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Date:   Thu, 6 Oct 2022 20:25:16 +1100 (AEDT)
From:   Finn Thain <fthain@linux-m68k.org>
To:     Christophe Leroy <christophe.leroy@csgroup.eu>
cc:     Michael Schmitz <schmitzmic@gmail.com>,
        "James E.J. Bottomley" <jejb@linux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@oracle.com>,
        linux-kernel@vger.kernel.org, linux-scsi@vger.kernel.org
Subject: Re: [PATCH] scsi: mac_scsi: Replace NO_IRQ by 0
In-Reply-To: <f11593e75ba2e18e3b76989255cbb2e53a0213b4.1665034244.git.christophe.leroy@csgroup.eu>
Message-ID: <5fb75ac2-678a-dd6e-2e68-7485b2d2ce5f@linux-m68k.org>
References: <f11593e75ba2e18e3b76989255cbb2e53a0213b4.1665034244.git.christophe.leroy@csgroup.eu>
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On Thu, 6 Oct 2022, Christophe Leroy wrote:

> NO_IRQ is used to check the return of irq_of_parse_and_map().
> 
> On some architecture NO_IRQ is 0, on other architectures it is -1.
> 

Yes. The core NCR5380 driver is used on ARM etc. where NO_IRQ is -1 as 
well as on powerpc where it is 0.

> irq_of_parse_and_map() returns 0 on error, independent of NO_IRQ.
> 
> So use 0 instead of using NO_IRQ.
> 

Sorry, I must be missing something.

You seem to be saying that this driver could be re-used in the context of 
openfirmware/device trees if it avoided using the NO_IRQ. Do I have that 
right?

Or are you changing NO_IRQ semantics tree-wide for some reason explained 
somewhere else?

If it is the former, shouldn't you reverse the comment in 
arch/powerpc/include/asm/irq.h, which says the macro is to be used in the 
way this driver (and others) use it?

If it is the latter, shouldn't you address the use of NO_IRQ in the core 
NCR5380 driver rather than just this wrapper?

Moreover, wouldn't it make more sense to fix the callers of 
irq_of_parse_and_map(), since they appear to be abusing the NO_IRQ macro?

For example, drivers/ata/sata_dwc_460ex.c actually does #define NO_IRQ 0 
and then expects irq_of_parse_and_map() will somehow use the same value to 
mean the same thing...

> Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
> ---
>  drivers/scsi/mac_scsi.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/scsi/mac_scsi.c b/drivers/scsi/mac_scsi.c
> index 2e511697fce3..e4df2b501e8b 100644
> --- a/drivers/scsi/mac_scsi.c
> +++ b/drivers/scsi/mac_scsi.c
> @@ -478,7 +478,7 @@ static int __init mac_scsi_probe(struct platform_device *pdev)
>  	if (irq)
>  		instance->irq = irq->start;
>  	else
> -		instance->irq = NO_IRQ;
> +		instance->irq = 0;
>  
>  	hostdata = shost_priv(instance);
>  	hostdata->base = pio_mem->start;
> @@ -495,7 +495,7 @@ static int __init mac_scsi_probe(struct platform_device *pdev)
>  	if (error)
>  		goto fail_init;
>  
> -	if (instance->irq != NO_IRQ) {
> +	if (instance->irq) {
>  		error = request_irq(instance->irq, macscsi_intr, IRQF_SHARED,
>  		                    "NCR5380", instance);
>  		if (error)
> @@ -514,7 +514,7 @@ static int __init mac_scsi_probe(struct platform_device *pdev)
>  	return 0;
>  
>  fail_host:
> -	if (instance->irq != NO_IRQ)
> +	if (instance->irq)
>  		free_irq(instance->irq, instance);
>  fail_irq:
>  	NCR5380_exit(instance);
> @@ -528,7 +528,7 @@ static int __exit mac_scsi_remove(struct platform_device *pdev)
>  	struct Scsi_Host *instance = platform_get_drvdata(pdev);
>  
>  	scsi_remove_host(instance);
> -	if (instance->irq != NO_IRQ)
> +	if (instance->irq)
>  		free_irq(instance->irq, instance);
>  	NCR5380_exit(instance);
>  	scsi_host_put(instance);
>