[PATCH v5 0/2] serial: 8250_dw: optional reset control and deferred probe support

[PATCH v5 0/2] serial: 8250_dw: optional reset control and deferred probe support

[Chen-Yu Tsai]

Hi Greg,

This series adds optional reset control and deferred probing support
to 8250_dw. These are required to support the UARTs on sun6i/sun8i.
They were originally part of my sun8i PRCM series. The other parts
of that series have been merged already. It would be really nice
if we could get these 2 in as well.

Patch 1 adds optional reset control support to the 8250_dw, which
is used by sun6i and sun8i platforms. Till now, this wasn't needed
from a working standpoint, as the bootloader de-asserts the reset
control on the console UART for us. However, during the development
of the sun8i patches, I noticed other UARTs wouldn't work. Also the
new sun6i A31 Hummingbird has multiple UARTs available, which would
require this patch.

Patch 2 adds deferred probing to 8250_dw. In my case, even though
the clocks and reset controller "devices" were registered before
the UART, the 8250_dw driver binded with the UART devices before
the clocks and resets were available. This resulted in the 8250_dw
driver failing. I only tested the R_UART device.

Patch 2 also does proper cleanup in the event that probing failed.

Maxime, I dropped your Acked-by because I added the cleanup code
path.

Changes since v4:
  - Rebased onto tty-next (4847914)
  - Do proper cleanup in the probe function if errors are encountered.

No changes before v4.


Cheers
ChenYu


Chen-Yu Tsai (2):
  serial: 8250_dw: Add optional reset control support
  serial: 8250_dw: Add support for deferred probing

 .../bindings/serial/snps-dw-apb-uart.txt           |  1 +
 drivers/tty/serial/8250/8250_dw.c                  | 50 +++++++++++++++++++---
 2 files changed, 44 insertions(+), 7 deletions(-)

-- 
2.0.1

[PATCH v5 0/2] serial: 8250_dw: optional reset control and deferred probe support

[Chen-Yu Tsai]

Hi Greg,

This series adds optional reset control and deferred probing support
to 8250_dw. These are required to support the UARTs on sun6i/sun8i.
They were originally part of my sun8i PRCM series. The other parts
of that series have been merged already. It would be really nice
if we could get these 2 in as well.

Patch 1 adds optional reset control support to the 8250_dw, which
is used by sun6i and sun8i platforms. Till now, this wasn't needed
from a working standpoint, as the bootloader de-asserts the reset
control on the console UART for us. However, during the development
of the sun8i patches, I noticed other UARTs wouldn't work. Also the
new sun6i A31 Hummingbird has multiple UARTs available, which would
require this patch.

Patch 2 adds deferred probing to 8250_dw. In my case, even though
the clocks and reset controller "devices" were registered before
the UART, the 8250_dw driver binded with the UART devices before
the clocks and resets were available. This resulted in the 8250_dw
driver failing. I only tested the R_UART device.

Patch 2 also does proper cleanup in the event that probing failed.

Maxime, I dropped your Acked-by because I added the cleanup code
path.

Changes since v4:
  - Rebased onto tty-next (4847914)
  - Do proper cleanup in the probe function if errors are encountered.

No changes before v4.


Cheers
ChenYu


Chen-Yu Tsai (2):
  serial: 8250_dw: Add optional reset control support
  serial: 8250_dw: Add support for deferred probing

 .../bindings/serial/snps-dw-apb-uart.txt           |  1 +
 drivers/tty/serial/8250/8250_dw.c                  | 50 +++++++++++++++++++---
 2 files changed, 44 insertions(+), 7 deletions(-)

-- 
2.0.1

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[PATCH v5 0/2] serial: 8250_dw: optional reset control and deferred probe support

[Chen-Yu Tsai]

Hi Greg,

This series adds optional reset control and deferred probing support
to 8250_dw. These are required to support the UARTs on sun6i/sun8i.
They were originally part of my sun8i PRCM series. The other parts
of that series have been merged already. It would be really nice
if we could get these 2 in as well.

