[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <CACRpkdaTYAr-7K5_QZh1CyeyA1224obqEB2Sz8UHZmrWcfv+ow@mail.gmail.com>
Date: Wed, 13 May 2015 10:59:30 +0200
From: Linus Walleij <linus.walleij@...aro.org>
To: Gregory Fong <gregory.0xf0@...il.com>
Cc: "linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
Alexandre Courbot <gnurou@...il.com>,
bcm-kernel-feedback-list <bcm-kernel-feedback-list@...adcom.com>,
Brian Norris <computersforpeace@...il.com>,
"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
Florian Fainelli <f.fainelli@...il.com>,
Ian Campbell <ijc+devicetree@...lion.org.uk>,
Kumar Gala <galak@...eaurora.org>,
"linux-arm-kernel@...ts.infradead.org"
<linux-arm-kernel@...ts.infradead.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
Mark Rutland <mark.rutland@....com>,
Pawel Moll <pawel.moll@....com>,
Rob Herring <robh+dt@...nel.org>,
Russell King <linux@....linux.org.uk>
Subject: Re: [PATCH 0/3] GPIO support for BRCMSTB
On Tue, May 12, 2015 at 9:38 PM, Gregory Fong <gregory.0xf0@...il.com> wrote:
> On Tue, May 12, 2015 at 3:59 AM, Linus Walleij <linus.walleij@...aro.org> wrote:
>> On Wed, May 6, 2015 at 10:37 AM, Gregory Fong <gregory.0xf0@...il.com> wrote:
>>
>>> There is only one IRQ for each GIO IP block (i.e. several register banks share
>>> an IRQ). After briefly looking into the generic IRQ chip implementation, it
>>> seemed like in this case that using it would result in the driver being more
>>> complex than necessary because AFAICT it expects a 1:1 mapping of
>>> irq_chip_generic to gpio_chip. It seemed like less of a pain to have a single
>>> irq_chip since we have a single IRQ for all register banks (multiple
>>> gpio_chips). I might be missing something, maybe using a shared IRQ across
>>> multiple irq_chips is easier than I think? Suggestions welcome.
>>
>> What is needed is a 1:1 mapping between GPIO offsets and IRQ
>> offsets.
>>
>> If you just number your GPIOs 0...n and your IRQs 0...n
>> it should work just fine with one irqchip for all banks.
>>
>> What screws things up is likely that the hardware supports
>> 32 lines per bank and not all are used.
>>
>> I suggest you enable 32 line and 32 IRQs per bank,
>> so that hwirq maps nicely 1:1 on the GPIO offsets,
>> then just use the width thing to NACK operations on
>> GPIO lines you are not using. This way you can also
>> decode and warn on spurious IRQs on the unused lines.
>
> For having 32 lines per bank, the big problem here is the upper limit
> of 256 GPIOs.
Which arch is this?
Usually this limit comes from
arch/*/include/asm/gpio.h
For ARM that was bumped to 512 a while back. It is also possible
to define a custom value for your system by defining
ARCH_NR_GPIOS
> Anyway, I don't think I understand IRQ domains and irq_chip_generic
> very well. One possibility _might_ be to use multiple irq_chips.
That is probably not possible if there is just one IRQ for all
banks.
The task of the irqdomain is a 1-to-1 translation from one
hardware numberspace to the Linux IRQ number space.
In your case the hardware IRQ (hwirq) numberspace
should be:
bank0: 0..31
bank1: 32..63
....
bankn: 32*n..32*n+31
I think the gpiolib irqchip code can translate that properly
as it is just a simple 0...x mapping, the irq handler need
some magic to loop over all banks from 0..n though.
Yours,
Linus Walleij
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
Powered by blists - more mailing lists