linux-kernel - Re: [RFC 03/11] hte: Add tegra194 HTE kernel provider

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Message-ID: <7f6a2591-c264-e005-18ae-242320d4a22e@nvidia.com>
Date:   Fri, 6 Aug 2021 22:35:10 -0700
From:   Dipen Patel <dipenp@...dia.com>
To:     Kent Gibson <warthog618@...il.com>
CC:     <thierry.reding@...il.com>, <jonathanh@...dia.com>,
        <linux-kernel@...r.kernel.org>, <linux-tegra@...r.kernel.org>,
        <linux-gpio@...r.kernel.org>, <linus.walleij@...aro.org>,
        <bgolaszewski@...libre.com>, <devicetree@...r.kernel.org>,
        <linux-doc@...r.kernel.org>, <robh+dt@...nel.org>
Subject: Re: [RFC 03/11] hte: Add tegra194 HTE kernel provider


On 8/6/21 9:51 PM, Kent Gibson wrote:
> On Fri, Aug 06, 2021 at 09:52:54PM -0700, Dipen Patel wrote:
>> On 8/6/21 8:07 PM, Kent Gibson wrote:
>>> On Fri, Aug 06, 2021 at 07:41:09PM -0700, Dipen Patel wrote:
>>>> On 7/31/21 8:43 AM, Kent Gibson wrote:
>>>>> On Wed, Jul 28, 2021 at 04:59:08PM -0700, Dipen Patel wrote:
>>>>>> Thanks Kent for the review comment. My responses inline.
>>>>>>
> <snip>
>
>>>> 2. Does hte handler solution create race between two handlers? i.e. edge_irq_handler and
>>>>
>>>> hte_handler, for the worst case scenario as below?
>>>>
>>> No.  If hardware timestamp is selected then no irq is requested from the
>>> irq subsystem for that line - only from the hte subsystem instead.
>>> So there will be no edge_irq_handler call for that line, so no possible race.
>> That is not possible for certain providers, for example the one I am dealing
>>
>> with which requires GPIO line to be requested as input and IRQ needs to
>>
>> be enabled on them.
>>
> So, for your hte subsystem to work, the consumer has to also request
> a line from the irq subsystem?

Yes

>   That makes sense to you?
Its not me, its peculiarity of the hardware that I am dealing with.
> Have hte do that, rather than the consumer.

Sure, for cdev it would mean to duplicate (most of) the edge* or line_create

code in HTE. For such hardware, my initial doubt remains the same about

the worst case scenario between two handlers, but perhaps that's

implementation details for hte to handle.

>
> And another reason it makes sense to integrate this with irq...

Alright, will explore this route as well. I remember both Thierry[1] and

Marc[2] raised some doubts (time to revive that discussion).


[1]: https://lore.kernel.org/lkml/YFm9r%2FtFkzVlYDEp@orome.fritz.box/

[2]: https://lore.kernel.org/lkml/87h7l1k9yi.wl-maz@kernel.org/

>
> Cheers,
> Kent.