Re: [PATCH] Input: tsc200x: Drop hard-coded IRQ edge

On Mon, May 10, 2021 at 7:39 PM Dmitry Torokhov
[off-list ref] wrote:

On Mon, May 10, 2021 at 11:29:08AM +0200, Linus Walleij wrote:

quoted

On Mon, May 10, 2021 at 2:22 AM Dmitry Torokhov
[off-list ref] wrote:

quoted

On Mon, May 10, 2021 at 01:38:30AM +0200, Linus Walleij wrote:

quoted

quoted

This edge setting should come from the device tree not
the driver. Also, most device trees sets this to the
falling edge, which is contradictory to what is hardcoded.

I see there are 2 possibilities:

1. The driver has never worked
2. DT interrupt annotation is wrong.

It would be nice to know if we are dealing with 1 or 2, as in case of #2
we need to adjust DTSes before this patch can be applied.

I looked closer and unfortunately the mess and confusion
is bizarre.

The DTS files we know of are:
arch/arm/boot/dts/am3517-som.dtsi - rising
arch/arm/boot/dts/imx28-tx28.dts - falling
arch/arm/boot/dts/imx35-eukrea-cpuimx35.dtsi - low
arch/arm/boot/dts/imx51-eukrea-cpuimx51.dtsi - low
arch/arm/boot/dts/imx53-tx53-x03x.dts - falling
arch/arm/boot/dts/imx6q-dhcom-som.dtsi - falling
arch/arm/boot/dts/imx6qdl-tx6.dtsi - none
arch/arm/boot/dts/imx6ul-tx6ul.dtsi - none
arch/arm/boot/dts/imx7d-nitrogen7.dts - falling
arch/arm/boot/dts/logicpd-som-lv.dtsi - rising
arch/arm/boot/dts/logicpd-torpedo-baseboard.dtsi - rising
arch/arm/boot/dts/omap3-gta04.dtsi - falling
arch/arm/boot/dts/omap3-n900.dts - rising
arch/arm/boot/dts/omap4-var-som-om44.dtsi - low
arch/arm/boot/dts/stm32mp15xx-dhcom-som.dtsi - falling

We can assume that some of this is the result of board
engineers introducing inverters on the board as is custom,
so the flags are actually correct when set to falling, just
that we don't model the inverter.

In the case of imx6qdl-tx6 and imx6ul-tx6ul with "none" IRQ
type I assume this flag in the driver is actually necessary
for the device to work at all.

In the cases where rising is set, the addition of the flag is
plain tautology, just setting what is already set.

In the cases where falling are set the interrupts will arrive
on both edges (if the hardware can provide that, which is
not always the case) and as a result fire twice as many
interrupts as they should, probably with zero effect on the
second IRQ, just reporting nothing.

That is not how we set up interrupts though. We only use
platform-supplied trigger if caller did not specify trigger when calling
request_irq().  From kernel/irq/manage.c::__setup_irq():

        /*
         * If the trigger type is not specified by the caller,
         * then use the default for this interrupt.
         */
        if (!(new->flags & IRQF_TRIGGER_MASK))
                new->flags |= irqd_get_trigger_type(&desc->irq_data);

So in our case, since driver specified IRQF_TRIGGER_RISING it is how
interrupt line was configured, and what was in DTS had no effect.

quoted

The combination with active low is weird. I wonder what
happens there.

I am just confused now and have no idea what to do about
it...

But I just CC all the Freescale and OMAP people who
seem to maintain these DTS files so they can clarify
how well assigned these edges, none and active low (!)
IRQs are.

Hopefully they can confirm how the controller is wired on their boards
and then we can correct invalid DTSes and then finally apply your patch
to the driver.

I reviewed the Logicpd Torpedo (DM3730) and there isn't an interter.
I changed the device tree entry for it to falling edge instead and
rising, and it continued to work perfectly.

I'll review both the schematics and test the am3517-evm and the
logicpd som-lv, but I am going to expect the same results since
they'll all basically copy-paste of each other.

Once I've completed my analysis, I'll post device tree updates for all
the logicpd stuff.

adam

Thanks.

--
Dmitry