Re: [RFC PATCH v2 0/7] of: Introduce hardware prober driver

From: Rob Herring <robh+dt@kernel.org>
To: Doug Anderson <dianders@chromium.org>
Cc: AngeloGioacchino Del Regno 
	<angelogioacchino.delregno@collabora.com>,
	Chen-Yu Tsai <wenst@chromium.org>,
	Frank Rowand <frowand.list@gmail.com>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
	Conor Dooley <conor+dt@kernel.org>,
	Matthias Brugger <matthias.bgg@gmail.com>,
	Hsin-Yi Wang <hsinyi@chromium.org>,
	Dmitry Torokhov <dmitry.torokhov@gmail.com>,
	andriy.shevchenko@linux.intel.com, Jiri Kosina <jikos@kernel.org>,
	linus.walleij@linaro.org, broonie@kernel.org,
	gregkh@linuxfoundation.org, hdegoede@redhat.com,
	james.clark@arm.com, james@equiv.tech, keescook@chromium.org,
	petr.tesarik.ext@huawei.com, rafael@kernel.org,
	tglx@linutronix.de, Jeff LaBundy <jeff@labundy.com>,
	linux-input@vger.kernel.org, devicetree@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-mediatek@lists.infradead.org, linux-kernel@vger.kernel.org,
	Johan Hovold <johan@kernel.org>
Subject: Re: [RFC PATCH v2 0/7] of: Introduce hardware prober driver
Date: Wed, 15 Nov 2023 13:28:12 -0600	[thread overview]
Message-ID: <CAL_Jsq+puq20EWkQg1RTs2zfmh4DGbqz1krp+19c=wPXnLT5dA@mail.gmail.com> (raw)
In-Reply-To: <CAD=FV=VUZy9DaZgKafSpXXopD5k8ExGSR97BjAqC5tupPoxNfQ@mail.gmail.com>

On Fri, Nov 10, 2023 at 6:12 PM Doug Anderson <dianders@chromium.org> wrote:
>
> Hi,
>
> On Thu, Nov 9, 2023 at 5:52 AM Rob Herring <robh+dt@kernel.org> wrote:
> >
> > > > End of background from Doug's cover letter.
> > >
> > > I think that using "status" is not a good idea, I find that confusing.
> >
> > "status" is what defines a device's state in terms of enabled,
> > present, available. That's exactly what we're expressing here.
> >
> > Now, I do not think we should be mixing the device class (e.g.
> > touchscreen) into status. I said this on v1, but apparently that was
> > not listened to.
>
> Interesting. I must have missed the "don't mix device class into
> status" part. Do you have a link to your post about that? Maybe
> there's other stuff I missed... Having the device class stuck at the
> end there was at least part of my last post [1] which gathered no
> response.

https://lore.kernel.org/all/CAL_JsqKK0tjeXNv=a8L3k0AjhCa15XOq1tPWqVod9mycsKXJHg@mail.gmail.com/

"I would not combine the 2 things. Knowing the class/type of the device
may be useful independent of your problem."

> I think one of the reasons that I felt we needed to mux the device
> class into status was that it was going to make the code a lot less
> fragile. Everything I've seen indicates that you don't want us to
> create a "HW prober" node that could be used to provide relevant
> phandles for different classes of devices, so the "HW prober" code
> needs to either search through the whole device tree for a status of
> "failed-needs-probe" or needs to contain per-board, hardcoded,
> fully-qualified paths.
>
> I don't think we want to include hardcoded, fully-qualified paths in
> the code. That would mean that if someone changed a node name
> somewhere in the path to one of the devices that we're dealing with
> then it would break.

Right, nothing should depend on the full path. That's not an ABI just
like the device path in sysfs is not (despite what Android HALs do).

> So if we're searching the whole device tree for "failed-needs-probe"
> then we need to figure out which devices are related to each other. If
> a given board has second sources for MIPI panels, touchscreens, and
> trackpads then we need to know which of the "failed-needs-probe"
> devices are trackpads, which are touchscreens, and which are MIPI
> panels. Do you have any suggestions for how we should do that? Maybe
> it was in some other thread that I missed? I guess we could have a
> board-specific table mapping (compatible + node name + reg) to a
> class, but that feels awkward.

Node name is supposed to correspond to device class, so why not use
that (no path or unit-address.) and nothing else (well, besides
"status")?

Rob