Patch 1 adds optional reset control support to the 8250_dw, which
is used by sun6i and sun8i platforms. Till now, this wasn't needed
from a working standpoint, as the bootloader de-asserts the reset
control on the console UART for us. However, during the development
of the sun8i patches, I noticed other UARTs wouldn't work. Also the
new sun6i A31 Hummingbird has multiple UARTs available, which would
require this patch.

Patch 2 adds deferred probing to 8250_dw. In my case, even though
the clocks and reset controller "devices" were registered before
the UART, the 8250_dw driver binded with the UART devices before
the clocks and resets were available. This resulted in the 8250_dw
driver failing. I only tested the R_UART device.

Patch 2 also does proper cleanup in the event that probing failed.

Maxime, I dropped your Acked-by because I added the cleanup code
path.

Changes since v4:
  - Rebased onto tty-next (4847914)
  - Do proper cleanup in the probe function if errors are encountered.

No changes before v4.


Cheers
ChenYu


Chen-Yu Tsai (2):
  serial: 8250_dw: Add optional reset control support
  serial: 8250_dw: Add support for deferred probing

 .../bindings/serial/snps-dw-apb-uart.txt           |  1 +
 drivers/tty/serial/8250/8250_dw.c                  | 50 +++++++++++++++++++---
 2 files changed, 44 insertions(+), 7 deletions(-)

-- 
2.0.1

[PATCH v5 1/2] serial: 8250_dw: Add optional reset control support

[Chen-Yu Tsai]

The Allwinner A31 and A23 SoCs have a reset controller
maintaining the UART in reset by default.

This patch adds optional reset support to the driver.

Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Acked-by: Maxime Ripard <maxime.ripard@free-electrons.com>
---
 Documentation/devicetree/bindings/serial/snps-dw-apb-uart.txt | 1 +
 drivers/tty/serial/8250/8250_dw.c                             | 9 +++++++++
 2 files changed, 10 insertions(+)

diff --git a/Documentation/devicetree/bindings/serial/snps-dw-apb-uart.txt b/Documentation/devicetree/bindings/serial/snps-dw-apb-uart.txt
index 095ac71..7f76214 100644
--- a/Documentation/devicetree/bindings/serial/snps-dw-apb-uart.txt
+++ b/Documentation/devicetree/bindings/serial/snps-dw-apb-uart.txt
@@ -15,6 +15,7 @@ The supplying peripheral clock can also be handled, needing a second property
 	Required elements: "baudclk", "apb_pclk"
 
 Optional properties:
+- resets : phandle to the parent reset controller.
 - reg-shift : quantity to shift the register offsets by.  If this property is
   not present then the register offsets are not shifted.
 - reg-io-width : the size (in bytes) of the IO accesses that should be
diff --git a/drivers/tty/serial/8250/8250_dw.c b/drivers/tty/serial/8250/8250_dw.c
index affdcb1..501db2f 100644
--- a/drivers/tty/serial/8250/8250_dw.c
+++ b/drivers/tty/serial/8250/8250_dw.c
@@ -26,6 +26,7 @@
 #include <linux/slab.h>
 #include <linux/acpi.h>
 #include <linux/clk.h>
+#include <linux/reset.h>
 #include <linux/pm_runtime.h>
 
 #include <asm/byteorder.h>
@@ -60,6 +61,7 @@ struct dw8250_data {
 	int			line;
 	struct clk		*clk;
 	struct clk		*pclk;
+	struct reset_control	*rst;
 	struct uart_8250_dma	dma;
 };
 
@@ -383,6 +385,10 @@ static int dw8250_probe(struct platform_device *pdev)
 		}
 	}
 
+	data->rst = devm_reset_control_get_optional(&pdev->dev, NULL);
+	if (!IS_ERR(data->rst))
+		reset_control_deassert(data->rst);
+
 	data->dma.rx_chan_id = -1;
 	data->dma.tx_chan_id = -1;
 	data->dma.rx_param = data;
@@ -426,6 +432,9 @@ static int dw8250_remove(struct platform_device *pdev)
 
 	serial8250_unregister_port(data->line);
 
+	if (!IS_ERR(data->rst))
+		reset_control_assert(data->rst);
+
 	if (!IS_ERR(data->pclk))
 		clk_disable_unprepare(data->pclk);
 
-- 
2.0.1

[PATCH v5 1/2] serial: 8250_dw: Add optional reset control support

[Chen-Yu Tsai]

The Allwinner A31 and A23 SoCs have a reset controller
maintaining the UART in reset by default.

