[PATCH 1/2] of: base: Introduce of_alias_check_id() to check alias IDs

[PATCH 1/2] of: base: Introduce of_alias_check_id() to check alias IDs

[Michal Simek]

The function travers the lookup table to check if the request alias
id is compatible with the device driver match structure.
This function will be used by serial drivers to check if requested alias
is allocated or free to use.

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

Based on discussion with Rob
https://lkml.org/lkml/2018/4/27/397
nbits is passed to the function not to limit only to 32/64bit fields.

---
 drivers/of/base.c  | 48 ++++++++++++++++++++++++++++++++++++++++++++++++
 include/linux/of.h |  3 +++
 2 files changed, 51 insertions(+)

diff --git a/drivers/of/base.c b/drivers/of/base.c
index 466e3c8582f0..236a85d69957 100644
--- a/drivers/of/base.c
+++ b/drivers/of/base.c
@@ -16,6 +16,7 @@
 
 #define pr_fmt(fmt)	"OF: " fmt
 
+#include <linux/bitmap.h>
 #include <linux/console.h>
 #include <linux/ctype.h>
 #include <linux/cpu.h>
@@ -1893,6 +1894,53 @@ int of_alias_get_id(struct device_node *np, const char *stem)
 EXPORT_SYMBOL_GPL(of_alias_get_id);
 
 /**
+ * of_alias_get_alias_list - Get alias list for the given device driver
+ * @matches:	Array of OF device match structures to search in
+ * @stem:	Alias stem of the given device_node
+ * @bitmap:	Bitmap field pointer
+ * @nbits:	Maximum number of alias ID which can be recorded it bitmap
+ *
+ * The function travels the lookup table to record alias ids for the given
+ * device match structures and alias stem.
+ */
+void of_alias_get_alias_list(const struct of_device_id *matches,
+			     const char *stem, unsigned long *bitmap,
+			     unsigned int nbits)
+{
+	struct alias_prop *app;
+
+	/* Zero bitmap field to make sure that all the time it is clean */
+	bitmap_zero(bitmap, nbits);
+
+	mutex_lock(&of_mutex);
+	pr_debug("%s: Looking for stem: %s\n", __func__, stem);
+	list_for_each_entry(app, &aliases_lookup, link) {
+		pr_debug("%s: stem: %s, id: %d\n",
+			 __func__, app->stem, app->id);
+
+		if (strcmp(app->stem, stem) != 0) {
+			pr_debug("%s: stem comparison doesn't passed %s\n",
+				 __func__, app->stem);
+			continue;
+		}
+
+		if (app->id >= nbits) {
+			pr_debug("%s: ID %d greater then bitmap field %d\n",
+				__func__, app->id, nbits);
+			continue;
+		}
+
+		if (of_match_node(matches, app->np)) {
+			pr_debug("%s: Allocated ID %d\n", __func__, app->id);
+			set_bit(app->id, bitmap);
+		}
+		/* Alias exist but it not compatible with matches */
+	}
+	mutex_unlock(&of_mutex);
+}
+EXPORT_SYMBOL_GPL(of_alias_get_alias_list);
+
+/**
  * of_alias_get_highest_id - Get highest alias id for the given stem
  * @stem:	Alias stem to be examined
  *
diff --git a/include/linux/of.h b/include/linux/of.h
index 4d25e4f952d9..e474710e3930 100644
--- a/include/linux/of.h
+++ b/include/linux/of.h
@@ -387,6 +387,9 @@ extern int of_phandle_iterator_args(struct of_phandle_iterator *it,
 extern void of_alias_scan(void * (*dt_alloc)(u64 size, u64 align));
 extern int of_alias_get_id(struct device_node *np, const char *stem);
 extern int of_alias_get_highest_id(const char *stem);
+extern void of_alias_get_alias_list(const struct of_device_id *matches,
+				    const char *stem, unsigned long *bitmap,
+				    unsigned int nbits);
 
 extern int of_machine_is_compatible(const char *compat);
 
-- 
1.9.1

[PATCH 2/2] serial: uartps: Change uart ID port allocation

[Michal Simek]

For IPs which have alias algorightm all the time using that alias and
minor number. It means serial20 alias ends up as ttyPS20.

