linux-kernel - Re: [PATCH v5 4/5] PCI: iproc: Add iProc PCIe MSI support

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Date:	Fri, 04 Dec 2015 18:01:42 +0000
From:	Marc Zyngier <marc.zyngier@....com>
To:	Ray Jui <rjui@...adcom.com>, Bjorn Helgaas <bhelgaas@...gle.com>
CC:	Arnd Bergmann <arnd@...db.de>, Hauke Mehrtens <hauke@...ke-m.de>,
	linux-kernel@...r.kernel.org,
	bcm-kernel-feedback-list@...adcom.com, linux-pci@...r.kernel.org
Subject: Re: [PATCH v5 4/5] PCI: iproc: Add iProc PCIe MSI support

On 04/12/15 17:35, Ray Jui wrote:
> This patch adds PCIe MSI support for both PAXB and PAXC interfaces on
> all iProc based platforms
> 
> The iProc PCIe MSI support deploys an event queue based implementation.
> Each event queue is serviced by a GIC interrupt and can support up to 64
> MSI vectors. Host memory is allocated for the event queues, and each event
> queue consists of 64 word-sized entries. MSI data is written to the
> lower 16-bit of each entry, whereas the upper 16-bit of the entry is
> reserved for the controller for internal processing
> 
> Each event queue is tracked by a head pointer and tail pointer. Head
> pointer indicates the next entry in the event queue to be processed by
> the driver and is updated by the driver after processing is done.
> The controller uses the tail pointer as the next MSI data insertion
> point. The controller ensures MSI data is flushed to host memory before
> updating the tail pointer and then triggering the interrupt
> 
> MSI IRQ affinity is supported by evenly distributing the interrupts to
> each CPU core. MSI vector is moved from one GIC interrupt to another in
> order to steer to the target CPU
> 
> Therefore, the actual number of supported MSI vectors is:
> 
> M * 64 / N
> 
> where M denotes the number of GIC interrupts (event queues), and N
> denotes the number of CPU cores
> 
> This iProc event queue based MSI support should not be used with newer
> platforms with integrated MSI support in the GIC (e.g., giv2m or
> gicv3-its)
> 
> Signed-off-by: Ray Jui <rjui@...adcom.com>
> Reviewed-by: Anup Patel <anup.patel@...adcom.com>
> Reviewed-by: Vikram Prakash <vikramp@...adcom.com>
> Reviewed-by: Scott Branden <sbranden@...adcom.com>

Good thing I didn't reply on v4!

Reviewed-by: Marc Zyngier <marc.zyngier@....com>

	M.
-- 
Jazz is not dead. It just smells funny...
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