Re: Questions about request_irq and reading PCI_INTERRUPT_LINE

[linux-os]

On Fri, 18 Mar 2005, Le Wen wrote:

> Hi, there,
>
> I have problem to grab video from my ati all-in-wonder card. The card is in a 
> PII Celeron machine with an on board video card (ATI Technologies Inc 3D Rage 
> IIC AGP). there is no monitor connected with the on board video card. I only 
> hook my AIW card with a monitor.
>
> I use km-0.6 from gatos project. I load this km_drv module, but kernel always 
> complains:
>
> km: IRQ 0 busy
>
> I checked code:
>       km_probe(struct pci_dev *dev, const struct pci_device_id *pci_id)
>
> here dev->irq with a value 0.
>
> When km_probe gets called, it try to request an IRQ0 returns a -EBUSY:
>       kms_irq=dev.irq;
>       result=request_irq(kms->irq, handler, SA_SHIRQ, tag, (void *)kms);
>
>       if(result==-EBUSY){
>               printk(KERN_ERR "km: IRQ %ld busy\n", kms->irq);
>               goto fail;
>       }
>
>
> So I tried to get right IRQ number using:
>       u8 myirq;
>       int rtn=pci_read_config_byte(dev,PCI_INTERRUPT_LINE, &myirq);
>       dev->irq=myirq;
>       kms->irq=dev_irq;
>       result=request_irq(kms->irq, handler, SA_SHIRQ, tag, (void *)kms);
>
>       if(result==-EBUSY){
>               printk(KERN_ERR "km: IRQ %ld busy\n", kms->irq);
>               goto fail;
>       }
>       if(result<0){
>               printk(KERN_ERR "km: could not install irq handler: 
> result=%d\n",result);
>               goto fail;
>       }
> But this time I got:
>
> km: kms->irq=24
> km: could not install irq handler: result=-38
>
>
> My questions are:
> 1. I don't know why dev->irq has value of 0?

The PCI interface now needs to be enabled first. The IRQ value
returned is BAD until after one calls pci_enable_device(). This
is a BUG, now considered a FEATURE so it's unlikely to be fixed!
There are lots of people who have encountered this problem
with modules that are not in the "distribution".

> 2. Is an IRQ number of 24 valid for a Intel PII Celeron?

Could be, but it;s probably invalid considering the way you
got it.

> 3. What does this result=-38 mean?

Probably errno 38, i.e., ENOSYS

> Wen, Le

Cheers,
Dick Johnson
Penguin : Linux version 2.6.11 on an i686 machine (5537.79 BogoMips).
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