Message-ID: <564EE04D.8060204@arm.com>
Date:	Fri, 20 Nov 2015 08:56:45 +0000
From:	Marc Zyngier <marc.zyngier@....com>
To:	Ray Jui <rjui@...adcom.com>
CC:	Bjorn Helgaas <bhelgaas@...gle.com>, 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 4/5] PCI: iproc: Add iProc PCIe MSI support

On 19/11/15 01:37, Ray Jui wrote:
> Hi Marc,
> 
> On 11/18/2015 12:48 AM, Marc Zyngier wrote:
>> On Tue, 17 Nov 2015 16:31:54 -0800
>> Ray Jui <rjui@...adcom.com> wrote:
>>
>> Hi Ray,
>>
>> A few comments below.
>>
>>> This patch adds PCIe MSI support for both PAXB and PAXC interfaces on
>>> all iProc based platforms. The patch follows the latest trend in the
>>> kernel to use MSI domain based implementation
>>>
>>> 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>
>>> ---
>>>   drivers/pci/host/Kconfig          |   9 +
>>>   drivers/pci/host/Makefile         |   1 +
>>>   drivers/pci/host/pcie-iproc-msi.c | 434 ++++++++++++++++++++++++++++++++++++++
>>>   drivers/pci/host/pcie-iproc.c     |  19 ++
>>>   drivers/pci/host/pcie-iproc.h     |  12 ++
>>>   5 files changed, 475 insertions(+)
>>>   create mode 100644 drivers/pci/host/pcie-iproc-msi.c
>>>
>>> diff --git a/drivers/pci/host/Kconfig b/drivers/pci/host/Kconfig
>>> index f131ba9..972e906 100644
>>> --- a/drivers/pci/host/Kconfig
>>> +++ b/drivers/pci/host/Kconfig
>>> @@ -126,6 +126,15 @@ config PCIE_IPROC
>>>   	  iProc family of SoCs. An appropriate bus interface driver also needs
>>>   	  to be enabled
>>>
>>> +config PCIE_IPROC_MSI
>>> +	bool "Broadcom iProc PCIe MSI support"
>>> +	depends on ARCH_BCM_IPROC && PCI_MSI
>>> +	select PCI_MSI_IRQ_DOMAIN
>>> +	default ARCH_BCM_IPROC
>>> +	help
>>> +	  Say Y here if you want to enable MSI support for Broadcom's iProc
>>> +	  PCIe controller
>>> +
>>>   config PCIE_IPROC_PLATFORM
>>>   	tristate "Broadcom iProc PCIe platform bus driver"
>>>   	depends on ARCH_BCM_IPROC || (ARM && COMPILE_TEST)
>>> diff --git a/drivers/pci/host/Makefile b/drivers/pci/host/Makefile
>>> index 9d4d3c6..0e4e95e 100644
>>> --- a/drivers/pci/host/Makefile
>>> +++ b/drivers/pci/host/Makefile
>>> @@ -15,6 +15,7 @@ obj-$(CONFIG_PCI_XGENE_MSI) += pci-xgene-msi.o
>>>   obj-$(CONFIG_PCI_LAYERSCAPE) += pci-layerscape.o
>>>   obj-$(CONFIG_PCI_VERSATILE) += pci-versatile.o
>>>   obj-$(CONFIG_PCIE_IPROC) += pcie-iproc.o
>>> +obj-$(CONFIG_PCIE_IPROC_MSI) += pcie-iproc-msi.o
>>>   obj-$(CONFIG_PCIE_IPROC_PLATFORM) += pcie-iproc-platform.o
>>>   obj-$(CONFIG_PCIE_IPROC_BCMA) += pcie-iproc-bcma.o
>>>   obj-$(CONFIG_PCIE_ALTERA) += pcie-altera.o
>>> diff --git a/drivers/pci/host/pcie-iproc-msi.c b/drivers/pci/host/pcie-iproc-msi.c
>>> new file mode 100644
>>> index 0000000..a55c707
>>> --- /dev/null
>>> +++ b/drivers/pci/host/pcie-iproc-msi.c
>>> @@ -0,0 +1,434 @@
>>> +/*
>>> + * Copyright (C) 2015 Broadcom Corporation
>>> + *
>>> + * This program is free software; you can redistribute it and/or
>>> + * modify it under the terms of the GNU General Public License as
>>> + * published by the Free Software Foundation version 2.
>>> + *
>>> + * This program is distributed "as is" WITHOUT ANY WARRANTY of any
>>> + * kind, whether express or implied; without even the implied warranty
>>> + * of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
>>> + * GNU General Public License for more details.
>>> + */
>>> +
>>> +#include <linux/irqchip/chained_irq.h>
>>> +#include <linux/irqdomain.h>
>>> +#include <linux/msi.h>
>>> +#include <linux/of_irq.h>
>>> +#include <linux/of_pci.h>
>>> +#include <linux/pci.h>
>>> +
>>> +#include "pcie-iproc.h"
>>> +
