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

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Message-ID: <55A3BEBC.8060909@ti.com>
Date:	Mon, 13 Jul 2015 16:35:56 +0300
From:	Roger Quadros <rogerq@...com>
To:	nick <xerofoify@...il.com>, Tony Lindgren <tony@...mide.com>
CC:	<devicetree@...r.kernel.org>, <computersforpeace@...il.com>,
	<linux-kernel@...r.kernel.org>, <linux-mtd@...ts.infradead.org>,
	<ezequiel@...guardiasur.com.ar>, <bcousson@...libre.com>,
	<linux-omap@...r.kernel.org>, <dwmw2@...radead.org>
Subject: Re: [PATCH 03/12] mtd: nand: omap: Move IRQ handling from GPMC to
 NAND driver

On 13/07/15 16:32, nick wrote:
> 
> 
> On 2015-07-13 09:21 AM, Roger Quadros wrote:
>> On 13/07/15 16:15, nick wrote:
>>>
>>>
>>> On 2015-07-13 09:12 AM, Roger Quadros wrote:
>>>> On 13/07/15 16:03, nick wrote:
>>>>>
>>>>>
>>>>> On 2015-07-13 09:01 AM, Tony Lindgren wrote:
>>>>>> * nick <xerofoify@...il.com> [150713 05:54]:
>>>>>>> On 2015-07-13 08:40 AM, Tony Lindgren wrote:
>>>>>>>> * Roger Quadros <rogerq@...com> [150713 03:07]:
>>>>>>>>  
>>>>>>>>> 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,
>>>>>>>
>>>>>>> Is that a good idea as to my knowledge of OMAP platforms that register is hardware
>>>>>>> dependent and therefore that may be an issue unless your idea is to create device
>>>>>>> tables like the way they do in the nand subsystems to support various vendor's 
>>>>>>> nand flash expect here for the pins on OMAP SOCs.
>>>>>>
>>>>>> Do you mean mapping irqs based on the GPMC_IRQSTATUS register
>>>>>> bits? If so, that's pretty much how all the GPIO drivers
>>>>>> handle them. We can have a SoC specific irqmask of the valid
>>>>>> bits passed from the dts files, and if necessary we can also
>>>>>> add custom SoC specific IRQ handlers to the GPMC driver if
>>>>>> needed.
>>>>>>
>>>>>> The idea is that the NAND driver can just request the irq
>>>>>> from the GPMC driver and do whatever it wants with the
>>>>>> interrupt.
>>>>>>
>>>>>> Regards,
>>>>>>
>>>>>> Tony
>>>>>>
>>>>> Tony,
>>>>> That is what I was hoping the code was doing. So what appears to be the problem with the 
>>>>> patches related to irq requesting from the GPMC driver.
>>>>> Cheers,
>>>>> Nick 
>>>>>
>>>>
>>>> The problem with this patch is that it expects GPMC_IRQ registers
>>>> to be accessible by the NAND driver and looses the 2 to 4 pins
>>>> of WAIT pin edge detection interrupt capability if it is needed
>>>> for generic use. (not NAND/GPMC memory specific)
>>>>
>>>> cheers,
>>>> -roger
>>>>
>>> I am not sure if this is possible with OMAP boards but can we split the pins
>>> into 1 or 2 for NAND/GPMC memory specific and use the others for WAIT interrupt
>>> capability.
>>> Nick
>>>
>> Yes if the wait pins are not used for NAND/GPMC memory then they can be used
>> as generic edge detect interrupt or probably even a GPI.
>> I don't see what would prevent it.
>>
>> I'm not sure if anyone will dare to use them though as they weren't originally meant
>> for that use and none of the existing kernels support that. So it is really a
>> chicken and egg situation here. :)
>>
>> But I see value in doing it the way Tony says cause it is much cleaner to specify
>> which interrupt (or wait pin) you want for NAND use.
>>
>> cheers,
>> -roger
>>
> I would also have to agree with Tony about this issue and feel his solution 
> seems fine. However why don't recent kernel's support this feature?
> Nick 
> 

kernel supports the feature but OMAP GPMC/NAND driver never supported it because
nobody implemented it.

cheers,
-roger
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