[PATCH 0/3] i2c: xiic: Support forcing single-master in DT

[PATCH 0/3] i2c: xiic: Support forcing single-master in DT

[ext-jaakko.laine]

From: Jaakko Laine <ext-jaakko.laine@vaisala.com>

This patch series allows xiic driver to take advantage of
single-master -tag in device tree to improve reliability.

Changes from V2 review based on comments:
- Improved xiic_i2c struct memory alignment
- Simplify bus is busy checking code in single-master mode

Link to V2 review
https://www.spinics.net/lists/arm-kernel/msg831068.html

Jaakko Laine (3):
  i2c: xiic: Change code alignment to 1 space only
  i2c: xiic: Improve struct memory alignment
  i2c: xiic: Support forcing single-master in DT

 drivers/i2c/busses/i2c-xiic.c | 62 +++++++++++++++++++++--------------
 1 file changed, 38 insertions(+), 24 deletions(-)

-- 
2.19.1


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[PATCH 1/3] i2c: xiic: Change code alignment to 1 space only

[ext-jaakko.laine]

From: Jaakko Laine <ext-jaakko.laine@vaisala.com>

Alignment removed and replaced with 1 space only to
reduce need for future alignment changes affecting multiple
lines, when new variables are added.

Signed-off-by: Jaakko Laine <ext-jaakko.laine@vaisala.com>
Acked-by: Michal Simek <michal.simek@xilinx.com>
---
 drivers/i2c/busses/i2c-xiic.c | 48 +++++++++++++++++------------------
 1 file changed, 24 insertions(+), 24 deletions(-)

diff --git a/drivers/i2c/busses/i2c-xiic.c b/drivers/i2c/busses/i2c-xiic.c
index 90c1c362394d..10380531d45c 100644
--- a/drivers/i2c/busses/i2c-xiic.c
+++ b/drivers/i2c/busses/i2c-xiic.c
@@ -46,33 +46,33 @@ enum xiic_endian {
 
 /**
  * struct xiic_i2c - Internal representation of the XIIC I2C bus
- * @dev:	Pointer to device structure
- * @base:	Memory base of the HW registers
- * @wait:	Wait queue for callers
- * @adap:	Kernel adapter representation
- * @tx_msg:	Messages from above to be sent
- * @lock:	Mutual exclusion
- * @tx_pos:	Current pos in TX message
- * @nmsgs:	Number of messages in tx_msg
- * @state:	See STATE_
- * @rx_msg:	Current RX message
- * @rx_pos:	Position within current RX message
+ * @dev: Pointer to device structure
+ * @base: Memory base of the HW registers
+ * @wait: Wait queue for callers
+ * @adap: Kernel adapter representation
+ * @tx_msg: Messages from above to be sent
+ * @lock: Mutual exclusion
+ * @tx_pos: Current pos in TX message
+ * @nmsgs: Number of messages in tx_msg
+ * @state: See STATE_
+ * @rx_msg: Current RX message
+ * @rx_pos: Position within current RX message
  * @endianness: big/little-endian byte order
- * @clk:	Pointer to AXI4-lite input clock
+ * @clk: Pointer to AXI4-lite input clock
  */
 struct xiic_i2c {
-	struct device		*dev;
-	void __iomem		*base;
-	wait_queue_head_t	wait;
-	struct i2c_adapter	adap;
-	struct i2c_msg		*tx_msg;
-	struct mutex		lock;
-	unsigned int		tx_pos;
-	unsigned int		nmsgs;
-	enum xilinx_i2c_state	state;
-	struct i2c_msg		*rx_msg;
-	int			rx_pos;
-	enum xiic_endian	endianness;
+	struct device *dev;
+	void __iomem *base;
+	wait_queue_head_t wait;
+	struct i2c_adapter adap;
+	struct i2c_msg *tx_msg;
+	struct mutex lock;
+	unsigned int tx_pos;
+	unsigned int nmsgs;
+	enum xilinx_i2c_state state;
+	struct i2c_msg *rx_msg;
+	int rx_pos;
+	enum xiic_endian endianness;
 	struct clk *clk;
 };
 
-- 
2.19.1


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[PATCH 2/3] i2c: xiic: Improve struct memory alignment

[ext-jaakko.laine]

From: Jaakko Laine <ext-jaakko.laine@vaisala.com>

xiic_i2c struct alignment causes the struct to
take more space in memory than strictly required.
Move state -member to end of struct to get less
padding.

