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From: Bjorn Helgaas <helgaas@kernel.org>
To: Jeremy Linton <jeremy.linton@arm.com>
Cc: linux-pci@vger.kernel.org, lorenzo.pieralisi@arm.com,
	nsaenz@kernel.org, bhelgaas@google.com, rjw@rjwysocki.net,
	lenb@kernel.org, robh@kernel.org, kw@linux.com,
	f.fainelli@gmail.com, bcm-kernel-feedback-list@broadcom.com,
	linux-acpi@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
	linux-rpi-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/3] PCI: brcmstb: Add ACPI config space quirk
Date: Mon, 9 Aug 2021 15:33:23 -0500	[thread overview]
Message-ID: <20210809203323.GA2184624@bjorn-Precision-5520> (raw)
In-Reply-To: <4d4732b9-e8df-3803-2db7-c6eef1196269@arm.com>

On Mon, Aug 09, 2021 at 02:48:17PM -0500, Jeremy Linton wrote:
> Hi,
> 
> On 8/9/21 12:42 PM, Bjorn Helgaas wrote:
> > On Fri, Aug 06, 2021 at 09:55:27PM -0500, Jeremy Linton wrote:
> > > Hi,
> > > 
> > > On 8/6/21 5:21 PM, Bjorn Helgaas wrote:
> > > > On Thu, Aug 05, 2021 at 04:11:59PM -0500, Jeremy Linton wrote:
> > > > > The PFTF CM4 is an ACPI platform that is following the PCIe SMCCC
> > > > > standard because its PCIe config space isn't ECAM compliant and is
> > > > > split into two parts. One part for the root port registers and a
> > > > > moveable window which points at a given device's 4K config space.
> > > > > Thus it doesn't have a MCFG (and really any MCFG provided would be
> > > > > nonsense anyway). As Linux doesn't support the PCIe SMCCC standard
> > > > > we key off a Linux specific host bridge _DSD to add custom ECAM
> > > > > ops and cfgres. The cfg op selects between those two regions, as
> > > > > well as disallowing problematic accesses, particularly if the link
> > > > > is down because there isn't an attached device.
> > > > 
> > > > I'm not sure SMCCC is *really* relevant here.  If it is, an expansion
> > > > of the acronym and a link to a spec would be helpful.
> > > > 
> > > > But AFAICT the only important thing here is that it doesn't have
> > > > standard ECAM, and we're going to work around that.
> > > 
> > > I will reword it a bit.
> > > 
> > > > I don't see anything about _DSD in this series.
> > > 
> > > That is the "linux,pci-quirk" in the next patch.
> > 
> > The next patch doesn't mention _DSD either.  Is it obfuscated by
> > being inside fwnode_property_read_string()?  If so, it's well and
> > truly hidden; I gave up trying to connect that with ACPI.
> 
> Right, the fwnode stuff works as a DT/ACPI abstraction for reading values
> from firmware tables. In this case the ACPI definition looks something like:
> 
> Device(PCI0) {
> ...
>   Name (_DSD, Package () {
>   ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
>     Package () {
>     Package () { "linux-pcie-quirk", "bcm2711" },
>   }
>   })
> 
> ...
> }
> 
> Which explains a bit of why the underlying code is a bit uh... complicated.

Wow, that's ... special.

I think I would include "ecam" or something in the name.  There might
be a variety of quirks, e.g., "P2PDMA allowed between root ports",
that could reasonably fit under "linux-pcie-quirk".

  reply	other threads:[~2021-08-09 20:33 UTC|newest]

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-05 21:11 [PATCH 0/3] CM4 ACPI PCIe quirk Jeremy Linton
2021-08-05 21:11 ` [PATCH 1/3] PCI: brcmstb: Break register definitions into separate header Jeremy Linton
2021-08-10 10:07   ` Florian Fainelli
2021-08-10 15:10     ` Jeremy Linton
2021-08-11  8:39       ` Florian Fainelli
2021-08-05 21:11 ` [PATCH 2/3] PCI: brcmstb: Add ACPI config space quirk Jeremy Linton
2021-08-06 22:21   ` Bjorn Helgaas
2021-08-07  2:55     ` Jeremy Linton
2021-08-09 17:42       ` Bjorn Helgaas
2021-08-09 19:48         ` Jeremy Linton
2021-08-09 20:33           ` Bjorn Helgaas [this message]
2021-08-09 21:21             ` Jeremy Linton
2021-08-05 21:12 ` [PATCH 3/3] PCI/ACPI: Add new quirk detection, enable bcm2711 Jeremy Linton
2021-08-06 22:12   ` Bjorn Helgaas
2021-08-07  0:34     ` Jeremy Linton
2021-08-09 15:27       ` Rob Herring
2021-08-09 16:24         ` Jeremy Linton
2021-08-10 14:31   ` Shanker R Donthineni
2021-08-10 14:47     ` Jeremy Linton
2021-08-10 15:09       ` Shanker R Donthineni
2021-08-06 11:40 ` [PATCH 0/3] CM4 ACPI PCIe quirk Stefan Wahren

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