linux-kernel - Re: [PATCH 2/6] g_NCR5380: Test the IRQ before accepting it

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Date:   Wed, 2 Nov 2016 18:45:26 +1100 (AEDT)
From:   Finn Thain <fthain@...egraphics.com.au>
To:     Ondrej Zary <linux@...nbow-software.org>
cc:     Christoph Hellwig <hch@...radead.org>, linux-scsi@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/6] g_NCR5380: Test the IRQ before accepting it


On Mon, 31 Oct 2016, Ondrej Zary wrote:

> Trigger an IRQ first with a test IRQ handler to find out if it really
> works. Disable the IRQ if not.
> 
> This prevents hang when incorrect IRQ was specified by user.
> 

Once again, how does it cause a hang?

If the user specifies an IRQ, we should trust them. If they don't specify 
an IRQ then probe (as in patch 5/6).

> Signed-off-by: Ondrej Zary <linux@...nbow-software.org>
> ---
>  drivers/scsi/g_NCR5380.c |   44 +++++++++++++++++++++++++++++++++++++++++---
>  1 file changed, 41 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/scsi/g_NCR5380.c b/drivers/scsi/g_NCR5380.c
> index 09c660b..0d1f6ad 100644
> --- a/drivers/scsi/g_NCR5380.c
> +++ b/drivers/scsi/g_NCR5380.c
> @@ -115,6 +115,32 @@ static int NCR5380_probe_irq(struct Scsi_Host *instance)
>  	return irq;
>  }
>  
> +static bool irq_working;
> +
> +static irqreturn_t test_irq(int irq, void *dev_id)
> +{
> +	irq_working = true;
> +	return IRQ_HANDLED;
> +}
> +
> +/* test if the IRQ is working */
> +static int NCR5380_test_irq(struct Scsi_Host *instance, int irq)
> +{
> +	struct NCR5380_hostdata *hostdata = shost_priv(instance);
> +
> +	irq_working = false;
> +	if (request_irq(irq, test_irq, 0, "NCR5380-irqtest", NULL))
> +		return -EBUSY;
> +	NCR5380_trigger_irq(instance);
> +	NCR5380_read(RESET_PARITY_INTERRUPT_REG);
> +	free_irq(irq, NULL);
> +
> +	if (!irq_working)
> +		return -EIO;
> +
> +	return 0;
> +}
> +

IMO the extra complexity is not justified by the possibility of machines 
with misconfigured BIOS or incorrect module parameters.

I don't want another irq probing mechanism. We just got rid of one.

But I won't mind if the SCSI maintainers who know ISA better than I do 
would like to review this.

>  /*
>   * Configure I/O address of 53C400A or DTC436 by writing magic numbers
>   * to ports 0x779 and 0x379.
> @@ -323,9 +349,21 @@ static int generic_NCR5380_init_one(struct scsi_host_template *tpnt,
>  		/* set IRQ for HP C2502 */
>  		if (board == BOARD_HP_C2502)
>  			magic_configure(port_idx, instance->irq, magic);
> -		if (request_irq(instance->irq, generic_NCR5380_intr,
> -				0, "NCR5380", instance)) {
> -			printk(KERN_WARNING "scsi%d : IRQ%d not free, interrupts disabled\n", instance->host_no, instance->irq);
> +		ret = NCR5380_test_irq(instance, instance->irq);
> +		if (ret) {
> +			printk(KERN_WARNING "scsi%d : IRQ%d not %s, interrupts disabled\n",
> +			       instance->host_no, instance->irq,
> +			       (ret == -EBUSY) ? "free" : "working");
> +			instance->irq = NO_IRQ;
> +		}
> +	}
> +
> +	if (instance->irq != NO_IRQ) {
> +		if (request_irq(instance->irq, generic_NCR5380_intr, 0,
> +				"NCR5380", instance)) {
> +			printk(KERN_WARNING "scsi%d : IRQ%d not free, interrupts disabled\n",
> +			       instance->host_no,
> +			       instance->irq);
>  			instance->irq = NO_IRQ;
>  		}
>  	}
> 

--