If alias is not setup for probed IP instance the first unused position is
used but that needs to be checked if it is really empty because another
instance doesn't need to be probed at that time. of_alias_get_alias_list()
fills alias bitmap which exactly shows which ID is free.
If alias pointing to different not compatible IP, it is free to use.

cdns_get_id() call is placed below structure allocation to simplify
error path.

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

Needs to be applied on the top of
https://lkml.org/lkml/2018/9/3/404
https://lkml.org/lkml/2018/9/3/400 (minor that's why just in case)

---
 drivers/tty/serial/xilinx_uartps.c | 106 ++++++++++++++++++++++++++++++++-----
 1 file changed, 93 insertions(+), 13 deletions(-)

diff --git a/drivers/tty/serial/xilinx_uartps.c b/drivers/tty/serial/xilinx_uartps.c
index 71c032744dae..61c4a644e143 100644
--- a/drivers/tty/serial/xilinx_uartps.c
+++ b/drivers/tty/serial/xilinx_uartps.c
@@ -30,7 +30,6 @@
 #define CDNS_UART_TTY_NAME	"ttyPS"
 #define CDNS_UART_NAME		"xuartps"
 #define CDNS_UART_MAJOR		0	/* use dynamic node allocation */
-#define CDNS_UART_NR_PORTS	2
 #define CDNS_UART_FIFO_SIZE	64	/* FIFO size */
 #define CDNS_UART_REGISTER_SPACE	0x1000
 
@@ -1370,6 +1369,85 @@ static int __maybe_unused cdns_runtime_resume(struct device *dev)
 };
 MODULE_DEVICE_TABLE(of, cdns_uart_of_match);
 
+/*
+ * Maximum number of instances without alias IDs but if there is alias
+ * which target "< MAX_UART_INSTANCES" range this ID can't be used.
+ */
+#define MAX_UART_INSTANCES	32
+
+/* Stores static aliases list */
+static DECLARE_BITMAP(alias_bitmap, MAX_UART_INSTANCES);
+static int alias_bitmap_initialized;
+
+/* Stores actual bitmap of allocated IDs with alias IDs together */
+static DECLARE_BITMAP(bitmap, MAX_UART_INSTANCES);
+/* Protect bitmap operations to have unique IDs */
+static DEFINE_MUTEX(bitmap_lock);
+
+static int cdns_get_id(struct platform_device *pdev)
+{
+	int id;
+
+	mutex_lock(&bitmap_lock);
+
+	/* Alias list is stable that's why get alias bitmap only once */
+	if (!alias_bitmap_initialized) {
+		of_alias_get_alias_list(cdns_uart_of_match, "serial",
+					alias_bitmap, MAX_UART_INSTANCES);
+		alias_bitmap_initialized++;
+	}
+
+	/* Make sure that alias ID is not taken by instance without alias */
+	bitmap_or(bitmap, bitmap, alias_bitmap, MAX_UART_INSTANCES);
+
+	dev_dbg(&pdev->dev, "Alias bitmap: %*pb\n",
+		MAX_UART_INSTANCES, bitmap);
+
+	/* Look for a serialN alias */
+	id = of_alias_get_id(pdev->dev.of_node, "serial");
+	if (id < 0) {
+		dev_warn(&pdev->dev,
+			 "No serial alias passed. Using the first free id\n");
+
+		/*
+		 * Start with id 0 and check if there is no serial0 alias
+		 * which points to device which is compatible with this driver.
+		 * If alias exists then try next free position.
+		 */
+		id = 0;
+
+		for (;;) {
+			dev_info(&pdev->dev, "Checking id %d\n", id);
+			id = find_next_zero_bit(bitmap, MAX_UART_INSTANCES, id);
+
+			/* No free empty instance */
+			if (id == MAX_UART_INSTANCES) {
+				dev_err(&pdev->dev, "No free ID\n");
+				mutex_unlock(&bitmap_lock);
+				return -EINVAL;
+			}
+
+			dev_dbg(&pdev->dev, "The empty id is %d\n", id);
+			/* Check if ID is empty */
+			if (!test_and_set_bit(id, bitmap)) {
+				/* Break the loop if bit is taken */
+				dev_dbg(&pdev->dev,
+					"Selected ID %d allocation passed\n",
+					id);
+				break;
+			}
+			dev_dbg(&pdev->dev,
+				"Selected ID %d allocation failed\n", id);
+			/* if taking bit fails then try next one */
+			id++;
+		}
+	}
+
+	mutex_unlock(&bitmap_lock);
+
+	return id;
+}
+
 /**
  * cdns_uart_probe - Platform driver probe
  * @pdev: Pointer to the platform device structure
@@ -1403,21 +1481,17 @@ static int cdns_uart_probe(struct platform_device *pdev)
 	if (!cdns_uart_uart_driver)
 		return -ENOMEM;
 