>>> +#define IPROC_MSI_INTS_EN_OFFSET       0x208
>>> +#define IPROC_MSI_INTR_EN_SHIFT        11
>>> +#define IPROC_MSI_INTR_EN              BIT(IPROC_MSI_INTR_EN_SHIFT)
>>> +#define IPROC_MSI_INT_N_EVENT_SHIFT    1
>>> +#define IPROC_MSI_INT_N_EVENT          BIT(IPROC_MSI_INT_N_EVENT_SHIFT)
>>> +#define IPROC_MSI_EQ_EN_SHIFT          0
>>> +#define IPROC_MSI_EQ_EN                BIT(IPROC_MSI_EQ_EN_SHIFT)
>>> +
>>> +#define IPROC_MSI_EQ_MASK              0x3f
>>> +
>>> +/* number of queues in each event queue */
>>> +#define IPROC_MSI_EQ_LEN               64
>>> +
>>> +/* size of each event queue memory region */
>>> +#define EQ_MEM_REGION_SIZE           SZ_4K
>>> +
>>> +/* size of each MSI message memory region */
>>> +#define MSI_MSG_MEM_REGION_SIZE      SZ_4K
>>> +
>>> +enum iproc_msi_reg {
>>> +	IPROC_MSI_EQ_PAGE = 0,
>>> +	IPROC_MSI_EQ_PAGE_UPPER,
>>> +	IPROC_MSI_PAGE,
>>> +	IPROC_MSI_PAGE_UPPER,
>>> +	IPROC_MSI_CTRL,
>>> +	IPROC_MSI_EQ_HEAD,
>>> +	IPROC_MSI_EQ_TAIL,
>>> +	IPROC_MSI_REG_SIZE,
>>> +};
>>> +
>>> +/**
>>> + * iProc event queue based MSI
>>> + *
>>> + * Only meant to be used on platforms without MSI support integrated into the
>>> + * GIC
>>> + *
>>> + * @pcie: pointer to iProc PCIe data
>>> + * @reg_offsets: MSI register offsets
>>> + * @irqs: pointer to an array that contains the interrupt IDs
>>> + * @nirqs: number of total interrupts
>>> + * @has_inten_reg: indicates the MSI interrupt enable register needs to be
>>> + * set explicitly (required for some legacy platforms)
>>> + * @used: bitmap to track usage of MSI
>>> + * @inner_domain: inner IRQ domain
>>> + * @msi_domain: MSI IRQ domain
>>> + * @bitmap_lock: lock to protect access to the IRQ bitmap
>>> + * @n_eq_region: required number of 4K aligned memory region for MSI event
>>> + * queues
>>> + * @n_msi_msg_region: required number of 4K aligned memory region for MSI
>>> + * posted writes
>>> + * @eq_base: pointer to allocated memory region for MSI event queues
>>> + * @msi_base: pointer to allocated memory region for MSI posted writes
>>> + */
>>> +struct iproc_msi {
>>> +	struct iproc_pcie *pcie;
>>> +	const u16 (*reg_offsets)[IPROC_MSI_REG_SIZE];
>>> +	int *irqs;
>>> +	int nirqs;
>>> +	bool has_inten_reg;
>>> +	DECLARE_BITMAP(used, IPROC_PCIE_MAX_NUM_IRQS);
>>> +	struct irq_domain *inner_domain;
>>> +	struct irq_domain *msi_domain;
>>> +	struct mutex bitmap_lock;
>>> +	unsigned int n_eq_region;
>>> +	unsigned int n_msi_msg_region;
>>> +	void *eq_base;
>>> +	void *msi_base;
>>> +};
>>> +
>>> +static const u16
>>> +iproc_msi_reg_paxb[IPROC_PCIE_MAX_NUM_IRQS][IPROC_MSI_REG_SIZE] = {
>>> +	{ 0x200, 0x2c0, 0x204, 0x2c4, 0x210, 0x250, 0x254 },
>>> +	{ 0x200, 0x2c0, 0x204, 0x2c4, 0x214, 0x258, 0x25c },
>>> +	{ 0x200, 0x2c0, 0x204, 0x2c4, 0x218, 0x260, 0x264 },
>>> +	{ 0x200, 0x2c0, 0x204, 0x2c4, 0x21c, 0x268, 0x26c },
>>> +	{ 0x200, 0x2c0, 0x204, 0x2c4, 0x220, 0x270, 0x274 },
>>> +	{ 0x200, 0x2c0, 0x204, 0x2c4, 0x224, 0x278, 0x27c },
>>> +};
>>> +
>>> +static const u16
>>> +iproc_msi_reg_paxc[IPROC_PCIE_MAX_NUM_IRQS][IPROC_MSI_REG_SIZE] = {
>>> +	{ 0xc00, 0xc04, 0xc08, 0xc0c, 0xc40, 0xc50, 0xc60 },
>>> +	{ 0xc10, 0xc14, 0xc18, 0xc1c, 0xc44, 0xc54, 0xc64 },
>>> +	{ 0xc20, 0xc24, 0xc28, 0xc2c, 0xc48, 0xc58, 0xc68 },
>>> +	{ 0xc30, 0xc34, 0xc38, 0xc3c, 0xc4c, 0xc5c, 0xc6c },
>>> +};
>>> +
>>> +static inline u32 iproc_msi_read_reg(struct iproc_msi *msi,
>>> +				     enum iproc_msi_reg reg,
>>> +				     unsigned int eq)
>>> +{
>>> +	struct iproc_pcie *pcie = msi->pcie;
>>> +
>>> +	return readl(pcie->base + msi->reg_offsets[eq][reg]);
