linux-kernel - Re: [PATCH 03/12] mtd: nand: omap: Move IRQ handling from GPMC to NAND driver

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Date:	Mon, 13 Jul 2015 13:04:30 +0300
From:	Roger Quadros <rogerq@...com>
To:	Tony Lindgren <tony@...mide.com>
CC:	<dwmw2@...radead.org>, <computersforpeace@...il.com>,
	<bcousson@...libre.com>, <ezequiel@...guardiasur.com.ar>,
	<linux-mtd@...ts.infradead.org>, <linux-omap@...r.kernel.org>,
	<devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 03/12] mtd: nand: omap: Move IRQ handling from GPMC to
 NAND driver

Tony,

On 13/07/15 10:10, Tony Lindgren wrote:
> * Roger Quadros <rogerq@...com> [150710 05:26]:
>> Since the Interrupt Events are used only by the NAND driver,
>> there is no point in managing the Interrupt registers
>> in the GPMC driver and complicating it with irqchip modeling.
> 
> I don't think it's a good idea to allow external drivers to
> tinker directly with GPMC registers. How about just set up GPMC
> as an irqchip for the edge detection interrupts?
> 
> I think we already have devices with multiple NAND chips. And
> there's nothing stopping other drivers from using the edge
> detection interrupts.

OK. The GPMC_IRQ registers manage 2 NAND specific interrupts
(terminalcount and fifo) and 'n' WAIT pin edge interrupts.

So we can model this as a irqchip with 'n + 2' interrupts.

We need to take care that if a GPMC chip select needs a
wait pin then it can't be used as a generic interrupt.

We need to get rid of omap_dev_ready() in nand/omap2.c as
it accesses the GPMC_STATUS register directly. Plus it is
hard coded to only monitor wait0 pin.

What is the best map we should use for irqchip?
Some Socs have 4 WAIT pins, some have 3 and some have 2.

Should we start with 0,1,2, for the wait pins and use the next
available free one for the NAND?

cheers,
-roger
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