-	/* Look for a serialN alias */
-	cdns_uart_data->id = of_alias_get_id(pdev->dev.of_node, "serial");
+	cdns_uart_data->id = cdns_get_id(pdev);
 	if (cdns_uart_data->id < 0)
-		cdns_uart_data->id = 0;
-
-	if (cdns_uart_data->id >= CDNS_UART_NR_PORTS) {
-		dev_err(&pdev->dev, "Cannot get uart_port structure\n");
-		return -ENODEV;
-	}
+		return cdns_uart_data->id;
 
 	/* There is a need to use unique driver name */
 	driver_name = devm_kasprintf(&pdev->dev, GFP_KERNEL, "%s%d",
 				     CDNS_UART_NAME, cdns_uart_data->id);
-	if (!driver_name)
-		return -ENOMEM;
+	if (!driver_name) {
+		rc = -ENOMEM;
+		goto err_out_id;
+	}
 
 	cdns_uart_uart_driver->owner = THIS_MODULE;
 	cdns_uart_uart_driver->driver_name = driver_name;
@@ -1446,7 +1520,7 @@ static int cdns_uart_probe(struct platform_device *pdev)
 	rc = uart_register_driver(cdns_uart_uart_driver);
 	if (rc < 0) {
 		dev_err(&pdev->dev, "Failed to register driver\n");
-		return rc;
+		goto err_out_id;
 	}
 
 	cdns_uart_data->cdns_uart_driver = cdns_uart_uart_driver;
@@ -1587,7 +1661,10 @@ static int cdns_uart_probe(struct platform_device *pdev)
 	clk_disable_unprepare(cdns_uart_data->pclk);
 err_out_unregister_driver:
 	uart_unregister_driver(cdns_uart_data->cdns_uart_driver);
-
+err_out_id:
+	mutex_lock(&bitmap_lock);
+	clear_bit(cdns_uart_data->id, bitmap);
+	mutex_unlock(&bitmap_lock);
 	return rc;
 }
 
@@ -1610,6 +1687,9 @@ static int cdns_uart_remove(struct platform_device *pdev)
 #endif
 	rc = uart_remove_one_port(cdns_uart_data->cdns_uart_driver, port);
 	port->mapbase = 0;
+	mutex_lock(&bitmap_lock);
+	clear_bit(cdns_uart_data->id, bitmap);
+	mutex_unlock(&bitmap_lock);
 	clk_disable_unprepare(cdns_uart_data->uartclk);
 	clk_disable_unprepare(cdns_uart_data->pclk);
 	pm_runtime_disable(&pdev->dev);
-- 
1.9.1

Re: [PATCH 1/2] of: base: Introduce of_alias_check_id() to check alias IDs

[Michal Simek]

[-- Attachment #1.1: Type: text/plain, Size: 3895 bytes --]

