From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754273AbcAOPOf (ORCPT ); Fri, 15 Jan 2016 10:14:35 -0500 Received: from foss.arm.com ([217.140.101.70]:53555 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752542AbcAOPOd (ORCPT ); Fri, 15 Jan 2016 10:14:33 -0500 Message-ID: <56990CD4.6020405@arm.com> Date: Fri, 15 Jan 2016 15:14:28 +0000 From: Marc Zyngier Organization: ARM Ltd User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Icedove/31.7.0 MIME-Version: 1.0 To: Mark Rutland , Sinan Kaya CC: dmaengine@vger.kernel.org, timur@codeaurora.org, devicetree@vger.kernel.org, cov@codeaurora.org, vinod.koul@intel.com, jcm@redhat.com, agross@codeaurora.org, arnd@arndb.de, linux-arm-msm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, kvmarm@lists.cs.columbia.edu, christoffer.dall@linaro.org Subject: Re: [PATCH V12 3/7] dma: add Qualcomm Technologies HIDMA management driver References: <1452523550-8920-1-git-send-email-okaya@codeaurora.org> <1452523550-8920-4-git-send-email-okaya@codeaurora.org> <20160115145629.GI3262@leverpostej> In-Reply-To: <20160115145629.GI3262@leverpostej> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 15/01/16 14:56, Mark Rutland wrote: > Hi, > > [adding KVM people, given this is meant for virtualization] > > On Mon, Jan 11, 2016 at 09:45:43AM -0500, Sinan Kaya wrote: >> The Qualcomm Technologies HIDMA device has been designed to support >> virtualization technology. The driver has been divided into two to follow >> the hardware design. >> >> 1. HIDMA Management driver >> 2. HIDMA Channel driver >> >> Each HIDMA HW consists of multiple channels. These channels share some set >> of common parameters. These parameters are initialized by the management >> driver during power up. Same management driver is used for monitoring the >> execution of the channels. Management driver can change the performance >> behavior dynamically such as bandwidth allocation and prioritization. >> >> The management driver is executed in hypervisor context and is the main >> management entity for all channels provided by the device. > > You mention repeatedly that this is designed for virtualization, but > looking at the series as it stands today I can't see how this operates > from the host side. Nor the guest's, TBH. How do host and guest communicate, what is the infrastructure, how is it meant to be used? A lot of questions, and no answer whatsoever in this series. > > This doesn't seem to tie into KVM or VFIO, and as far as I can tell > there's no mechanism for associating channels with a particular virtual > address space (i.e. no configuration of an external or internal IOMMU), > nor pinning of guest pages to allow for DMA to occur safely. > > Given that, I'm at a loss as to how this would be used in a hypervisor > context. What am I missing? > > Are there additional patches, or do you have some userspace that works > with this in some limited configuration? Well, this looks so far like a code dumping exercise. I'd very much appreciate a HIDMA101 crash course: - How do host and guest communicate? - How is the integration performed in the hypervisor? - Does the HYP side requires any context switch (and how is that done)? - What makes it safe? Without any of this information (and pointer to the code to back it up), I'm very reluctant to take any of this. Thanks, M. -- Jazz is not dead. It just smells funny...