>>
>> Do you need the extra barrier implied by readl? readl_relaxed should be
>> enough.
>>
>>> +}
>>> +
>>> +static inline void iproc_msi_write_reg(struct iproc_msi *msi,
>>> +				       enum iproc_msi_reg reg,
>>> +				       int eq, u32 val)
>>> +{
>>> +	struct iproc_pcie *pcie = msi->pcie;
>>> +
>>> +	writel(val, pcie->base + msi->reg_offsets[eq][reg]);
>>
>> Same here for writel vs writel_relaxed.
>>
> 
> I probably do not need the barrier in most cases. But as we are dealing 
> with MSI, I thought it's a lot safer to have the barrier in place so the 
> CPU does not re-order the device register accesses with respect to other 
> memory accesses?
> 
>>> +}
>>> +
>>> +static struct irq_chip iproc_msi_top_irq_chip = {
>>> +	.name = "iProc MSI",
>>> +	.irq_enable = pci_msi_unmask_irq,
>>> +	.irq_disable = pci_msi_mask_irq,
>>> +	.irq_mask = pci_msi_mask_irq,
>>> +	.irq_unmask = pci_msi_unmask_irq,
>>
>> There is no need to provide both enable/disable and mask/unmask. And
>> since pci_msi_{un}mask_irq is the default, you can get rid of these
>> function pointers anyway.
>>
> 
> Got it. Like you said, the mask/unmask callback are defaulted to 
> pci_msi_{un}mask_irq in pci_msi_domain_update_chip_ops, called when the 
> MSI irq domain is created.
> 
> I'll get rid of all the callback assignments here.
> 
>>> +};
>>> +
>>> +static struct msi_domain_info iproc_msi_domain_info = {
>>> +	.flags = MSI_FLAG_USE_DEF_DOM_OPS | MSI_FLAG_USE_DEF_CHIP_OPS |
>>> +		MSI_FLAG_PCI_MSIX,
>>> +	.chip = &iproc_msi_top_irq_chip,
>>> +};
>>> +
>>> +static int iproc_msi_irq_set_affinity(struct irq_data *data,
>>> +				      const struct cpumask *mask, bool force)
>>> +{
>>> +	return -EINVAL;
>>
>> I wish people would stop building stupid HW that prevents proper
>> affinity setting for MSI...
>>
> 
> In fact, there's no reason why the HW should prevent us from setting the 
> MSI affinity. This is currently more of a SW issue that I have not spent 
> enough time figuring out.
> 
> Here's my understanding:
> 
> In our system, each MSI is linked to a dedicated interrupt line 
> connected to the GIC upstream (e.g., the GIC from Cortex A9 in Cygnus). 
> Correct me if I'm wrong, to get the MSI affinity to work, all I need 
> should be propagating the affinity setting to the GIC (the 1-to-1 
> mapping helps simply things quite a bit here)?
> 
> I tried to hook this up with irq_chip_set_affinity_parent. But it looks 
> like the irq chip of the parent domain (i.e., the GIC) is pointing to 
> NULL, and therefore it would crash when dereferencing it to get the 
> irq_set_affinity callback.
> 
> I thought I did everything required by figuring out and linking to the 
> correct parent domain in the iproc_msi_init routine:
> 
> parent_node = of_parse_phandle(node, "interrupt-parent", 0);
> if (!parent_node) {
>        dev_err(pcie->dev, "unable to parse MSI interrupt parent\n");
>        return -ENODEV;
> }
> 
> parent_domain = irq_find_host(parent_node);
> if (!parent_domain) {
>        dev_err(pcie->dev, "unable to get MSI parent domain\n");
>        return -ENODEV;
> }
> 
> ...
> ...
> 
> msi->inner_domain = irq_domain_add_hierarchy(parent_domain, 0,
>                                               msi->nirqs, NULL,
>                                               &msi_domain_ops,
>                                               msi);
> 
> I haven't spent too much time investigating, and am hoping to eventually 
> enable affinity support with an incremental patch in the future when I 
> have more time to investigate.