Hi Rob,

On 3.9.2018 15:14, Michal Simek wrote:
> The function travers the lookup table to check if the request alias
> id is compatible with the device driver match structure.
> This function will be used by serial drivers to check if requested alias
> is allocated or free to use.
> 
> Signed-off-by: Michal Simek <michal.simek@xilinx.com>
> ---
> 
> Based on discussion with Rob
> https://lkml.org/lkml/2018/4/27/397
> nbits is passed to the function not to limit only to 32/64bit fields.
> 
> ---
>  drivers/of/base.c  | 48 ++++++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/of.h |  3 +++
>  2 files changed, 51 insertions(+)
> 
> diff --git a/drivers/of/base.c b/drivers/of/base.c
> index 466e3c8582f0..236a85d69957 100644
> --- a/drivers/of/base.c
> +++ b/drivers/of/base.c
> @@ -16,6 +16,7 @@
>  
>  #define pr_fmt(fmt)	"OF: " fmt
>  
> +#include <linux/bitmap.h>
>  #include <linux/console.h>
>  #include <linux/ctype.h>
>  #include <linux/cpu.h>
> @@ -1893,6 +1894,53 @@ int of_alias_get_id(struct device_node *np, const char *stem)
>  EXPORT_SYMBOL_GPL(of_alias_get_id);
>  
>  /**
> + * of_alias_get_alias_list - Get alias list for the given device driver
> + * @matches:	Array of OF device match structures to search in
> + * @stem:	Alias stem of the given device_node
> + * @bitmap:	Bitmap field pointer
> + * @nbits:	Maximum number of alias ID which can be recorded it bitmap
> + *
> + * The function travels the lookup table to record alias ids for the given
> + * device match structures and alias stem.
> + */
> +void of_alias_get_alias_list(const struct of_device_id *matches,
> +			     const char *stem, unsigned long *bitmap,
> +			     unsigned int nbits)
> +{
> +	struct alias_prop *app;
> +
> +	/* Zero bitmap field to make sure that all the time it is clean */
> +	bitmap_zero(bitmap, nbits);
> +
> +	mutex_lock(&of_mutex);
> +	pr_debug("%s: Looking for stem: %s\n", __func__, stem);
> +	list_for_each_entry(app, &aliases_lookup, link) {
> +		pr_debug("%s: stem: %s, id: %d\n",
> +			 __func__, app->stem, app->id);
> +
> +		if (strcmp(app->stem, stem) != 0) {
> +			pr_debug("%s: stem comparison doesn't passed %s\n",
> +				 __func__, app->stem);
> +			continue;
> +		}
> +
> +		if (app->id >= nbits) {
> +			pr_debug("%s: ID %d greater then bitmap field %d\n",
> +				__func__, app->id, nbits);
> +			continue;
> +		}
> +
> +		if (of_match_node(matches, app->np)) {
> +			pr_debug("%s: Allocated ID %d\n", __func__, app->id);
> +			set_bit(app->id, bitmap);
> +		}
> +		/* Alias exist but it not compatible with matches */
> +	}
> +	mutex_unlock(&of_mutex);
> +}
> +EXPORT_SYMBOL_GPL(of_alias_get_alias_list);
> +
> +/**
>   * of_alias_get_highest_id - Get highest alias id for the given stem
>   * @stem:	Alias stem to be examined
>   *
> diff --git a/include/linux/of.h b/include/linux/of.h
> index 4d25e4f952d9..e474710e3930 100644
> --- a/include/linux/of.h
> +++ b/include/linux/of.h
> @@ -387,6 +387,9 @@ extern int of_phandle_iterator_args(struct of_phandle_iterator *it,
>  extern void of_alias_scan(void * (*dt_alloc)(u64 size, u64 align));
>  extern int of_alias_get_id(struct device_node *np, const char *stem);
>  extern int of_alias_get_highest_id(const char *stem);
> +extern void of_alias_get_alias_list(const struct of_device_id *matches,
> +				    const char *stem, unsigned long *bitmap,
> +				    unsigned int nbits);
>  
>  extern int of_machine_is_compatible(const char *compat);
>  
> 

Can you please take a look at this patch?

Thanks,
Michal

-- 
Michal Simek, Ing. (M.Eng), OpenPGP -> KeyID: FE3D1F91
w: www.monstr.eu p: +42-0-721842854
Maintainer of Linux kernel - Xilinx Microblaze
Maintainer of Linux kernel - Xilinx Zynq ARM and ZynqMP ARM64 SoCs
U-Boot custodian - Xilinx Microblaze/Zynq/ZynqMP SoCs




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Re: [PATCH 1/2] of: base: Introduce of_alias_check_id() to check alias IDs

[Rob Herring]

