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

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Date:   Sat, 7 Aug 2021 13:42:12 +0800
From:   Kent Gibson <warthog618@...il.com>
To:     Dipen Patel <dipenp@...dia.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 Fri, Aug 06, 2021 at 10:35:10PM -0700, Dipen Patel wrote:
> 
> 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.

My point is that the peculiarities of the hardware should be hidden from
the hte API user, especially if it is only necessary for some hardware.

> > 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.

And your current way every other hte user will have to duplicate the
gpiolib-cdev code....

> 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.
> 

Indeed.

Cheers,
Kent.

> >
> > 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.