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

[nick <xerofoify@gmail.com>]

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.
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
>>>>
>>>
>>> ______________________________________________________
>>> Linux MTD discussion mailing list
>>> http://lists.infradead.org/mailman/listinfo/linux-mtd/
>>>

______________________________________________________
Linux MTD discussion mailing list
http://lists.infradead.org/mailman/listinfo/linux-mtd/