This patch adds optional reset support to the driver.

Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Acked-by: Maxime Ripard <maxime.ripard@free-electrons.com>
---
 Documentation/devicetree/bindings/serial/snps-dw-apb-uart.txt | 1 +
 drivers/tty/serial/8250/8250_dw.c                             | 9 +++++++++
 2 files changed, 10 insertions(+)

diff --git a/Documentation/devicetree/bindings/serial/snps-dw-apb-uart.txt b/Documentation/devicetree/bindings/serial/snps-dw-apb-uart.txt
index 095ac71..7f76214 100644
--- a/Documentation/devicetree/bindings/serial/snps-dw-apb-uart.txt
+++ b/Documentation/devicetree/bindings/serial/snps-dw-apb-uart.txt
@@ -15,6 +15,7 @@ The supplying peripheral clock can also be handled, needing a second property
 	Required elements: "baudclk", "apb_pclk"
 
 Optional properties:
+- resets : phandle to the parent reset controller.
 - reg-shift : quantity to shift the register offsets by.  If this property is
   not present then the register offsets are not shifted.
 - reg-io-width : the size (in bytes) of the IO accesses that should be
diff --git a/drivers/tty/serial/8250/8250_dw.c b/drivers/tty/serial/8250/8250_dw.c
index affdcb1..501db2f 100644
--- a/drivers/tty/serial/8250/8250_dw.c
+++ b/drivers/tty/serial/8250/8250_dw.c
@@ -26,6 +26,7 @@
 #include <linux/slab.h>
 #include <linux/acpi.h>
 #include <linux/clk.h>
+#include <linux/reset.h>
 #include <linux/pm_runtime.h>
 
 #include <asm/byteorder.h>
@@ -60,6 +61,7 @@ struct dw8250_data {
 	int			line;
 	struct clk		*clk;
 	struct clk		*pclk;
+	struct reset_control	*rst;
 	struct uart_8250_dma	dma;
 };
 
@@ -383,6 +385,10 @@ static int dw8250_probe(struct platform_device *pdev)
 		}
 	}
 
+	data->rst = devm_reset_control_get_optional(&pdev->dev, NULL);
+	if (!IS_ERR(data->rst))
+		reset_control_deassert(data->rst);
+
 	data->dma.rx_chan_id = -1;
 	data->dma.tx_chan_id = -1;
 	data->dma.rx_param = data;
@@ -426,6 +432,9 @@ static int dw8250_remove(struct platform_device *pdev)
 
 	serial8250_unregister_port(data->line);
 
+	if (!IS_ERR(data->rst))
+		reset_control_assert(data->rst);
+
 	if (!IS_ERR(data->pclk))
 		clk_disable_unprepare(data->pclk);
 
-- 
2.0.1

[PATCH v5 2/2] serial: 8250_dw: Add support for deferred probing

[Chen-Yu Tsai]

The 8250_dw driver fails to probe if the specified clock isn't
registered at probe time. Even if a clock frequency is given,
the required clock might be gated because it wasn't properly
enabled.

This happened to me when the device is registered through DT,
and the clock was part of an MFD, the PRCM found on A31 and A23
SoCs. Unlike core clocks that are registered with OF_CLK_DECLARE,
which happen almost immediately after the kernel starts, the
clocks are registered as sub-devices of the PRCM MFD platform
device. Even though devices are registered in the order they are
found in the DT, the drivers are registered in a different,
arbitrary order. It is possible that the 8250_dw driver is
registered, and thus associated with the device and probed, before
the clock driver is registered and probed.

8250_dw then reports unable to get the clock, and fails. Without
a working console, the kernel panics.

This patch adds support for deferred probe handling for the clock
and reset controller. It also fixes the cleanup path if
serial8250_register_8250_port fails.

