netdev - Re: Legacy features in PCI Express devices

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Date:   Mon, 13 Mar 2017 04:08:03 -0700
From:   Greg <gvrose8192@...il.com>
To:     Mason <slash.tmp@...e.fr>
Cc:     linux-pci <linux-pci@...r.kernel.org>,
        Bjorn Helgaas <helgaas@...nel.org>,
        David Laight <david.laight@...lab.com>,
        Robin Murphy <robin.murphy@....com>,
        Thibaud Cornic <thibaud_cornic@...madesigns.com>,
        Phuong Nguyen <phuong_nguyen@...madesigns.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        netdev <netdev@...r.kernel.org>,
        Tim Harvey <tharvey@...eworks.com>,
        Arnd Bergmann <arnd@...db.de>
Subject: Re: Legacy features in PCI Express devices

On Mon, 2017-03-13 at 17:10 +0100, Mason wrote:
> Hello,
> 
> There are two revisions of our PCI Express controller.
> 
> Rev 1 did not support the following features:
> 
>   1) legacy PCI interrupt delivery (INTx signals)

I'm not sure about this...

>   2) I/O address space

But yes, definitely some support this.

We're working on a new type of network controller that uses I/O for some
types of low latency feature support.

- Greg

> 
> Internally, someone stated that such missing support would prevent
> some PCIe cards from working with our controller.
> 
> Are there really modern PCIe cards that require 1) and/or 2)
> to function?
> 
> Can someone provide examples of such cards, so that I may test them
> on both revisions?
> 
> I was told to check ath9k-based cards. Any other examples?
> 
> Looking around, I came across this thread:
> http://lists.infradead.org/pipermail/linux-arm-kernel/2016-March/418254.html
> "i.MX6 PCIe: Fix imx6_pcie_deassert_core_reset() polarity"
> 
> IIUC, although some PCIe boards do support MSI, the driver might not
> put in the work to use that infrastructure, and instead reverts to
> legacy interrupts. (So it is a SW issue, in a sense.)
> 
> Regards.