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Date: Mon, 12 Jun 2023 18:07:52 +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 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@...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@...eenne.com Linux Device Driver giometti@...ux.it Embedded Systems phone: +39 349 2432127 UNIX programming skype: rodolfo.giometti
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