tegra_i2c_xfer_atomic(struct i2c_adapter *adap,
+				 struct i2c_msg msgs[], int num)
+{
+	struct tegra_i2c_dev *i2c_dev = i2c_get_adapdata(adap);
+	int ret;
+
+	i2c_dev->is_curr_atomic_xfer = true;
+	ret = tegra_i2c_xfer(adap, msgs, num);
+	i2c_dev->is_curr_atomic_xfer = false;
+
+	return ret;
+}
+
 static u32 tegra_i2c_func(struct i2c_adapter *adap)
 {
 	struct tegra_i2c_dev *i2c_dev = i2c_get_adapdata(adap);
@@ -1298,8 +1350,9 @@ static void tegra_i2c_parse_dt(struct tegra_i2c_dev *i2c_dev)
 }
 
 static const struct i2c_algorithm tegra_i2c_algo = {
-	.master_xfer	= tegra_i2c_xfer,
-	.functionality	= tegra_i2c_func,
+	.master_xfer		= tegra_i2c_xfer,
+	.master_xfer_atomic	= tegra_i2c_xfer_atomic,
+	.functionality		= tegra_i2c_func,
 };
 
 /* payload size is only 12 bit */
@@ -1607,6 +1660,7 @@ static int tegra_i2c_probe(struct platform_device *pdev)
 		goto unprepare_fast_clk;
 	}
 
+	pm_runtime_irq_safe(&pdev->dev);
 	pm_runtime_enable(&pdev->dev);
 	if (!pm_runtime_enabled(&pdev->dev)) {
 		ret = tegra_i2c_runtime_resume(&pdev->dev);