Signed-off-by: Jaakko Laine <ext-jaakko.laine@vaisala.com>
Suggested-by: Michal Simek <michal.simek@xilinx.com>
---
 drivers/i2c/busses/i2c-xiic.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/i2c/busses/i2c-xiic.c b/drivers/i2c/busses/i2c-xiic.c
index 10380531d45c..1453d82bb664 100644
--- a/drivers/i2c/busses/i2c-xiic.c
+++ b/drivers/i2c/busses/i2c-xiic.c
@@ -54,11 +54,11 @@ enum xiic_endian {
  * @lock: Mutual exclusion
  * @tx_pos: Current pos in TX message
  * @nmsgs: Number of messages in tx_msg
- * @state: See STATE_
  * @rx_msg: Current RX message
  * @rx_pos: Position within current RX message
  * @endianness: big/little-endian byte order
  * @clk: Pointer to AXI4-lite input clock
+ * @state: See STATE_
  */
 struct xiic_i2c {
 	struct device *dev;
@@ -69,11 +69,11 @@ struct xiic_i2c {
 	struct mutex lock;
 	unsigned int tx_pos;
 	unsigned int nmsgs;
-	enum xilinx_i2c_state state;
 	struct i2c_msg *rx_msg;
 	int rx_pos;
 	enum xiic_endian endianness;
 	struct clk *clk;
+	enum xilinx_i2c_state state;
 };
 
 
-- 
2.19.1


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[PATCH 3/3] i2c: xiic: Support forcing single-master in DT

[ext-jaakko.laine]

From: Jaakko Laine <ext-jaakko.laine@vaisala.com>

I2C master operating in multimaster mode can get stuck
indefinitely if I2C start is detected on bus, but no master
has a transaction going.

This is a weakness in I2C standard, which defines no way
to recover, since all masters are indefinitely disallowed
from interrupting the currently operating master. A start
condition can be created for example by an electromagnetic
discharge applied near physical I2C lines. Or a already
operating master could get reset immediately after sending
a start.

If it is known during device tree creation that only a single
I2C master will be present on the bus, this deadlock of the
I2C bus could be avoided in the driver by ignoring the
bus_is_busy register of the xiic, since bus can never be
reserved by any other master.

This patch adds this support for detecting single-master flag
in device tree and when provided, improves I2C reliability by
ignoring the therefore unnecessary xiic bus_is_busy register.

Error can be reproduced by pulling I2C SDA -line temporarily low
by shorting it to ground, while linux I2C master is operating on
it using the xiic driver. The application using the bus will
start receiving linux error code 16: "Device or resource busy"
indefinitely:

kernel: pca953x 0-0020: failed writing register
app: Error writing file, error: 16

With multi-master disabled device will instead receive error
code 5: "I/O error" while SDA is grounded, but recover normal
operation once short is removed.

kernel: pca953x 0-0020: failed reading register
app: Error reading file, error: 5

Signed-off-by: Jaakko Laine <ext-jaakko.laine@vaisala.com>
---
 drivers/i2c/busses/i2c-xiic.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/drivers/i2c/busses/i2c-xiic.c b/drivers/i2c/busses/i2c-xiic.c
index 1453d82bb664..087b2951942e 100644
--- a/drivers/i2c/busses/i2c-xiic.c
+++ b/drivers/i2c/busses/i2c-xiic.c
@@ -59,6 +59,7 @@ enum xiic_endian {
  * @endianness: big/little-endian byte order
  * @clk: Pointer to AXI4-lite input clock
  * @state: See STATE_
+ * @singlemaster: Indicates bus is single master
  */
 struct xiic_i2c {
 	struct device *dev;
@@ -74,6 +75,7 @@ struct xiic_i2c {
 	enum xiic_endian endianness;
 	struct clk *clk;
 	enum xilinx_i2c_state state;
+	bool singlemaster;
 };
 
 
@@ -526,6 +528,15 @@ static int xiic_busy(struct xiic_i2c *i2c)
 	if (i2c->tx_msg)
 		return -EBUSY;
 
+	/* In single master mode bus can only be busy, when in use by this
+	 * driver. If the register indicates bus being busy for some reason we
+	 * should ignore it, since bus will never be released and i2c will be
+	 * stuck forever.
+	 */
+	if (i2c->singlemaster) {
+		return 0;
+	}
+
 	/* for instance if previous transfer was terminated due to TX error
 	 * it might be that the bus is on it's way to become available
 	 * give it at most 3 ms to wake
@@ -811,6 +822,9 @@ static int xiic_i2c_probe(struct platform_device *pdev)
 		goto err_clk_dis;
 	}
 
+	i2c->singlemaster =
+		of_property_read_bool(pdev->dev.of_node, "single-master");
+
 	/*
 	 * Detect endianness
 	 * Try to reset the TX FIFO. Then check the EMPTY flag. If it is not
-- 
2.19.1