On Mon, Sep 3, 2018 at 8:14 AM Michal Simek <michal.simek@xilinx.com> wrote:
>
> The function travers the lookup table to check if the request alias
> id is compatible with the device driver match structure.
> This function will be used by serial drivers to check if requested alias
> is allocated or free to use.
>
> Signed-off-by: Michal Simek <michal.simek@xilinx.com>
> ---
>
> Based on discussion with Rob
> https://lkml.org/lkml/2018/4/27/397
> nbits is passed to the function not to limit only to 32/64bit fields.
>
> ---
>  drivers/of/base.c  | 48 ++++++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/of.h |  3 +++
>  2 files changed, 51 insertions(+)
>
> diff --git a/drivers/of/base.c b/drivers/of/base.c
> index 466e3c8582f0..236a85d69957 100644
> --- a/drivers/of/base.c
> +++ b/drivers/of/base.c
> @@ -16,6 +16,7 @@
>
>  #define pr_fmt(fmt)    "OF: " fmt
>
> +#include <linux/bitmap.h>
>  #include <linux/console.h>
>  #include <linux/ctype.h>
>  #include <linux/cpu.h>
> @@ -1893,6 +1894,53 @@ int of_alias_get_id(struct device_node *np, const char *stem)
>  EXPORT_SYMBOL_GPL(of_alias_get_id);
>
>  /**
> + * of_alias_get_alias_list - Get alias list for the given device driver
> + * @matches:   Array of OF device match structures to search in
> + * @stem:      Alias stem of the given device_node
> + * @bitmap:    Bitmap field pointer
> + * @nbits:     Maximum number of alias ID which can be recorded it bitmap
> + *
> + * The function travels the lookup table to record alias ids for the given
> + * device match structures and alias stem.
> + */
> +void of_alias_get_alias_list(const struct of_device_id *matches,
> +                            const char *stem, unsigned long *bitmap,
> +                            unsigned int nbits)
> +{
> +       struct alias_prop *app;
> +
> +       /* Zero bitmap field to make sure that all the time it is clean */
> +       bitmap_zero(bitmap, nbits);
> +
> +       mutex_lock(&of_mutex);
> +       pr_debug("%s: Looking for stem: %s\n", __func__, stem);
> +       list_for_each_entry(app, &aliases_lookup, link) {
> +               pr_debug("%s: stem: %s, id: %d\n",
> +                        __func__, app->stem, app->id);
> +
> +               if (strcmp(app->stem, stem) != 0) {
> +                       pr_debug("%s: stem comparison doesn't passed %s\n",
> +                                __func__, app->stem);
> +                       continue;
> +               }
> +
> +               if (app->id >= nbits) {
> +                       pr_debug("%s: ID %d greater then bitmap field %d\n",
> +                               __func__, app->id, nbits);
> +                       continue;
> +               }
> +
> +               if (of_match_node(matches, app->np)) {
> +                       pr_debug("%s: Allocated ID %d\n", __func__, app->id);
> +                       set_bit(app->id, bitmap);
> +               }
> +               /* Alias exist but it not compatible with matches */
> +       }
> +       mutex_unlock(&of_mutex);
> +}
> +EXPORT_SYMBOL_GPL(of_alias_get_alias_list);
> +
> +/**
>   * of_alias_get_highest_id - Get highest alias id for the given stem
>   * @stem:      Alias stem to be examined
>   *
> diff --git a/include/linux/of.h b/include/linux/of.h
> index 4d25e4f952d9..e474710e3930 100644
> --- a/include/linux/of.h
> +++ b/include/linux/of.h
> @@ -387,6 +387,9 @@ extern int of_phandle_iterator_args(struct of_phandle_iterator *it,
>  extern void of_alias_scan(void * (*dt_alloc)(u64 size, u64 align));
>  extern int of_alias_get_id(struct device_node *np, const char *stem);
>  extern int of_alias_get_highest_id(const char *stem);
> +extern void of_alias_get_alias_list(const struct of_device_id *matches,
> +                                   const char *stem, unsigned long *bitmap,
> +                                   unsigned int nbits);

You should go ahead and add an empty function too as the other 2 alias
functions have one.

With that, I'm assuming this is going with your serial patches:

Reviewed-by: Rob Herring <robh@kernel.org>

Re: [PATCH 1/2] of: base: Introduce of_alias_check_id() to check alias IDs

[Michal Simek]

