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

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Date:	Wed, 29 Jul 2015 15:06:45 +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 15:40, Tony Lindgren wrote:
> * Roger Quadros <rogerq@...com> [150713 03:07]:
>> 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.
> 
> OK

For the wait pins irqchip is not sufficient and it needs to be gpiochip
with irqchip. Waitpin status can be read from GPIO_STATUS register.

Just getting the interrupt is not enough and we want to know if the
line is high or low. That is how nand->dev_ready works.

How about having 2 IRQ domains?
One is irqchip with 2 interrupts (terminalcount and fifo) and second is
gpiochip + irqchip for the n wait pins.

The nand driver can then be modified to use GPIO to get Read/Busy
pin status from the wait pin.

cheers,
-roger

>  
>> 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.
> 
> OK
>  
>> 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?
> 
> Maybe we can just use the bits defined for each SoC in the
> GPMC_IRQSTATUS register for the mapping?  
> Regards,
> 
> Tony
> 
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