On Mon, Feb 08, 2016 at 09:24:39AM -0500, Sinan Kaya wrote: > Hi, > > On 2/8/2016 5:14 AM, Christoffer Dall wrote: > > Hi Sinan, > > > > On Thu, Feb 04, 2016 at 11:34:31PM -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 in the future. > >> > >> The management driver is executed in host context and > >> is the main management entity for all channels provided by > >> the device. > > > > I'm not at all familiar with this kind of hardware. > > > > Let me help. > > > Once an entity (userspace or VM) has a HIDAM channel assigned via VFIO, > > how does it use it? > > HIDMA is a HW accelerator for memory operations like memcpy and memset. It fits > into the DMA engine framework. > > There are two classes of DMA HW. These are slave DMA and standalone DMA. Slave DMA > is generally related to another piece of HW that needs DMA for moving data. > Standalone DMA is intended for OS/CPU consumption not HW. These can be used to offload > crypto operations (XOR) or other memory transactions (memcpy and memset) that are > lengthy. > > Once the HIDMA channel is assigned to the guest machine, guest operating system uses the > DMA channel to offload memory operations as HIDMA only supports memcpy. > > IOMMU HW provides the isolation from the rest of the host kernel or from other guest machines. > > > Is it used in relation with another device to > > perform DMA on its behalf or is a HIDMA channel something that's useful > > on its own? > > It is standalone only. The relationship you are referring to is known as slave DMA engine. > HIDMA does not support slave DMA. HIDMA only supports memcpy and memset in HW and only memcpy in SW > as the memset support has been removed from the kernel long time ago. > Thanks for the explanation. -Christoffer -- To unsubscribe from this list: send the line "unsubscribe linux-arm-msm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