Signed-off-by: Chen-Yu Tsai <wens@csie.org>
---
 drivers/tty/serial/8250/8250_dw.c | 41 ++++++++++++++++++++++++++++++++-------
 1 file changed, 34 insertions(+), 7 deletions(-)

diff --git a/drivers/tty/serial/8250/8250_dw.c b/drivers/tty/serial/8250/8250_dw.c
index 501db2f..4db7987 100644
--- a/drivers/tty/serial/8250/8250_dw.c
+++ b/drivers/tty/serial/8250/8250_dw.c
@@ -365,8 +365,10 @@ static int dw8250_probe(struct platform_device *pdev)
 
 	data->usr_reg = DW_UART_USR;
 	data->clk = devm_clk_get(&pdev->dev, "baudclk");
-	if (IS_ERR(data->clk))
+	if (IS_ERR(data->clk) && PTR_ERR(data->clk) != -EPROBE_DEFER)
 		data->clk = devm_clk_get(&pdev->dev, NULL);
+	if (IS_ERR(data->clk) && PTR_ERR(data->clk) == -EPROBE_DEFER)
+		return -EPROBE_DEFER;
 	if (!IS_ERR(data->clk)) {
 		err = clk_prepare_enable(data->clk);
 		if (err)
@@ -377,15 +379,23 @@ static int dw8250_probe(struct platform_device *pdev)
 	}
 
 	data->pclk = devm_clk_get(&pdev->dev, "apb_pclk");
+	if (IS_ERR(data->clk) && PTR_ERR(data->clk) == -EPROBE_DEFER) {
+		err = -EPROBE_DEFER;
+		goto err_clk;
+	}
 	if (!IS_ERR(data->pclk)) {
 		err = clk_prepare_enable(data->pclk);
 		if (err) {
 			dev_err(&pdev->dev, "could not enable apb_pclk\n");
-			return err;
+			goto err_clk;
 		}
 	}
 
 	data->rst = devm_reset_control_get_optional(&pdev->dev, NULL);
+	if (IS_ERR(data->rst) && PTR_ERR(data->rst) == -EPROBE_DEFER) {
+		err = -EPROBE_DEFER;
+		goto err_pclk;
+	}
 	if (!IS_ERR(data->rst))
 		reset_control_deassert(data->rst);
 
@@ -403,18 +413,21 @@ static int dw8250_probe(struct platform_device *pdev)
 	if (pdev->dev.of_node) {
 		err = dw8250_probe_of(&uart.port, data);
 		if (err)
-			return err;
+			goto err_reset;
 	} else if (ACPI_HANDLE(&pdev->dev)) {
 		err = dw8250_probe_acpi(&uart, data);
 		if (err)
-			return err;
+			goto err_reset;
 	} else {
-		return -ENODEV;
+		err = -ENODEV;
+		goto err_reset;
 	}
 
 	data->line = serial8250_register_8250_port(&uart);
-	if (data->line < 0)
-		return data->line;
+	if (data->line < 0) {
+		err = data->line;
+		goto err_reset;
+	}
 
 	platform_set_drvdata(pdev, data);
 
@@ -422,6 +435,20 @@ static int dw8250_probe(struct platform_device *pdev)
 	pm_runtime_enable(&pdev->dev);
 
 	return 0;
+
+err_reset:
+	if (!IS_ERR(data->rst))
+		reset_control_assert(data->rst);
+
+err_pclk:
+	if (!IS_ERR(data->pclk))
+		clk_disable_unprepare(data->pclk);
+
+err_clk:
+	if (!IS_ERR(data->clk))
+		clk_disable_unprepare(data->clk);
+
+	return err;
 }
 
 static int dw8250_remove(struct platform_device *pdev)
-- 
2.0.1

[PATCH v5 2/2] serial: 8250_dw: Add support for deferred probing

[Chen-Yu Tsai]

The 8250_dw driver fails to probe if the specified clock isn't
registered at probe time. Even if a clock frequency is given,
the required clock might be gated because it wasn't properly
enabled.

This happened to me when the device is registered through DT,
and the clock was part of an MFD, the PRCM found on A31 and A23
SoCs. Unlike core clocks that are registered with OF_CLK_DECLARE,
which happen almost immediately after the kernel starts, the
clocks are registered as sub-devices of the PRCM MFD platform
device. Even though devices are registered in the order they are
found in the DT, the drivers are registered in a different,
arbitrary order. It is possible that the 8250_dw driver is
registered, and thus associated with the device and probed, before
the clock driver is registered and probed.

