Re: "Virtual" Interrupts -- Need help please

[Daniel Santos <danielfsantos@att.net>]

On 09/07/2013 07:52 PM, Guenter Roeck wrote:
> On 09/07/2013 05:19 PM, Daniel Santos wrote:
>> I've posted a number of requests for aid on this and have gotten very 
>> little responses and none that were helpful. I have spent at least 24 
>> hours of research time on this and just a little direction from 
>> somebody who knows this subsystem can help me immensely as the IRQ 
>> subsystem is new to me.
>>
>> This is for the MCP2210 driver (a USB to SPI/GPIO bridge) and my 
>> driver is the first of its class for the Linux kernel, giving me less 
>> to look at as an example.  I intend to use standard drivers for 
>> whatever I have connected at the other end.  For this to work, I need 
>> to supply interrupts for some of these drivers to work correctly.  
>> How do I do this? Every thing else on this driver is ready to go and 
>> my handler functions for this are empty and waiting for some code.
>>
> Not really. Have a look at https://github.com/groeck/diolan even 
> though the SPI part there
> still isn't working and it is far from being acceptable upstream in 
> its current form.
> It also doesn't support interrupts.

Oh, this is wonderful to know!  While I like breaking new ground, I 
certainly don't enjoy doing it when I'm trying to write my first device 
driver and having to learn so many new things.

>
> It is modeled as mfd driver, which I think you might want to consider 
> as well.
>
>> So do i create an IRQ domain and then call generic_handle_irq() from 
>> my URB complete() function? If so, which type of IRQ Domain is 
>> appropriate for this? Unlike typical platform devices, these are 
>> dynamically added and removed throughout the life of the kernel, 
>> adding to the challenge. So, if I understand correctly, my base IRQ 
>> number needs to be dynamically generated.  How should I manage this?
>>
>> Finally, if you have any example drivers that are doing something 
>> similar, that would be SO very helpful as well!
>>
> There are several drivers in drivers/mfd solving the same problem, ie 
> using
> irq domains to pass interrupts to client drivers. Look for 
> irq_domain_add_simple().
> drivers/mfd/tc3589x.c seems to be a good example.

Ahh, wonderful! I was looking at a lot of the code in mfd, but it 
contains so many things that I don't understand yet, so it's been harder 
to be clear on what the driver is doing and why w/o extensive 
examination & study of the subsystems it's using.  This will help!

>
>> I have some secondary (and less important) questions about how to 
>> integrate this with device drivers that want a DT / open firmware 
>> config (which I know almost nothing about at this time), but that can 
>> wait.
>>
> If you look into the mfd subsystem, you may notice that it handles at 
> least some of the complexity
> of interrupt handling as well as devicetree integration. One more 
> reason to use it.
>
> Guenter

Even better, thank you very much!! If this thing had more EEPROM storage 
I would consider using the OF format for it's settings, but I only have 
256 bytes to play with so I'm using a custom compression/encoding.

I'm hoping to present this for an initial review in a month or so. I'm 
sure you guys will shred it, but I'm excited about it anyway! :)

Thanks again!
Daniel