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Re: [PATCH 2/3] i2c: xiic: Improve struct memory alignment

[Michal Simek]

On 27. 08. 20 16:48, ext-jaakko.laine@vaisala.com wrote:
> From: Jaakko Laine <ext-jaakko.laine@vaisala.com>
> 
> xiic_i2c struct alignment causes the struct to
> take more space in memory than strictly required.
> Move state -member to end of struct to get less
> padding.
> 
> Signed-off-by: Jaakko Laine <ext-jaakko.laine@vaisala.com>
> Suggested-by: Michal Simek <michal.simek@xilinx.com>
> ---
>  drivers/i2c/busses/i2c-xiic.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-xiic.c b/drivers/i2c/busses/i2c-xiic.c
> index 10380531d45c..1453d82bb664 100644
> --- a/drivers/i2c/busses/i2c-xiic.c
> +++ b/drivers/i2c/busses/i2c-xiic.c
> @@ -54,11 +54,11 @@ enum xiic_endian {
>   * @lock: Mutual exclusion
>   * @tx_pos: Current pos in TX message
>   * @nmsgs: Number of messages in tx_msg
> - * @state: See STATE_
>   * @rx_msg: Current RX message
>   * @rx_pos: Position within current RX message
>   * @endianness: big/little-endian byte order
>   * @clk: Pointer to AXI4-lite input clock
> + * @state: See STATE_
>   */
>  struct xiic_i2c {
>  	struct device *dev;
> @@ -69,11 +69,11 @@ struct xiic_i2c {
>  	struct mutex lock;
>  	unsigned int tx_pos;
>  	unsigned int nmsgs;
> -	enum xilinx_i2c_state state;
>  	struct i2c_msg *rx_msg;
>  	int rx_pos;
>  	enum xiic_endian endianness;
>  	struct clk *clk;
> +	enum xilinx_i2c_state state;
>  };
>  
>  
> 

Acked-by: Michal Simek <michal.simek@xilinx.com>

Thanks,
Michal

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Re: [PATCH 3/3] i2c: xiic: Support forcing single-master in DT

[Michal Simek]

On 27. 08. 20 16:48, ext-jaakko.laine@vaisala.com wrote:
> From: Jaakko Laine <ext-jaakko.laine@vaisala.com>
> 
> I2C master operating in multimaster mode can get stuck
> indefinitely if I2C start is detected on bus, but no master
> has a transaction going.
> 
> This is a weakness in I2C standard, which defines no way
> to recover, since all masters are indefinitely disallowed
> from interrupting the currently operating master. A start
> condition can be created for example by an electromagnetic
> discharge applied near physical I2C lines. Or a already
> operating master could get reset immediately after sending
> a start.
> 
> If it is known during device tree creation that only a single
> I2C master will be present on the bus, this deadlock of the
> I2C bus could be avoided in the driver by ignoring the
> bus_is_busy register of the xiic, since bus can never be
> reserved by any other master.
> 
> This patch adds this support for detecting single-master flag
> in device tree and when provided, improves I2C reliability by
> ignoring the therefore unnecessary xiic bus_is_busy register.
> 
> Error can be reproduced by pulling I2C SDA -line temporarily low
> by shorting it to ground, while linux I2C master is operating on
> it using the xiic driver. The application using the bus will
> start receiving linux error code 16: "Device or resource busy"
> indefinitely:
> 
> kernel: pca953x 0-0020: failed writing register
> app: Error writing file, error: 16
> 
> With multi-master disabled device will instead receive error
> code 5: "I/O error" while SDA is grounded, but recover normal
> operation once short is removed.
> 
> kernel: pca953x 0-0020: failed reading register
> app: Error reading file, error: 5
> 
> Signed-off-by: Jaakko Laine <ext-jaakko.laine@vaisala.com>
> ---
>  drivers/i2c/busses/i2c-xiic.c | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
> 
> diff --git a/drivers/i2c/busses/i2c-xiic.c b/drivers/i2c/busses/i2c-xiic.c
> index 1453d82bb664..087b2951942e 100644
> --- a/drivers/i2c/busses/i2c-xiic.c
> +++ b/drivers/i2c/busses/i2c-xiic.c
> @@ -59,6 +59,7 @@ enum xiic_endian {
>   * @endianness: big/little-endian byte order
>   * @clk: Pointer to AXI4-lite input clock
>   * @state: See STATE_
> + * @singlemaster: Indicates bus is single master
>   */
>  struct xiic_i2c {
>  	struct device *dev;
> @@ -74,6 +75,7 @@ struct xiic_i2c {
>  	enum xiic_endian endianness;
>  	struct clk *clk;
>  	enum xilinx_i2c_state state;
> +	bool singlemaster;
>  };
>  
>  
> @@ -526,6 +528,15 @@ static int xiic_busy(struct xiic_i2c *i2c)
>  	if (i2c->tx_msg)
>  		return -EBUSY;
>  
> +	/* In single master mode bus can only be busy, when in use by this
> +	 * driver. If the register indicates bus being busy for some reason we
> +	 * should ignore it, since bus will never be released and i2c will be
> +	 * stuck forever.
> +	 */
> +	if (i2c->singlemaster) {
> +		return 0;
> +	}
> +
>  	/* for instance if previous transfer was terminated due to TX error
>  	 * it might be that the bus is on it's way to become available
>  	 * give it at most 3 ms to wake
> @@ -811,6 +822,9 @@ static int xiic_i2c_probe(struct platform_device *pdev)
>  		goto err_clk_dis;
>  	}
>  
> +	i2c->singlemaster =
> +		of_property_read_bool(pdev->dev.of_node, "single-master");
> +
>  	/*
>  	 * Detect endianness
>  	 * Try to reset the TX FIFO. Then check the EMPTY flag. If it is not
> 

