linux-kernel - Re: [patch V2 04/46] genirq/chip: Use the first chip in irq_chip_compose_msi

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Date:   Wed, 26 Aug 2020 23:19:56 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Marc Zyngier <maz@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        Joerg Roedel <joro@...tes.org>,
        iommu@...ts.linux-foundation.org, linux-hyperv@...r.kernel.org,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Jon Derrick <jonathan.derrick@...el.com>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Wei Liu <wei.liu@...nel.org>,
        "K. Y. Srinivasan" <kys@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Steve Wahl <steve.wahl@....com>,
        Dimitri Sivanich <sivanich@....com>,
        Russ Anderson <rja@....com>, linux-pci@...r.kernel.org,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        xen-devel@...ts.xenproject.org, Juergen Gross <jgross@...e.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Megha Dey <megha.dey@...el.com>,
        Jason Gunthorpe <jgg@...lanox.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        Jacob Pan <jacob.jun.pan@...el.com>,
        Baolu Lu <baolu.lu@...el.com>,
        Kevin Tian <kevin.tian@...el.com>,
        Dan Williams <dan.j.williams@...el.com>
Subject: Re: [patch V2 04/46] genirq/chip: Use the first chip in irq_chip_compose_msi_msg()

On Wed, Aug 26 2020 at 20:50, Marc Zyngier wrote:
> On Wed, 26 Aug 2020 12:16:32 +0100,
> Thomas Gleixner <tglx@...utronix.de> wrote:
>> ---
>> V2: New patch. Note, that this might break other stuff which relies on the
>>     current behaviour, but the hierarchy composition of DT based chips is
>>     really hard to follow.
>
> Grepping around, I don't think there is any occurrence of two irqchips
> providing irq_compose_msi() that can share a hierarchy on any real
> system, so we should be fine. Famous last words.

Knocking on wood :)

>>  #ifdef	CONFIG_IRQ_DOMAIN_HIERARCHY
>> -	for (; data; data = data->parent_data)
>> -#endif
>> -		if (data->chip && data->chip->irq_compose_msi_msg)
>> +	for (; data; data = data->parent_data) {
>> +		if (data->chip && data->chip->irq_compose_msi_msg) {
>>  			pos = data;
>> +			break;
>> +		}
>> +	}
>> +#else
>> +	if (data->chip && data->chip->irq_compose_msi_msg)
>> +		pos = data;
>> +#endif
>>  	if (!pos)
>>  		return -ENOSYS;
>
> Is it just me, or is this last change more complex than it ought to
> be?

Kinda.

> diff --git a/kernel/irq/chip.c b/kernel/irq/chip.c
> index 857f5f4c8098..25e18b73699c 100644
> --- a/kernel/irq/chip.c
> +++ b/kernel/irq/chip.c
> @@ -1544,7 +1544,7 @@ int irq_chip_compose_msi_msg(struct irq_data *data, struct msi_msg *msg)
>  	struct irq_data *pos = NULL;
>  
>  #ifdef	CONFIG_IRQ_DOMAIN_HIERARCHY
> -	for (; data; data = data->parent_data)
> +	for (; data && !pos; data = data->parent_data)
>  #endif
>  		if (data->chip && data->chip->irq_compose_msi_msg)
>  			pos = data;
>
> Though the for loop in a #ifdef in admittedly an acquired taste...

Checking !pos is simpler obviously. That doesn't make me hate the loop
in the #ifdef less. :)

What about the below?

Thanks,

        tglx
---
--- a/kernel/irq/internals.h
+++ b/kernel/irq/internals.h
@@ -473,6 +473,15 @@ static inline void irq_domain_deactivate
 }
 #endif
 
+static inline struct irq_data *irqd_get_parent_data(struct irq_data *irqd)
+{
+#ifdef CONFIG_IRQ_DOMAIN_HIERARCHY
+	return irqd->parent_data;
+#else
+	return NULL;
+#endif
+}
+
 #ifdef CONFIG_GENERIC_IRQ_DEBUGFS
 #include <linux/debugfs.h>
 
--- a/kernel/irq/chip.c
+++ b/kernel/irq/chip.c
@@ -1541,18 +1541,17 @@ EXPORT_SYMBOL_GPL(irq_chip_release_resou
  */
 int irq_chip_compose_msi_msg(struct irq_data *data, struct msi_msg *msg)
 {
-	struct irq_data *pos = NULL;
+	struct irq_data *pos;
 
-#ifdef	CONFIG_IRQ_DOMAIN_HIERARCHY
-	for (; data; data = data->parent_data)
-#endif
+	for (pos = NULL; !pos && data; data = irqd_get_parent_data(data)) {
 		if (data->chip && data->chip->irq_compose_msi_msg)
 			pos = data;
+	}
+
 	if (!pos)
 		return -ENOSYS;
 
 	pos->chip->irq_compose_msi_msg(pos, msg);
-
 	return 0;
 }