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From: Brijesh Singh <brijesh.singh@amd.com>
To: edk2-devel@lists.01.org
Cc: Brijesh Singh <brijesh.singh@amd.com>,
	Ard Biesheuvel <ard.biesheuvel@linaro.org>,
	Jordan Justen <jordan.l.justen@intel.com>,
	Tom Lendacky <thomas.lendacky@amd.com>,
	Laszlo Ersek <lersek@redhat.com>
Subject: [PATCH v4 5/8] OvmfPkg/VirtioNetDxe: update TechNotes
Date: Thu, 14 Sep 2017 16:22:44 -0500	[thread overview]
Message-ID: <20170914212247.124937-6-brijesh.singh@amd.com> (raw)
In-Reply-To: <20170914212247.124937-1-brijesh.singh@amd.com>

In next patches we will update Virtio transmit to use the device-mapped
address of the caller-supplied packet. The patch documents the new model.

Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
---
 OvmfPkg/VirtioNetDxe/TechNotes.txt | 20 +++++++++++++-------
 1 file changed, 13 insertions(+), 7 deletions(-)

diff --git a/OvmfPkg/VirtioNetDxe/TechNotes.txt b/OvmfPkg/VirtioNetDxe/TechNotes.txt
index fedbaee07ec7..40a22f66dc22 100644
--- a/OvmfPkg/VirtioNetDxe/TechNotes.txt
+++ b/OvmfPkg/VirtioNetDxe/TechNotes.txt
@@ -312,10 +312,14 @@ in the following:
   that is shared by all of the head descriptors. This virtio-net request header
   is never modified by the host.
 
-- Each tail descriptor is re-pointed to the caller-supplied packet buffer
-  whenever VirtioNetTransmit places the corresponding head descriptor on the
-  Available Ring. The caller is responsible to hang on to the unmodified buffer
-  until it is reported transmitted by VirtioNetGetStatus.
+- Each tail descriptor is re-pointed to the device-mapped address of the
+  caller-supplied packet buffer whenever VirtioNetTransmit places the
+  corresponding head descriptor on the Available Ring. A reverse mapping, from
+  the device-mapped address to the caller-supplied packet address, is saved in
+  an associative data structure that belongs to the driver instance.
+
+- Per spec, the caller is responsible to hang on to the unmodified packet
+  buffer until it is reported transmitted by VirtioNetGetStatus.
 
 Steps of packet transmission:
 
@@ -338,9 +342,11 @@ Steps of packet transmission:
 - Client code calls VirtioNetGetStatus. In case the Used Ring is empty, the
   function reports no Tx completion. Otherwise, a head descriptor's index is
   consumed from the Used Ring and recycled to the private stack. The client
-  code's original packet buffer address is fetched from the tail descriptor
-  (where it has been stored at VirtioNetTransmit time) and returned to the
-  caller.
+  code's original packet buffer address is calculated by fetching the
+  device-mapped address from the tail descriptor (where it has been stored at
+  VirtioNetTransmit time), and by looking up the device-mapped address in the
+  associative data structure. The reverse-mapped packet buffer address is
+  returned to the caller.
 
 - The Len field of the Used Ring Element is not checked. The host is assumed to
   have transmitted the entire packet -- VirtioNetTransmit had forced it below
-- 
2.9.5



  parent reply	other threads:[~2017-09-14 21:20 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-09-14 21:22 [PATCH v4 0/8] OvmfPkg/VirtioNetDxe: map host address to device address Brijesh Singh
2017-09-14 21:22 ` [PATCH v4 1/8] OvmfPkg/VirtioNetDxe: add helper VirtioNetUninitRing() Brijesh Singh
2017-09-14 21:22 ` [PATCH v4 2/8] OvmfPkg/VirtioNetDxe: map VRINGs using VirtioRingMap() Brijesh Singh
2017-09-14 21:22 ` [PATCH v4 3/8] OvmfPkg/VirtioNetDxe: alloc RxBuf using AllocateSharedPages() Brijesh Singh
2017-09-14 21:22 ` [PATCH v4 4/8] OvmfPkg/VirtioNetDxe: dynamically alloc transmit header Brijesh Singh
2017-09-14 21:22 ` Brijesh Singh [this message]
2017-09-14 21:22 ` [PATCH v4 6/8] OvmfPkg/VirtioNetDxe: add Tx packet map/unmap helper functions Brijesh Singh
2017-09-14 21:22 ` [PATCH v4 7/8] OvmfPkg/VirtioNetDxe: map caller-supplied Tx packet to device-address Brijesh Singh
2017-09-14 21:49   ` Laszlo Ersek
2017-09-14 21:22 ` [PATCH v4 8/8] OvmfPkg/VirtioNetDxe: negotiate VIRTIO_F_IOMMU_PLATFORM Brijesh Singh
2017-09-15  0:10 ` [PATCH v4 0/8] OvmfPkg/VirtioNetDxe: map host address to device address Laszlo Ersek
2017-09-15  0:14   ` Laszlo Ersek

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