From: Rodolfo Giometti <giometti@enneenne.com>
To: Charlie Johnston <charlie.johnston@ni.com>
Cc: linux-kernel@vger.kernel.org, brenda.streiff@ni.com
Subject: Re: [RFC PATCH] pps: Increase PPS_MAX_SOURCES value.
Date: Mon, 12 Jun 2023 18:07:52 +0200 [thread overview]
Message-ID: <5aff32cf-74ea-b632-9d4d-a01ca0d31821@enneenne.com> (raw)
In-Reply-To: <38f38f66-0fd5-4e6c-4839-8272cef77046@ni.com>
On 09/06/23 23:00, Charlie Johnston wrote:
> On 6/9/23 02:30, Rodolfo Giometti wrote:
>> On 08/06/23 00:07, Charlie Johnston wrote:
>>> On 6/7/23 02:33, Rodolfo Giometti wrote:
>>>> 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@ni.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
>>>>
>>>
>>> Thanks for taking a look!
>>>
>>> My understanding is that idr_alloc(..., start, end, ...) can take any end value up to INT_MAX. It also handles any values <= 0 by treating them as equal to INT_MAX + 1 since the end value is non-inclusive. I can't think of any reason using MINORMASK + 1 here would be an issue since it's much less than the maximum value idr_alloc() allows.
>>>
>>> A number of drivers (e.g. ptp) just explicitly use a start and end value of 0, but I don't think that change would fit here.
>>
>> I see and maybe I should replace the usage of idr_*() with ida_*() as PTP does...
>>
>> However the right-thing(TM) to do here should be dropping PPS_MAX_SOURCES at all!
>>
>> Let me go deeper in this issue. I'm going to produce a patch set in next days. Have you any chances to test it?
>>
>> Ciao,
>>
>> Rodolfo
>>
> MINORMASK
> I'll have to check when the system we used for testing is available again (not easy to find a system with 20+ Ethernet ports) but I'd be happy to test a patch!
Great! Please, let me know.
> I know an increase to PPS_MAX_SOURCES was tested on that system.
I see and it seems that it's safer to set PPS_MAX_SOURCES to MINORMASK... so
please reproduce your patch with this simple modification, then I'm going to
produce a patch to drop the PPS_MAX_SOURCES define since it's not needed anymore.
After that you should test all these modifications in order to safely add them
to Linux.
Ciao,
Rodolfo
--
GNU/Linux Solutions e-mail: giometti@enneenne.com
Linux Device Driver giometti@linux.it
Embedded Systems phone: +39 349 2432127
UNIX programming skype: rodolfo.giometti
next prev parent reply other threads:[~2023-06-12 16:08 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-06-05 20:31 [RFC PATCH] pps: Increase PPS_MAX_SOURCES value Charlie Johnston
2023-06-07 7:33 ` Rodolfo Giometti
2023-06-07 22:07 ` Charlie Johnston
2023-06-09 7:30 ` Rodolfo Giometti
2023-06-09 21:00 ` Charlie Johnston
2023-06-12 16:07 ` Rodolfo Giometti [this message]
2023-06-20 20:42 ` Charlie Johnston
2023-06-21 15:31 ` Rodolfo Giometti
2023-06-23 2:03 ` Charlie Johnston
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