linux-kernel - Re: [PATCH] ARM: realview: remove eb-mp clcd IRQ

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Date:   Tue, 9 Jan 2018 15:47:37 +0100
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Robin Murphy <robin.murphy@....com>
Cc:     Arnd Bergmann <arnd@...db.de>, Mark Rutland <mark.rutland@....com>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>, Rob Herring <robh+dt@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] ARM: realview: remove eb-mp clcd IRQ

On Mon, Jan 8, 2018 at 5:31 PM, Robin Murphy <robin.murphy@....com> wrote:
> On 21/12/17 22:08, Linus Walleij wrote:

>> I do think the reference design has a character LCD, and I
>> do think it has an interrupt, it's just undocumented so
>> someone with this board would have to test it manually
>> to figure out which line it is. Whoever uses this design
>> will get to it if ever.
>
> FWIW the EB baseboard is *physically* the same regardless of the CPU, it's
> just flashed with a Core-Tile-specific FPGA bitstream.

Aha I always wondered how that works :)

> I've just tried
> firing up an 11MPCore one, and indeed the character LCD does light up with
> the kernel version. I can't convince the recalcitrant beast to actually get
> to userspace, though, so I can't confirm what the interrupt's deal is.

Yeah the driver survives fine without an IRQ too so it just works ...

> The baseboard manual (DUI0303E) says it's interrupt 22 on the board-level
> secondary GICs, and since neither the CT11MP nor its corresponding FPGA
> (AN152) mention any alternate routing direct to the Core Tile GIC, I'd guess
> it probably still is. On the other hand, though, it also says this:
>
>   "... However this interrupt signal is reserved for future use and you
>    must use a polling routine instead of an interrupt service routine."
>
> So maybe it's appropriate to just remove the interrupt everywhere :/

Hm I don't think there will be future releases of these EB
boards anytime soon, so I suspect we could just add it.

But as it works fine without IRQ we can just leave it as well.

Yours,
Linus Walleij