linux-kernel - Re: [PATCH v2] gpio: Add Avionic Design N-bit GPIO expander support

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Message-ID: <CACRpkdZDQLRDzxmkcrMQX+ZGwSgMwtBsD4sPr_S2jOyft1L37Q@mail.gmail.com>
Date:	Mon, 6 Aug 2012 08:39:24 +0200
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Thierry Reding <thierry.reding@...onic-design.de>
Cc:	Grant Likely <grant.likely@...retlab.ca>,
	Arnd Bergmann <arnd@...db.de>, linux-kernel@...r.kernel.org,
	devicetree-discuss@...ts.ozlabs.org,
	Linus Walleij <linus.walleij@...ricsson.com>,
	Rob Herring <rob.herring@...xeda.com>,
	Wolfram Sang <w.sang@...gutronix.de>
Subject: Re: [PATCH v2] gpio: Add Avionic Design N-bit GPIO expander support

On Mon, Aug 6, 2012 at 7:11 AM, Thierry Reding
<thierry.reding@...onic-design.de> wrote:
> On Sun, Aug 05, 2012 at 12:50:54PM +0200, Linus Walleij wrote:

>> We're working on a goal of a "single zImage" (one unified ARM
>> kernel) which means your platform must be able to handle the
>> case where this is turned on anyway, so I would suggest you
>> drop the optional compile-time IRQ support, just make it
>> optional at runtime instead.
>
> I don't quite understand. Do you want me to add a module parameter to
> make it optional at runtime? Since the driver is now OF only I suppose I
> could make it optional on the interrupt-controller property as well.

No, no module parameter. Just don't register the IRQ domain if there
are not IRQ resources in the device tree, if the interrupt-controller
property is not present I guess?

>> OK but atleast find a way to move this to the probe() function,
>> what happens if the debugfs file is browsed and you run out
>> of memory? Not nice, and you were using this to debug as
>> well...
>
> Alright, I can do that. Alternatively I could probably drop the
> allocations altogether and use local variables within the second loop to
> store the variables:
>
>         for (i = 0; i < num_regs; i++) {
>                 u8 ddr, plr, ier, isr, ptr;
>
>                 err = adnp_read(gpio, GPIO_DDR(gpio) + i, &ddr);
>                 if (err < 0)
>                         goto out;
>
>                 ...
>         }
>
> With the proper locking this shouldn't be a problem. The reason why I
> used the block-wise approach in the first place was that the register
> accesses were more "atomic". Of course without locking this is non-
> sense.

Either approach works, the above seems more elegant though!

Yours,
Linus Walleij
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