Re: [PATCH] arm64: dts: qcom: sc7280: Add touchscreen to villager

From: Konrad Dybcio
Date: Tue May 24 2022 - 19:57:34 EST


On 25/05/2022 00:55, Doug Anderson wrote:
Hi,

On Tue, May 24, 2022 at 3:41 PM Konrad Dybcio
<konrad.dybcio@xxxxxxxxxxxxxx> wrote:

On 25/05/2022 00:14, Doug Anderson wrote:
Hi,

On Tue, May 24, 2022 at 2:13 PM Konrad Dybcio
<konrad.dybcio@xxxxxxxxxxxxxx> wrote:
On 24/05/2022 22:48, Douglas Anderson wrote:
This adds the touchscreen to the sc7280-herobrine-villager device
tree. Note that the touchscreen on villager actually uses the reset
line and thus we use the more specific "elan,ekth6915" compatible
which allows us to specify the reset.

The fact that villager's touchscreen uses the reset line can be
contrasted against the touchscreen for CRD/herobrine-r1. On those
boards, even though the touchscreen goes to the display, it's not
hooked up to anything there.

In order to keep the line parked on herobrine/CRD, we'll move the
pullup from the qcard.dtsi file to the specific boards. This allows us
to disable the pullup in the villager device tree since the pin is an
output.

Signed-off-by: Douglas Anderson <dianders@xxxxxxxxxxxx>
---
This uses bindings introduced in the patch ("dt-bindings: HID:
i2c-hid: elan: Introduce bindings for Elan eKTH6915") [1].

[1] https://lore.kernel.org/r/20220523142257.v2.1.Iedc61f9ef220a89af6a031200a7850a27a440134@changeid

.../boot/dts/qcom/sc7280-herobrine-crd.dts | 11 ++++++++
.../qcom/sc7280-herobrine-herobrine-r1.dts | 11 ++++++++
.../dts/qcom/sc7280-herobrine-villager-r0.dts | 25 +++++++++++++++++++
arch/arm64/boot/dts/qcom/sc7280-qcard.dtsi | 1 -
4 files changed, 47 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/boot/dts/qcom/sc7280-herobrine-crd.dts b/arch/arm64/boot/dts/qcom/sc7280-herobrine-crd.dts
index a4ac33c4fd59..b79d84d7870a 100644
--- a/arch/arm64/boot/dts/qcom/sc7280-herobrine-crd.dts
+++ b/arch/arm64/boot/dts/qcom/sc7280-herobrine-crd.dts
@@ -134,6 +134,17 @@ &sdhc_2 {
status = "okay";
};

+/* PINCTRL - ADDITIONS TO NODES IN PARENT DEVICE TREE FILES */
Please drop this line, this isn't msm-3.4. It's immediately obvious that
if a pin is referenced by a label and it is not defined in this file
(because otherwise it wouldn't be both defined and referenced here..),
it comes from a previously included device tree.
In general these headings specify a change in sort ordering. Without
them then either we intersperse pinctrl overrides with other stuff,
which IMO is overall worse or people have no idea why the sort
ordering changes.
I get what you mean, but at the end of the day, the entire machine DT
specifies all machine-specific changes and only machine-specific
changes. They all are a part of a bigger picture, sometimes being
downstream from the SoC, sometimes downstream from a common board. I
don't think it brings much benefit if at all to separate them into
sections like these, if in the end they all correspond to modifications
present in the hardware. In its current form, the sorting is all over
the place, and ideally we could have labels sorted alphabetically.
I think overall DT just made it hard. In my mind the root of the
problem is actually that we're trying to avoid replicating hierarchy
from the dtsi files that we include. In other words, we try very hard
to do:

&qup_i2c2_data_clk {
bias-disable;
};

Instead of replicating the hierarchy in the board dts files, like this:

/ {
soc@0 {
pinctrl@f100000 {
qup-i2c2-data-clk {
bias-disable;;
};
};
};
};

(and, of course, you could replicate parts of the hierarchy too).

It was attempted back in 8974 times, but things fell apart pretty quickly, as typos went unnoticed en masse and it resulted in various regressions from creating dead, useless code to things not working for supposedly no reason. Labels make it harder to mess things up like this, as referencing a non-existent one will simply break compilation. Sadly, they still don't fix typos in properties/compatibles, but we have dt-schema for that.



When you avoid replicating things then it really causes everything to
become scattered / disorganized and I think there's a benefit to
trying to enforce some type of ordering.

Going back to the 8974 example, we've come a really really really long way (you can compare with [1] for example), but yes, we can probably still do a bit better.




The present solution, in my opinion, causes more disarray as you first
have to think about what is the change against and then find it in the
corresponding subsection instead of thinking of it as a complete
quote-on-quote diff against the parent DTSIs.
It's a fair opinion. I'd be interested to know if others feel the same
way. In general it feels like a style decision for the people working
on these boards, subject to the approval of the Qualcomm tree
maintainer(s).

Sure, my opinion is not end-all-be-all.




Plus, most DTs don't split
it like that.
I will say that it's hard to compare the trogdor (and now herobrine)
situation with most other ARM boards out there. There are _a lot_ of
different variants and revisions and it's, IMO, more art than science
in trying to balance all of the tradeoffs between duplicating code and
ending up with unreadable spaghetti. I won't claim that we made the
right tradeoff in every case, but so far experience on trogdor has
been that things ended up being fairly understandable I think?

I think the biggest problem for these devices is that often a single revision/model has something very different to others, which makes supporting it require more mess on both sides.. I think it is managed quite sanely, but I also think that /delete-node/ could be used more often instead of copying the same code in n places. While not at the same scale, we have to deal with this mess on Xperias where they are all based on per-SoC common boards and it makes little sense to keep them separate, but unifying them requires some clever positioning to commonize as much as possible.


Konrad


[1] https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/arch/arm/boot/dts/qcom-msm8974.dtsi?h=v5.10.117


-Doug