linux-kernel - Re: [Patch Part2 v3 15/24] x86, MSI: Use hierarchy irqdomain to manage MSI interrupts

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Date:	Wed, 29 Oct 2014 10:19:15 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Jiang Liu <jiang.liu@...ux.intel.com>
cc:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Randy Dunlap <rdunlap@...radead.org>,
	Yinghai Lu <yinghai@...nel.org>,
	Borislav Petkov <bp@...en8.de>,
	Grant Likely <grant.likely@...aro.org>,
	Marc Zyngier <marc.zyngier@....com>,
	Yingjoe Chen <yingjoe.chen@...iatek.com>, x86@...nel.org,
	Joerg Roedel <joro@...tes.org>,
	Matthias Brugger <matthias.bgg@...il.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Tony Luck <tony.luck@...el.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
	linux-acpi@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	iommu@...ts.linux-foundation.org
Subject: Re: [Patch Part2 v3 15/24] x86, MSI: Use hierarchy irqdomain to
 manage MSI interrupts

On Wed, 29 Oct 2014, Jiang Liu wrote:
> On 2014/10/29 5:37, Thomas Gleixner wrote:
> > On Tue, 28 Oct 2014, Jiang Liu wrote:
> >> +static int msi_set_affinity(struct irq_data *data, const struct cpumask *mask,
> >> +			    bool force)
> >> +{
> >> +	struct irq_data *parent = data->parent_data;
> >> +	int ret;
> >>  
> >> -	msg.data &= ~MSI_DATA_VECTOR_MASK;
> >> -	msg.data |= MSI_DATA_VECTOR(cfg->vector);
> >> -	msg.address_lo &= ~MSI_ADDR_DEST_ID_MASK;
> >> -	msg.address_lo |= MSI_ADDR_DEST_ID(dest);
> >> +	ret = parent->chip->irq_set_affinity(parent, mask, force);
> >> +	/* No need to reprogram MSI registers if interrupt is remapped */
> >> +	if (ret >= 0 && !msi_irq_remapped(data)) {
> >> +		struct msi_msg msg;
> >>  
> >> -	__write_msi_msg(data->msi_desc, &msg);
> >> +		__get_cached_msi_msg(data->msi_desc, &msg);
> >> +		msi_update_msg(&msg, data);
> >> +		__write_msi_msg(data->msi_desc, &msg);
> >> +	}
> > 
> > I'm not too happy about the msi_irq_remapped() conditional here. It
> > violates the whole concept of domain stacking somewhat.
> > 
> > A better separation would be to add a callback to the irq chip:
> > 
> >   	void (*irq_write_msi_msg)(struct irq_data *data, struct msi_desc *msi_desc, bool cached);
> > 
> > and change this code to:
> > 
> >     	if (ret >= 0)
> > 	   	parent->chip->irq_write_msi_msg(parent, data->msi-desc, true);
> >   
> Hi Thomas,
> 	Thanks for your great suggestion and I have worked out a draft
> patch to achieve what you want:)
> 	I have made following changes to irq core to get rid of remapped
> irq logic from msi.c:
> 1) Add IRQ_SET_MASK_OK_DONE in addition to IRQ_SET_MASK_OK and
> IRQ_SET_MASK_OK_NOCOPY. IRQ_SET_MASK_OK_DONE is the same as
> IRQ_SET_MASK_OK for irq core and indicates to stacked irqchip that
> parent irqchips have done all work and skip any handling in descendant
> irqchips.
> 2) Add int (*irq_compose_msi_msg)(struct irq_data *data, struct msi_msg
> *msg) into struct irq_chip. I'm still hesitating to return void or int
> here. By returning void, irq_chip_compose_msi_msg() will be simpler,
> but it loses flexibility.

void should be sufficient. If the chip advertises this function it
better can provide a proper msi msg :)
 
> With above changes to core, we could remove all knowledge of irq
> remapping from msi.c and the irq remapping interfaces get simpler too.
> Please refer to following patch for details. The patch passes basic
> booting tests with irq remapping enabled. If it's OK, I will fold
> it into the patch set.

Yes. That looks reasonable. 
 
> IOAPIC runs into the same situation, but I need some more time
> to find a solution:)

I'm sure you will!

Thanks,

	tglx
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