Acked-by: Michal Simek <michal.simek@xilinx.com>

Thanks,
Michal

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Re: [PATCH 1/3] i2c: xiic: Change code alignment to 1 space only

[Wolfram Sang]

[-- Attachment #1.1: Type: text/plain, Size: 446 bytes --]

On Thu, Aug 27, 2020 at 05:48:46PM +0300, ext-jaakko.laine@vaisala.com wrote:
> From: Jaakko Laine <ext-jaakko.laine@vaisala.com>
> 
> Alignment removed and replaced with 1 space only to
> reduce need for future alignment changes affecting multiple
> lines, when new variables are added.
> 
> Signed-off-by: Jaakko Laine <ext-jaakko.laine@vaisala.com>
> Acked-by: Michal Simek <michal.simek@xilinx.com>

Applied to for-next, thanks!


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Re: [PATCH 2/3] i2c: xiic: Improve struct memory alignment

[Wolfram Sang]

[-- Attachment #1.1: Type: text/plain, Size: 458 bytes --]

On Thu, Aug 27, 2020 at 05:48:47PM +0300, ext-jaakko.laine@vaisala.com wrote:
> From: Jaakko Laine <ext-jaakko.laine@vaisala.com>
> 
> xiic_i2c struct alignment causes the struct to
> take more space in memory than strictly required.
> Move state -member to end of struct to get less
> padding.
> 
> Signed-off-by: Jaakko Laine <ext-jaakko.laine@vaisala.com>
> Suggested-by: Michal Simek <michal.simek@xilinx.com>

Applied to for-next, thanks!


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Re: [PATCH 3/3] i2c: xiic: Support forcing single-master in DT

[Wolfram Sang]

[-- Attachment #1.1: Type: text/plain, Size: 1889 bytes --]

On Thu, Aug 27, 2020 at 05:48:48PM +0300, ext-jaakko.laine@vaisala.com wrote:
> From: Jaakko Laine <ext-jaakko.laine@vaisala.com>
> 
> I2C master operating in multimaster mode can get stuck
> indefinitely if I2C start is detected on bus, but no master
> has a transaction going.
> 
> This is a weakness in I2C standard, which defines no way
> to recover, since all masters are indefinitely disallowed
> from interrupting the currently operating master. A start
> condition can be created for example by an electromagnetic
> discharge applied near physical I2C lines. Or a already
> operating master could get reset immediately after sending
> a start.
> 
> If it is known during device tree creation that only a single
> I2C master will be present on the bus, this deadlock of the
> I2C bus could be avoided in the driver by ignoring the
> bus_is_busy register of the xiic, since bus can never be
> reserved by any other master.
> 
> This patch adds this support for detecting single-master flag
> in device tree and when provided, improves I2C reliability by
> ignoring the therefore unnecessary xiic bus_is_busy register.
> 
> Error can be reproduced by pulling I2C SDA -line temporarily low
> by shorting it to ground, while linux I2C master is operating on
> it using the xiic driver. The application using the bus will
> start receiving linux error code 16: "Device or resource busy"
> indefinitely:
> 
> kernel: pca953x 0-0020: failed writing register
> app: Error writing file, error: 16
> 
> With multi-master disabled device will instead receive error
> code 5: "I/O error" while SDA is grounded, but recover normal
> operation once short is removed.
> 
> kernel: pca953x 0-0020: failed reading register
> app: Error reading file, error: 5
> 
> Signed-off-by: Jaakko Laine <ext-jaakko.laine@vaisala.com>

Applied to for-next, thanks!


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