It fails because you're not implementing a fully stacked system, but
only a partial one (see below).

>>> +}
>>> +
>>> +static void iproc_msi_irq_compose_msi_msg(struct irq_data *data,
>>> +					  struct msi_msg *msg)
>>> +{
>>> +	struct iproc_msi *msi = irq_data_get_irq_chip_data(data);
>>> +	phys_addr_t addr;
>>> +
>>> +	addr = virt_to_phys(msi->msi_base) | (data->hwirq * 4);
>>> +	msg->address_lo = lower_32_bits(addr);
>>> +	msg->address_hi = upper_32_bits(addr);
>>> +	msg->data = data->hwirq;
>>> +}
>>> +
>>> +static struct irq_chip iproc_msi_bottom_irq_chip = {
>>> +	.name = "MSI",
>>> +	.irq_set_affinity = iproc_msi_irq_set_affinity,
>>> +	.irq_compose_msi_msg = iproc_msi_irq_compose_msi_msg,
>>> +};
>>> +
>>> +static int iproc_msi_irq_domain_alloc(struct irq_domain *domain,
>>> +				      unsigned int virq, unsigned int nr_irqs,
>>> +				      void *args)
>>> +{
>>> +	struct iproc_msi *msi = domain->host_data;
>>> +	int i, msi_irq;
>>> +
>>> +	mutex_lock(&msi->bitmap_lock);
>>> +
>>> +	for (i = 0; i < nr_irqs; i++) {
>>> +		msi_irq = find_first_zero_bit(msi->used, msi->nirqs);
>>
>> This is slightly puzzling. Do you really have at most 6 MSIs? Usually,
>> we end up with a larger number of MSIs (32 or 64) multiplexed on top of
>> a small number of wired interrupts. Here, you seem to have a 1-1
>> mapping. Is that really the case?
> 
> Yes, based on the poorly written iProc PCIe arch doc, :), we seem to 
> have 1-1 mapping between each wired interrupt and MSI, with each MSI 
> handled by an event queue, that consists of 64x word entries allocated 
> from host memory (DDR). The MSI data is stored in the low 16-bit of each 
> entry, whereas the upper 16-bit of each entry is reserved for the iProc 
> PCIe controller for its own use.

Based on your description, I have a completely different interpretation
of how your HW works:

You have 4 (or 6) doorbells (the location where your PCI device writes
its MSI), and whatever the device writes ends up in the event queue. I'm
pretty sure the HW doesn't interpret what the device writes at all. The
GIC irqs are just a way to indicate that there is something in one of
the queues.

