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Re: [PATCH V14 0/9] dma: add Qualcomm Technologies HIDMA driver

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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

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[PATCH V14 0/9] dma: add Qualcomm Technologies HIDMA driver Sinan Kaya <okaya@codeaurora.org> - 2016-02-05 05:40 +0100
  [PATCH V14 1/9] dma: qcom_bam_dma: move to qcom directory Sinan Kaya <okaya@codeaurora.org> - 2016-02-05 05:40 +0100
  [PATCH V14 5/9] dma: qcom_hidma: implement lower level hardware interface Sinan Kaya <okaya@codeaurora.org> - 2016-02-05 05:40 +0100
  [PATCH V14 2/9] dma: hidma: Add Device Tree binding Sinan Kaya <okaya@codeaurora.org> - 2016-02-05 05:40 +0100
  [PATCH V14 6/9] dma: qcom_hidma: add debugfs hooks Sinan Kaya <okaya@codeaurora.org> - 2016-02-05 05:40 +0100
  [PATCH V14 7/9] dma: qcom_hidma: add support for object hierarchy Sinan Kaya <okaya@codeaurora.org> - 2016-02-05 05:40 +0100
  [PATCH V14 9/9] vfio, platform: add QTI HIDMA reset driver Sinan Kaya <okaya@codeaurora.org> - 2016-02-05 05:40 +0100
  [PATCH V14 8/9] vfio, platform: add support for ACPI while detecting the reset driver Sinan Kaya <okaya@codeaurora.org> - 2016-02-05 05:40 +0100
  [PATCH V14 3/9] dma: add Qualcomm Technologies HIDMA management driver Sinan Kaya <okaya@codeaurora.org> - 2016-02-05 05:40 +0100
  [PATCH V14 4/9] dma: add Qualcomm Technologies HIDMA channel driver Sinan Kaya <okaya@codeaurora.org> - 2016-02-05 05:40 +0100
  Re: [PATCH V14 0/9] dma: add Qualcomm Technologies HIDMA driver Christoffer Dall <christoffer.dall@linaro.org> - 2016-02-08 11:20 +0100
    Re: [PATCH V14 0/9] dma: add Qualcomm Technologies HIDMA driver Sinan Kaya <okaya@codeaurora.org> - 2016-02-08 15:30 +0100
      Re: [PATCH V14 0/9] dma: add Qualcomm Technologies HIDMA driver Christoffer Dall <christoffer.dall@linaro.org> - 2016-02-08 18:10 +0100

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