From: helgaas@kernel.org (Bjorn Helgaas)
To: linux-arm-kernel@lists.infradead.org
Subject: Why does BIOS assign memory to 16 byte BAR
Date: Fri, 22 Jul 2016 10:51:33 -0500 [thread overview]
Message-ID: <20160722155133.GB20646@localhost> (raw)
In-Reply-To: <20160722151546.GA20646@localhost>
On Fri, Jul 22, 2016 at 10:15:46AM -0500, Bjorn Helgaas wrote:
> Hi Bharat,
>
> On Fri, Jul 22, 2016 at 09:24:22AM +0000, Bharat Kumar Gogada wrote:
> > Hi,
> >
> > I'm observing that on x86 BIOS successfully assigns memory if an End point requests
> > BAR of size 16byte.
> >
> > But as per Spec:
> > The minimum memory address range requested by a BAR is 128 bytes.
>
> Can you provide the spec reference for this? I don't see it in PCI
> r3.0.
>
> PCI r3.0, sec 6.2.5.1, shows bits 4-31 of a memory BAR as writable,
> which would correspond to a minimum size of 16 bytes.
The reference above is to the conventional PCI spec. I happened to
trip over a note in PCIe r3.0, sec 1.3.2.2, that for a PCI Express
endpoint, "the minimum memory address range requested by a BAR is 128
bytes."
I don't think linux currently enforces this minimum.
Bjorn
next prev parent reply other threads:[~2016-07-22 15:51 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-07-22 9:24 Why does BIOS assign memory to 16 byte BAR Bharat Kumar Gogada
2016-07-22 15:15 ` Bjorn Helgaas
2016-07-22 15:51 ` Bjorn Helgaas [this message]
2016-07-22 16:39 ` Bharat Kumar Gogada
2016-07-25 5:23 ` Bharat Kumar Gogada
2016-07-26 15:24 ` Bharat Kumar Gogada
2016-07-26 15:43 ` Bharat Kumar Gogada
2016-07-26 19:25 ` Yinghai Lu
2016-07-27 6:33 ` Bharat Kumar Gogada
2016-07-27 9:34 ` Lorenzo Pieralisi
2016-07-27 10:09 ` Bharat Kumar Gogada
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