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

[nick <xerofoify@gmail.com>]

On 2015-07-29 11:12 AM, Roger Quadros wrote:
> On 29/07/15 17:08, nick wrote:
>>
>>
>> On 2015-07-29 09:52 AM, Roger Quadros wrote:
>>> On 29/07/15 15:13, nick wrote:
>>>>
>>>>
>>>> On 2015-07-29 08:06 AM, Roger Quadros wrote:
>>>>> Tony,
>>>>>
>>>>> On 13/07/15 15:40, Tony Lindgren wrote:
>>>>>> * Roger Quadros <rogerq@ti.com> [150713 03:07]:
>>>>>>> Tony,
>>>>>>>
>>>>>>> On 13/07/15 10:10, Tony Lindgren wrote:
>>>>>>>> * Roger Quadros <rogerq@ti.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
>>>>>
>>>> Doesn't OMAP boards support shared IRQs and if so why not share them across one
>>>> IRQ domain if possible to save IRQ domains for other hardware that needs its 
>>>> own IRQ domain. This is just a suggestion through as I don't have the hardware
>>>> spec sheet on me Roger.
>>>
>>> IRQ domain is a virtual abstraction introduced to prevent kernel irq number overlapping
>>> in a single flat domain. I don't see what you can save by domain reuse.
>>> Some memory maybe at most.
>>>
>>> Shared interrupt is something totally different but we're trying to add real
>>> hardware interrupts here. Didn't understand what you will share it with.
>>>
>>> cheers,
>>> -roger
>>>
>> My question then is do these hardware interrupts need to be on their own interrupt line
>> for the CPU or can they share a CPU line as my concern is if possible we may be able to
>> save a interrupt line for other use. I known on Intel CPUs this is a very limited resource
>> but not sure on OMAP based boards if not then just avoid my recommendations.
> 
> It is like adding an external interrupt controller to expand the number of available
> hardware interrupts.
> This interrupt controller will still use the same GPMC IRQ line to propagate the
> irq event upwards.
> 
> cheers,
> -roger
> 
That was my other suggestion for IRQ issues. Would you mind sending me a link to a spec sheet so
I can review your patches better as you stated you wanted me to do this for you.
Nick 
>> Nick 
>>>> Nick 
>>>>>>  
>>>>>>> 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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>>>>> http://lists.infradead.org/mailman/listinfo/linux-mtd/
>>>>>

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