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From: Ard Biesheuvel <ardb@kernel.org>
To: Alan Mikhak <alan.mikhak@sifive.com>
Cc: Joao Pinto <Joao.Pinto@synopsys.com>,
	Bjorn Helgaas <bhelgaas@google.com>,
	Graeme Gregory <graeme.gregory@linaro.org>,
	Jingoo Han <jingoohan1@gmail.com>,
	linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
	linux-pci <linux-pci@vger.kernel.org>,
	Leif Lindholm <leif@nuviainc.com>, Marc Zyngier <maz@kernel.org>
Subject: Re: [PATCH 2/3] pci: designware: add separate driver for the MSI part of the RC
Date: Sat, 15 Feb 2020 10:35:56 +0100
Message-ID: <CAKv+Gu9W0v9owp85hkAatwCvu-y9z4BZxvbKf92N-s_nnD910Q@mail.gmail.com> (raw)
In-Reply-To: <1581728065-5862-1-git-send-email-alan.mikhak@sifive.com>

(updated some email addresses in cc, including my own)

On Sat, 15 Feb 2020 at 01:54, Alan Mikhak <alan.mikhak@sifive.com> wrote:
>
> Hi..
>
> What is the right approach for adding MSI support for the generic
> Linux PCI host driver?
>
> I came across this patch which seems to address a similar
> situation. It seems to have been dropped in v3 of the patchset
> with the explanation "drop MSI patch [for now], since it
> turns out we may not need it".
>
> [PATCH 2/3] pci: designware: add separate driver for the MSI part of the RC
> https://lore.kernel.org/linux-pci/20170821192907.8695-3-ard.biesheuvel@linaro.org/
>
> [PATCH v2 2/3] pci: designware: add separate driver for the MSI part of the RC
> https://lore.kernel.org/linux-pci/20170824184321.19432-3-ard.biesheuvel@linaro.org/
>
> [PATCH v3 0/2] pci: add support for firmware initialized designware RCs
> https://lore.kernel.org/linux-pci/20170828180437.2646-1-ard.biesheuvel@linaro.org/
>

For the platform in question, it turned out that we could use the MSI
block of the core's GIC interrupt controller directly, which is a much
better solution.

In general, turning MSIs into wired interrupts is not a great idea,
since the whole point of MSIs is that they are sufficiently similar to
other DMA transactions to ensure that the interrupt won't arrive
before the related memory transactions have completed.

If your interrupt controller does not have this capability, then yes,
you are stuck with this little widget that decodes an inbound write to
a magic address and turns it into a wired interrupt.

I'll leave it up to the Synopsys folks to comment on whether this
feature is generic enough to describe it like this, but if so, I think
it still makes sense to model it this way rather than fold it into the
RC driver and description.

  reply index

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-08-21 19:29 [PATCH 0/3] pci: add support for firmware initialized designware RCs Ard Biesheuvel
2017-08-21 19:29 ` [PATCH 2/3] pci: designware: add separate driver for the MSI part of the RC Ard Biesheuvel
2017-08-24 16:42   ` Bjorn Helgaas
2017-08-24 16:43     ` Ard Biesheuvel
2017-08-24 16:48   ` Robin Murphy
2017-08-24 16:50     ` Ard Biesheuvel
2020-02-15  0:54   ` Alan Mikhak
2020-02-15  9:35     ` Ard Biesheuvel [this message]
2020-02-15 10:36       ` Marc Zyngier
2020-02-18 19:09         ` Alan Mikhak
2020-02-19  8:11           ` Marc Zyngier
2020-02-19  8:17             ` Ard Biesheuvel
2020-02-19 20:24               ` Alan Mikhak
2020-02-19 21:06                 ` Ard Biesheuvel
2020-02-19 21:35                   ` Alan Mikhak
2017-08-21 19:29 ` [PATCH 3/3] dt-bindings: designware: add binding for Designware PCIe in ECAM mode Ard Biesheuvel
2017-08-24 16:46 ` [PATCH 0/3] pci: add support for firmware initialized designware RCs Bjorn Helgaas
2017-08-31 19:21   ` Ard Biesheuvel
2017-08-21 19:29 [PATCH 1/3] pci: designware: add driver for DWC controller in ECAM shift mode Ard Biesheuvel
2017-08-24 16:24 ` kbuild test robot
2017-08-24 16:25 ` kbuild test robot

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