This means that you wouldn't be limited to 4/6 MSIs, but that you could
actually have a lot more (apparently 16 bits worth of MSIs), and you
could use the doorbell address to change your affinity (one GIC
interrupt per CPU, assuming you don't have more than 4 or 6).

>>
>> If so (and assuming the wired interrupts are always contiguous), you
>> shouldn't represent this as a chained interrupt (a multiplexer), but as
>> a stacked irqchip, similar to what GICv2m does.
>>
> 
> Okay, I think I might be missing something here, but I thought I 
> currently have a stacked irqdomain (chip), i.e., GIC -> inner_domain -> 
> MSI domain?

At the moment, you have one stacked domain (MSI -> iProc) that is used
for a chained irqchip that feeds into the GIC.

What you could do is turning it into a stacked domain (MSI -> iProc ->
GIC), using the fact that you have a 1:1 mapping between your MSIs and
the GIC interrupts. But I'm now questionning that fact.

> And does this imply I should expect 'nr_irqs' in this routine to be 
> always zero and therefore I can get rid of the for loop here (same in 
> the domain free routine)?

It should never be zero. It is likely to be always 1, as it is the
number of contiguous MSIs that have to be allocated in one go, and is
exclusively used for multi-MSI (which you don't claim to support).

>>> +		if (msi_irq < msi->nirqs) {
>>> +			set_bit(msi_irq, msi->used);
>>> +		} else {
>>> +			mutex_unlock(&msi->bitmap_lock);
>>> +			return -ENOSPC;
>>> +		}
>>> +
>>> +		irq_domain_set_info(domain, virq + i, msi_irq,
>>> +				    &iproc_msi_bottom_irq_chip,
>>> +				    domain->host_data, handle_simple_irq,
>>> +				    NULL, NULL);
>>> +	}
>>> +
>>> +	mutex_unlock(&msi->bitmap_lock);
>>> +	return 0;
>>> +}
>>> +
>>> +static void iproc_msi_irq_domain_free(struct irq_domain *domain,
>>> +				      unsigned int virq, unsigned int nr_irqs)
>>> +{
>>> +	struct irq_data *data = irq_domain_get_irq_data(domain, virq);
>>> +	struct iproc_msi *msi = irq_data_get_irq_chip_data(data);
>>> +	unsigned int i;
>>> +
>>> +	mutex_lock(&msi->bitmap_lock);
>>> +
>>> +	for (i = 0; i < nr_irqs; i++) {
>>> +		struct irq_data *data = irq_domain_get_irq_data(domain,
>>> +								virq + i);
>>> +		if (!test_bit(data->hwirq, msi->used)) {
>>> +			dev_warn(msi->pcie->dev, "freeing unused MSI %lu\n",
>>> +				 data->hwirq);
>>> +		} else
>>> +			clear_bit(data->hwirq, msi->used);
>>> +	}
>>> +
>>> +	mutex_unlock(&msi->bitmap_lock);
>>> +	irq_domain_free_irqs_parent(domain, virq, nr_irqs);
>>> +}
>>> +
>>> +static const struct irq_domain_ops msi_domain_ops = {
>>> +	.alloc = iproc_msi_irq_domain_alloc,
>>> +	.free = iproc_msi_irq_domain_free,
>>> +};
>>> +
>>> +static void iproc_msi_enable(struct iproc_msi *msi)
>>> +{
>>> +	struct iproc_pcie *pcie = msi->pcie;
>>> +	int i, eq;
>>> +	u32 val;
>>> +
>>> +	/* program memory region for each event queue */
>>> +	for (i = 0; i < msi->n_eq_region; i++) {
>>> +		phys_addr_t addr =
>>> +			virt_to_phys(msi->eq_base + (i * EQ_MEM_REGION_SIZE));
>>> +
>>> +		iproc_msi_write_reg(msi, IPROC_MSI_EQ_PAGE, i,
>>> +				    lower_32_bits(addr));
>>> +		iproc_msi_write_reg(msi, IPROC_MSI_EQ_PAGE_UPPER, i,
>>> +				    upper_32_bits(addr));
>>> +	}
>>> +
>>> +	/* program memory region for MSI posted writes */
>>> +	for (i = 0; i < msi->n_msi_msg_region; i++) {
>>> +		phys_addr_t addr =
>>> +			virt_to_phys(msi->msi_base +
