linux-kernel - Re: [RFC PATCH] pps: Increase PPS_MAX

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Message-ID: <fe435e68-8e05-9078-0fe6-63ef7cce2fc9@enneenne.com>
Date:   Wed, 7 Jun 2023 09:33:27 +0200
From:   Rodolfo Giometti <giometti@...eenne.com>
To:     Charlie Johnston <charlie.johnston@...com>
Cc:     linux-kernel@...r.kernel.org, brenda.streiff@...com
Subject: Re: [RFC PATCH] pps: Increase PPS_MAX_SOURCES value.

On 05/06/23 22:31, Charlie Johnston wrote:
> For consistency with what ptp uses for minors, this
> change sets PPS_MAX_SOURCES to MINORMASK + 1.
> 
> The PPS_MAX_SOURCES value is currently set to 16. In
> some cases this was not sufficient for a system. For
> example, a system with multiple (4+) PCIe cards each
> with 4 PTP-capable ethernet interfaces could run out
> of the available PPS major:minors if each interface
> registers a PPS source.
> 
> Signed-off-by: Charlie Johnston <charlie.johnston@...com>
> ---
>   include/uapi/linux/pps.h | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/uapi/linux/pps.h b/include/uapi/linux/pps.h
> index 009ebcd8ced5..85f472330da8 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		(MINORMASK + 1)
>   
>   /* Implementation note: the logical states ``assert'' and ``clear''
>    * are implemented in terms of the chip register, i.e. ``assert''

I have just one question: are you sure that it's safe to call idr_alloc(..., 0, 
(MINORMASK + 1), ...)?

Ciao,

Rodolfo

-- 
GNU/Linux Solutions                  e-mail: giometti@...eenne.com
Linux Device Driver                          giometti@...ux.it
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UNIX programming                     skype:  rodolfo.giometti