Re: [RFC PATCH] pps: make number of PPS devices configurable

[Rodolfo Giometti <giometti@enneenne.com>]

On 5/14/26 13:26, Vadim Fedorenko wrote:
> Modern systems may have more than 16 PPS sources and current hard-coded
> limit breaks registration of some devices. Make the limit configurable
> via Kconfig, keep default value of 16 devices. UAPI has to be changed to
> support maximum possible number.
> 
> Signed-off-by: Vadim Fedorenko <vadim.fedorenko@linux.dev>
> ---
>   drivers/pps/Kconfig      | 9 +++++++++
>   drivers/pps/pps.c        | 6 +++---
>   include/uapi/linux/pps.h | 2 +-
>   3 files changed, 13 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/pps/Kconfig b/drivers/pps/Kconfig
> index e1651d51cfc9..166c157505fe 100644
> --- a/drivers/pps/Kconfig
> +++ b/drivers/pps/Kconfig
> @@ -22,6 +22,15 @@ menuconfig PPS
>   
>   if PPS
>   
> +config PPS_NR_SOURCES
> +	int "Maximum number of PPS devices"
> +	depends on PPS
> +	range 16 256
> +	default "16"
> +	help
> +	  Set this to the number of PPS devices you want the driver
> +	  to support.
> +
>   config PPS_DEBUG
>   	bool "PPS debugging messages"
>   	help
> diff --git a/drivers/pps/pps.c b/drivers/pps/pps.c
> index de1122bb69ea..d3eac77b4cb5 100644
> --- a/drivers/pps/pps.c
> +++ b/drivers/pps/pps.c
> @@ -370,7 +370,7 @@ int pps_register_cdev(struct pps_device *pps)
>   	 * Get new ID for the new PPS source.  After idr_alloc() calling
>   	 * the new source will be freely available into the kernel.
>   	 */
> -	err = idr_alloc(&pps_idr, pps, 0, PPS_MAX_SOURCES, GFP_KERNEL);
> +	err = idr_alloc(&pps_idr, pps, 0, CONFIG_PPS_NR_SOURCES, GFP_KERNEL);
>   	if (err < 0) {
>   		if (err == -ENOSPC) {
>   			pr_err("%s: too many PPS sources in the system\n",
> @@ -464,7 +464,7 @@ EXPORT_SYMBOL(pps_lookup_dev);
>   static void __exit pps_exit(void)
>   {
>   	class_unregister(&pps_class);
> -	__unregister_chrdev(pps_major, 0, PPS_MAX_SOURCES, "pps");
> +	__unregister_chrdev(pps_major, 0, CONFIG_PPS_NR_SOURCES, "pps");
>   }
>   
>   static int __init pps_init(void)
> @@ -477,7 +477,7 @@ static int __init pps_init(void)
>   		return err;
>   	}
>   
> -	pps_major = __register_chrdev(0, 0, PPS_MAX_SOURCES, "pps",
> +	pps_major = __register_chrdev(0, 0, CONFIG_PPS_NR_SOURCES, "pps",
>   				      &pps_cdev_fops);
>   	if (pps_major < 0) {
>   		pr_err("failed to allocate char device region\n");
> diff --git a/include/uapi/linux/pps.h b/include/uapi/linux/pps.h
> index 009ebcd8ced5..1088dea65e12 100644
> --- a/include/uapi/linux/pps.h
> +++ b/include/uapi/linux/pps.h
> @@ -26,7 +26,7 @@
>   #include <linux/types.h>
>   
>   #define PPS_VERSION		"5.3.6"
> -#define PPS_MAX_SOURCES		16		/* should be enough... */
> +#define PPS_MAX_SOURCES		256		/* should be enough... */

Nak. Let's make everything configurable, or let's leave it constant. 256 is OK.

Ciao,

Rodolfo

>   /* Implementation note: the logical states ``assert'' and ``clear''
>    * are implemented in terms of the chip register, i.e. ``assert''


-- 
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