linux-kernel - Re: [PATCH] PCI: dwc: Use level-triggered handler for MSI IRQs

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Message-ID: <20241230171145.hsqynixmowjn77ki@thinkpad>
Date: Mon, 30 Dec 2024 22:41:45 +0530
From: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To: Brian Norris <briannorris@...omium.org>
Cc: Jingoo Han <jingoohan1@...il.com>,
	Lorenzo Pieralisi <lpieralisi@...nel.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>, linux-kernel@...r.kernel.org,
	linux-pci@...r.kernel.org, Rob Herring <robh@...nel.org>,
	Marc Zyngier <marc.zyngier@....com>,
	Krzysztof Wilczyński <kw@...ux.com>,
	Brian Norris <briannorris@...gle.com>
Subject: Re: [PATCH] PCI: dwc: Use level-triggered handler for MSI IRQs

On Tue, Oct 15, 2024 at 02:12:16PM -0700, Brian Norris wrote:
> From: Brian Norris <briannorris@...gle.com>
> 
> Per Synopsis's documentation, the msi_ctrl_int signal is
> level-triggered, not edge-triggered.
> 

Could you please quote the spec reference?

- Mani

> The use of handle_edge_trigger() was chosen in commit 7c5925afbc58
> ("PCI: dwc: Move MSI IRQs allocation to IRQ domains hierarchical API"),
> which actually dropped preexisting use of handle_level_trigger().
> Looking at the patch history, this change was only made by request:
> 
>   Subject: Re: [PATCH v6 1/9] PCI: dwc: Add IRQ chained API support
>   https://lore.kernel.org/all/04d3d5b6-9199-218d-476f-c77d04b8d2e7@arm.com/
> 
>   "Are you sure about this "handle_level_irq"? MSIs are definitely edge
>    triggered, not level."
> 
> However, while the underlying MSI protocol is edge-triggered in a sense,
> the DesignWare IP is actually level-triggered.
> 
> So, let's switch back to level-triggered.
> 
> In many cases, the distinction doesn't really matter here, because this
> signal is hidden behind another (chained) top-level IRQ which can be
> masked on its own. But it's still wise to manipulate this interrupt line
> according to its actual specification -- specifically, to mask it while
> we handle it.
> 
> Signed-off-by: Brian Norris <briannorris@...gle.com>
> Signed-off-by: Brian Norris <briannorris@...omium.org>
> ---
> 
>  drivers/pci/controller/dwc/pcie-designware-host.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c b/drivers/pci/controller/dwc/pcie-designware-host.c
> index 3e41865c7290..0fb79a26d05e 100644
> --- a/drivers/pci/controller/dwc/pcie-designware-host.c
> +++ b/drivers/pci/controller/dwc/pcie-designware-host.c
> @@ -198,7 +198,7 @@ static int dw_pcie_irq_domain_alloc(struct irq_domain *domain,
>  	for (i = 0; i < nr_irqs; i++)
>  		irq_domain_set_info(domain, virq + i, bit + i,
>  				    pp->msi_irq_chip,
> -				    pp, handle_edge_irq,
> +				    pp, handle_level_irq,
>  				    NULL, NULL);
>  
>  	return 0;
> -- 
> 2.47.0.rc1.288.g06298d1525-goog
> 

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