8250_dw then reports unable to get the clock, and fails. Without
a working console, the kernel panics.

This patch adds support for deferred probe handling for the clock
and reset controller. It also fixes the cleanup path if
serial8250_register_8250_port fails.

Signed-off-by: Chen-Yu Tsai <wens@csie.org>
---
 drivers/tty/serial/8250/8250_dw.c | 41 ++++++++++++++++++++++++++++++++-------
 1 file changed, 34 insertions(+), 7 deletions(-)

diff --git a/drivers/tty/serial/8250/8250_dw.c b/drivers/tty/serial/8250/8250_dw.c
index 501db2f..4db7987 100644
--- a/drivers/tty/serial/8250/8250_dw.c
+++ b/drivers/tty/serial/8250/8250_dw.c
@@ -365,8 +365,10 @@ static int dw8250_probe(struct platform_device *pdev)
 
 	data->usr_reg = DW_UART_USR;
 	data->clk = devm_clk_get(&pdev->dev, "baudclk");
-	if (IS_ERR(data->clk))
+	if (IS_ERR(data->clk) && PTR_ERR(data->clk) != -EPROBE_DEFER)
 		data->clk = devm_clk_get(&pdev->dev, NULL);
+	if (IS_ERR(data->clk) && PTR_ERR(data->clk) == -EPROBE_DEFER)
+		return -EPROBE_DEFER;
 	if (!IS_ERR(data->clk)) {
 		err = clk_prepare_enable(data->clk);
 		if (err)
@@ -377,15 +379,23 @@ static int dw8250_probe(struct platform_device *pdev)
 	}
 
 	data->pclk = devm_clk_get(&pdev->dev, "apb_pclk");
+	if (IS_ERR(data->clk) && PTR_ERR(data->clk) == -EPROBE_DEFER) {
+		err = -EPROBE_DEFER;
+		goto err_clk;
+	}
 	if (!IS_ERR(data->pclk)) {
 		err = clk_prepare_enable(data->pclk);
 		if (err) {
 			dev_err(&pdev->dev, "could not enable apb_pclk\n");
-			return err;
+			goto err_clk;
 		}
 	}
 
 	data->rst = devm_reset_control_get_optional(&pdev->dev, NULL);
+	if (IS_ERR(data->rst) && PTR_ERR(data->rst) == -EPROBE_DEFER) {
+		err = -EPROBE_DEFER;
+		goto err_pclk;
+	}
 	if (!IS_ERR(data->rst))
 		reset_control_deassert(data->rst);
 
@@ -403,18 +413,21 @@ static int dw8250_probe(struct platform_device *pdev)
 	if (pdev->dev.of_node) {
 		err = dw8250_probe_of(&uart.port, data);
 		if (err)
-			return err;
+			goto err_reset;
 	} else if (ACPI_HANDLE(&pdev->dev)) {
 		err = dw8250_probe_acpi(&uart, data);
 		if (err)
-			return err;
+			goto err_reset;
 	} else {
-		return -ENODEV;
+		err = -ENODEV;
+		goto err_reset;
 	}
 
 	data->line = serial8250_register_8250_port(&uart);
-	if (data->line < 0)
-		return data->line;
+	if (data->line < 0) {
+		err = data->line;
+		goto err_reset;
+	}
 
 	platform_set_drvdata(pdev, data);
 
@@ -422,6 +435,20 @@ static int dw8250_probe(struct platform_device *pdev)
 	pm_runtime_enable(&pdev->dev);
 
 	return 0;
+
+err_reset:
+	if (!IS_ERR(data->rst))
+		reset_control_assert(data->rst);
+
+err_pclk:
+	if (!IS_ERR(data->pclk))
+		clk_disable_unprepare(data->pclk);
+
+err_clk:
+	if (!IS_ERR(data->clk))
+		clk_disable_unprepare(data->clk);
+
+	return err;
 }
 
 static int dw8250_remove(struct platform_device *pdev)
-- 
2.0.1