>>> +				     (i * MSI_MSG_MEM_REGION_SIZE));
>>
>> You seem to be a victim of checkpatch. Please don't split statements
>> like this, it just make it harder to read. My terminal can wrap lines
>> very conveniently, and I don't care about the 80 character limit...
>>
> 
> Okay will fix.
> 
>>> +
>>> +		iproc_msi_write_reg(msi, IPROC_MSI_PAGE, i,
>>> +				    lower_32_bits(addr));
>>> +		iproc_msi_write_reg(msi, IPROC_MSI_PAGE_UPPER, i,
>>> +				    upper_32_bits(addr));
>>> +	}
>>> +
>>> +	for (eq = 0; eq < msi->nirqs; eq++) {
>>> +		/* enable MSI event queue */
>>> +		val = IPROC_MSI_INTR_EN | IPROC_MSI_INT_N_EVENT |
>>> +			IPROC_MSI_EQ_EN;
>>> +		iproc_msi_write_reg(msi, IPROC_MSI_CTRL, eq, val);
>>> +
>>> +		/*
>>> +		 * Some legacy platforms require the MSI interrupt enable
>>> +		 * register to be set explicitly
>>> +		 */
>>> +		if (msi->has_inten_reg) {
>>> +			val = readl(pcie->base + IPROC_MSI_INTS_EN_OFFSET);
>>> +			val |= BIT(eq);
>>> +			writel(val, pcie->base + IPROC_MSI_INTS_EN_OFFSET);
>>> +		}
>>> +	}
>>> +}
>>> +
>>> +static void iproc_msi_handler(struct irq_desc *desc)
>>> +{
>>> +	unsigned int irq = irq_desc_get_irq(desc);
>>> +	struct irq_chip *irq_chip = irq_desc_get_chip(desc);
>>> +	struct iproc_msi *msi;
>>> +	struct iproc_pcie *pcie;
>>> +	u32 eq, head, tail, num_events;
>>> +	int virq;
>>> +
>>> +	chained_irq_enter(irq_chip, desc);
>>> +
>>> +	msi = irq_get_handler_data(irq);
>>> +	pcie = msi->pcie;
>>> +
>>> +	eq = irq - msi->irqs[0];
>>> +	virq = irq_find_mapping(msi->inner_domain, eq);
>>> +	head = iproc_msi_read_reg(msi, IPROC_MSI_EQ_HEAD, eq) &
>>> +		IPROC_MSI_EQ_MASK;
>>> +	do {
>>> +		tail = iproc_msi_read_reg(msi, IPROC_MSI_EQ_TAIL, eq) &
>>> +			IPROC_MSI_EQ_MASK;
>>> +
>>> +		num_events = (tail < head) ?
>>> +			(IPROC_MSI_EQ_LEN - (head - tail)) : (tail - head);
>>> +		if (!num_events)
>>> +			break;
>>> +
>>> +		generic_handle_irq(virq);
>>> +
>>> +		head++;
>>> +		head %= IPROC_MSI_EQ_LEN;
>>> +		iproc_msi_write_reg(msi, IPROC_MSI_EQ_HEAD, eq, head);
>>> +	} while (true);
>>
>> That's unusual. You seem to get only one interrupt for a bunch of MSIs,
>> all representing the same IRQ? That feels very weird, as you can
>> usually collapse edge interrupts.
>>
> 
> I think we get one GIC interrupt per MSI line (1:1 mapping), but then 
> the MSI data message can be more than one, stored in the event queue 
> reserved for that MSI/interrupt line.

But can you have different messages? Buffering the same message N times
is pretty useless (you can coalesce MSIs), but I'd completely understand
the design if you could store N different messages. If that's the case,
then the HW design would actually be a lot saner (whoever thought that 4
or 6 MSIs would be enough needs a PCIe crash course...).

> When you mentioned chained IRQ above, do you really mean the logic here? 
> In fact, I don't think I really need to use the chained irq APIs here, 
> as the MSI and GIC interrupt line has a 1-to-1 mapping.

If you definitely have a 1:1 mapping, and that you cannot store
arbitrary messages in memory, then yes, you can switch to a fully
stacked configuration.

>>> +
>>> +	chained_irq_exit(irq_chip, desc);
>>> +}
>>> +
> 
> Can probably get rid of the chained_irq_enter and exit?

You could get rid of a lot more than that, but that depends on the above
discussion.

Thanks,

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