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From: Bjorn Helgaas <helgaas@kernel.org>
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
	linux-pci <linux-pci@vger.kernel.org>,
	Sinan Kaya <okaya@kernel.org>,
	linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
	Ard Biesheuvel <ard.biesheuvel@linaro.org>
Subject: Re: [RFC PATCH v2] arm64: acpi/pci: invoke _DSM whether to preserve firmware PCI setup
Date: Fri, 14 Jun 2019 15:13:18 -0500
Message-ID: <20190614201318.GT13533@google.com> (raw)
In-Reply-To: <fdedfe23250f0dcb49619ed9da1d53ff7e7403d8.camel@kernel.crashing.org>

On Fri, Jun 14, 2019 at 11:48:18PM +1000, Benjamin Herrenschmidt wrote:
> On Fri, 2019-06-14 at 08:12 -0500, Bjorn Helgaas wrote:
> > On Fri, Jun 14, 2019 at 08:43:19PM +1000, Benjamin Herrenschmidt
> > wrote:
> > 
> > > This least to another conversation we hinted at earlier.. we should
> > > probably have a way to do the same at least for BARs on ACPI
> > > systems so
> > > we don't have to temporarily disable access to a device to size
> > > them.
> > 
> > The PCI Enhanced Allocation capability provides a way to do this.  I
> > don't know how widely used it is, but it's theoretically possible.
> 
> Ok, I have to read about this. I haven't seen a device with that on
> yet, it looks messy at a quick glance.
> 
> Can ACPI convey the information ? On powerpc and sparc64 we have ways
> to read the BAR values from the device-tree created by OF when it
> assigned them.

I agree, EA is messy.

I don't think it's feasible to do this in ACPI.  It's a pretty
fundamental principle of PCI that you can discover what resources a
device needs and uses by looking at its config space.  In general PCIe
requires ECAM, which gives the OS direct access to config space,
although it does allow exceptions for architecture-specific firmware
interfaces for accessing config space, e.g., ia64 SAL (PCIe r4.0, sec
7.2.2).

Bjorn

  reply index

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-06-13  7:54 Benjamin Herrenschmidt
2019-06-13 19:02 ` Bjorn Helgaas
2019-06-13 21:59   ` Benjamin Herrenschmidt
2019-06-13 23:07   ` Benjamin Herrenschmidt
2019-06-14  7:42     ` Ard Biesheuvel
2019-06-14  8:36       ` Benjamin Herrenschmidt
2019-06-14  9:57         ` Lorenzo Pieralisi
2019-06-14 10:36           ` Benjamin Herrenschmidt
2019-06-14 10:43             ` Benjamin Herrenschmidt
2019-06-14 13:12               ` Bjorn Helgaas
2019-06-14 13:48                 ` Benjamin Herrenschmidt
2019-06-14 20:13                   ` Bjorn Helgaas [this message]
2019-06-15  1:18                     ` Benjamin Herrenschmidt
2019-06-14 13:09         ` Bjorn Helgaas
2019-06-14 13:46           ` Benjamin Herrenschmidt

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