linux-kernel - Re: [patch 08/16] genirq: Introduce callback irq_chip.irq_write_msi

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Message-ID: <546C3F55.3090301@huawei.com>
Date:	Wed, 19 Nov 2014 14:57:25 +0800
From:	"Yun Wu (Abel)" <wuyun.wu@...wei.com>
To:	Thomas Gleixner <tglx@...utronix.de>
CC:	Jiang Liu <jiang.liu@...ux.intel.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	"Grant Likely" <grant.likely@...aro.org>,
	Marc Zyngier <marc.zyngier@....com>,
	Yingjoe Chen <yingjoe.chen@...iatek.com>,
	Yijing Wang <wangyijing@...wei.com>
Subject: Re: [patch 08/16] genirq: Introduce callback irq_chip.irq_write_msi_msg

On 2014/11/18 22:32, Thomas Gleixner wrote:

> On Tue, 18 Nov 2014, Yun Wu (Abel) wrote:
> 
> Can you please trim the messages when you're replying?
> 
>> The above you described is absolutely right, but not the things I want
>> to know. :)
>> Take GICv3 ITS for example, it deals with both PCI and non PCI message
>> interrupts. IIUC, several irq_chips need to be implemented in the ITS
>> driver (i.e. pci_msi_chip, A_msi_chip and B_msi_chip). What should we
>> do to the ITS driver if new MSI-capable devices come out?
> 
> You seem to miss the stacking here
> 
> PCI-MSI	->
> A-MSI	->   ITS  -> GIC
> B-MSI	->
> 
> So each of the device types has its own MSI controller. Each of them
> will have their own callbacks and are backed by the underlying ITS/GIC
> implementation.

Yes, this hits the key point. Once a new device type becomes available,
we need to add pieces of code outside the new device's driver to make
it work, which in my opinion is due to lack of core infrastructure.
More specifically, the core infrastructure needs to support mechanism
of MSI, not the various types of devices.

> 
> And that's the only sensible solution.
> 

It's sensible, but not perfect.
What I suggested is to add a generic layer:

PCI-MSI	->
A-MSI	-> (generic layer) -> ITS -> GICR
B-MSI	->

The PCI/A/B/... passes its hardware properties to the generic layer which
gets configurations ready by calling ITS's domain/chip callbacks. When
a new device type arrives, the only thing need to do is to implement the
driver of that device, with nothing to do with the generic layer or ITS.

Thanks,
	Abel

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