On 13.9.2018 20:53, Rob Herring wrote:
> On Mon, Sep 3, 2018 at 8:14 AM Michal Simek <michal.simek@xilinx.com> wrote:
>>
>> The function travers the lookup table to check if the request alias
>> id is compatible with the device driver match structure.
>> This function will be used by serial drivers to check if requested alias
>> is allocated or free to use.
>>
>> Signed-off-by: Michal Simek <michal.simek@xilinx.com>
>> ---
>>
>> Based on discussion with Rob
>> https://lkml.org/lkml/2018/4/27/397
>> nbits is passed to the function not to limit only to 32/64bit fields.
>>
>> ---
>>  drivers/of/base.c  | 48 ++++++++++++++++++++++++++++++++++++++++++++++++
>>  include/linux/of.h |  3 +++
>>  2 files changed, 51 insertions(+)
>>
>> diff --git a/drivers/of/base.c b/drivers/of/base.c
>> index 466e3c8582f0..236a85d69957 100644
>> --- a/drivers/of/base.c
>> +++ b/drivers/of/base.c
>> @@ -16,6 +16,7 @@
>>
>>  #define pr_fmt(fmt)    "OF: " fmt
>>
>> +#include <linux/bitmap.h>
>>  #include <linux/console.h>
>>  #include <linux/ctype.h>
>>  #include <linux/cpu.h>
>> @@ -1893,6 +1894,53 @@ int of_alias_get_id(struct device_node *np, const char *stem)
>>  EXPORT_SYMBOL_GPL(of_alias_get_id);
>>
>>  /**
>> + * of_alias_get_alias_list - Get alias list for the given device driver
>> + * @matches:   Array of OF device match structures to search in
>> + * @stem:      Alias stem of the given device_node
>> + * @bitmap:    Bitmap field pointer
>> + * @nbits:     Maximum number of alias ID which can be recorded it bitmap
>> + *
>> + * The function travels the lookup table to record alias ids for the given
>> + * device match structures and alias stem.
>> + */
>> +void of_alias_get_alias_list(const struct of_device_id *matches,
>> +                            const char *stem, unsigned long *bitmap,
>> +                            unsigned int nbits)
>> +{
>> +       struct alias_prop *app;
>> +
>> +       /* Zero bitmap field to make sure that all the time it is clean */
>> +       bitmap_zero(bitmap, nbits);
>> +
>> +       mutex_lock(&of_mutex);
>> +       pr_debug("%s: Looking for stem: %s\n", __func__, stem);
>> +       list_for_each_entry(app, &aliases_lookup, link) {
>> +               pr_debug("%s: stem: %s, id: %d\n",
>> +                        __func__, app->stem, app->id);
>> +
>> +               if (strcmp(app->stem, stem) != 0) {
>> +                       pr_debug("%s: stem comparison doesn't passed %s\n",
>> +                                __func__, app->stem);
>> +                       continue;
>> +               }
>> +
>> +               if (app->id >= nbits) {
>> +                       pr_debug("%s: ID %d greater then bitmap field %d\n",
>> +                               __func__, app->id, nbits);
>> +                       continue;
>> +               }
>> +
>> +               if (of_match_node(matches, app->np)) {
>> +                       pr_debug("%s: Allocated ID %d\n", __func__, app->id);
>> +                       set_bit(app->id, bitmap);
>> +               }
>> +               /* Alias exist but it not compatible with matches */
>> +       }
>> +       mutex_unlock(&of_mutex);
>> +}
>> +EXPORT_SYMBOL_GPL(of_alias_get_alias_list);
>> +
>> +/**
>>   * of_alias_get_highest_id - Get highest alias id for the given stem
>>   * @stem:      Alias stem to be examined
>>   *
>> diff --git a/include/linux/of.h b/include/linux/of.h
>> index 4d25e4f952d9..e474710e3930 100644
>> --- a/include/linux/of.h
>> +++ b/include/linux/of.h
>> @@ -387,6 +387,9 @@ extern int of_phandle_iterator_args(struct of_phandle_iterator *it,
>>  extern void of_alias_scan(void * (*dt_alloc)(u64 size, u64 align));
>>  extern int of_alias_get_id(struct device_node *np, const char *stem);
>>  extern int of_alias_get_highest_id(const char *stem);
>> +extern void of_alias_get_alias_list(const struct of_device_id *matches,
>> +                                   const char *stem, unsigned long *bitmap,
>> +                                   unsigned int nbits);
> 
> You should go ahead and add an empty function too as the other 2 alias
> functions have one.

ok. I have added that function. Also I realized that this function
should return return value to let users know if this function is not
returning proper values. I have updated this in v2.

> 
> With that, I'm assuming this is going with your serial patches:

yes that will be the best because serial driver is only one user.

> 
> Reviewed-by: Rob Herring <robh@kernel.org>

Added to v2. If you don't agree with also adding return value please let
me know.

Thanks,
Michal