linux-kernel - Re: [PATCH V6 XDMA 0/2] xilinx XDMA driver

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Date:   Fri, 7 Oct 2022 15:21:09 +0200
From:   Martin Tůma <tumic@...see.org>
To:     Lizhi Hou <lizhi.hou@....com>, vkoul@...nel.org,
        dmaengine@...r.kernel.org, linux-kernel@...r.kernel.org,
        trix@...hat.com
Cc:     max.zhen@....com, sonal.santan@....com, larry.liu@....com,
        brian.xu@....com
Subject: Re: [PATCH V6 XDMA 0/2] xilinx XDMA driver

On 06. 10. 22 19:42, Lizhi Hou wrote:
> 
> On 10/6/22 09:37, Martin Tůma wrote:
>> On 04. 10. 22 23:43, Lizhi Hou wrote:
>>> Hello,
>>>
>>> This V6 of patch series is to provide the platform driver to support the
>>> Xilinx XDMA subsystem. The XDMA subsystem is used in conjunction with 
>>> the
>>> PCI Express IP block to provide high performance data transfer 
>>> between host
>>> memory and the card's DMA subsystem. It also provides up to 16 user
>>> interrupt wires to user logic that generate interrupts to the host.
>>>
>>>              +-------+       +-------+       +-----------+
>>>     PCIe     |       |       |       |       |           |
>>>     Tx/Rx    |       |       |       |  AXI  |           |
>>>   <=======>  | PCIE  | <===> | XDMA  | <====>| User Logic|
>>>              |       |       |       |       |           |
>>>              +-------+       +-------+       +-----------+
>>>
>>> The XDMA has been used for Xilinx Alveo PCIe devices.
>>> And it is also integrated into Versal ACAP DMA and Bridge Subsystem.
>>>      https://www.xilinx.com/products/boards-and-kits/alveo.html
>>> https://docs.xilinx.com/r/en-US/pg344-pcie-dma-versal/Introduction-to-the-DMA-and-Bridge-Subsystems
>>>
>>> The device driver for any FPGA based PCIe device which leverages XDMA 
>>> can
>>> call the standard dmaengine APIs to discover and use the XDMA subsystem
>>> without duplicating the XDMA driver code in its own driver.
>>>
>>> Changes since v5:
>>> - Modified user logic interrupt APIs to handle user logic IP which 
>>> does not
>>>    have its own register to enable/disable interrupt.
>>> - Clean up code based on review comments.
>>>
>>> Changes since v4:
>>> - Modified user logic interrupt APIs.
>>>
>>> Changes since v3:
>>> - Added one patch to support user logic interrupt.
>>>
>>> Changes since v2:
>>> - Removed tasklet.
>>> - Fixed regression bug introduced to V2.
>>> - Test Robot warning.
>>>
>>> Changes since v1:
>>> - Moved filling hardware descriptor to xdma_prep_device_sg().
>>> - Changed hardware descriptor enum to "struct xdma_hw_desc".
>>> - Minor changes from code review comments.
>>>
>>> Lizhi Hou (2):
>>>    dmaengine: xilinx: xdma: Add xilinx xdma driver
>>>    dmaengine: xilinx: xdma: Add user logic interrupt support
>>>
>>>   MAINTAINERS                            |   11 +
>>>   drivers/dma/Kconfig                    |   13 +
>>>   drivers/dma/xilinx/Makefile            |    1 +
>>>   drivers/dma/xilinx/xdma-regs.h         |  171 ++++
>>>   drivers/dma/xilinx/xdma.c              | 1034 ++++++++++++++++++++++++
>>>   include/linux/dma/amd_xdma.h           |   16 +
>>>   include/linux/platform_data/amd_xdma.h |   34 +
>>>   7 files changed, 1280 insertions(+)
>>>   create mode 100644 drivers/dma/xilinx/xdma-regs.h
>>>   create mode 100644 drivers/dma/xilinx/xdma.c
>>>   create mode 100644 include/linux/dma/amd_xdma.h
>>>   create mode 100644 include/linux/platform_data/amd_xdma.h
>>>
>>
>> Hi,
>> I have rewritten our V4L2 driver to use this new XDMA driver, but it 
>> does not work on our HW (where the previous Xilinx XDMA driver derived 
>> from the Xilinx sample code worked fine). The driver is sucessfully 
>> loaded and 4(2+2) DMA channels are successfully created. But when a 
>> DMA transfer is initiated, I get an error from my PC's DMA chip:
>>
>> AMD-Vi: Event logged [IO_PAGE_FAULT domain=0x000a address=0x36a00000 
>> flags=0x0000]
>>
>> and no error from XDMA.
>>
>> Does the driver expect some special FPGA IP core configuration? Or is 
>> there something else I'm missing? My code is quiet similar to what you 
>> use in your XRT repo on GitHub (there is btw. a bug in the XRT code - 
>> you do not clear the dma_slave_config struct before using) but in my 
>> case the DMA transfer triggers the AMD-Vi error and timeouts.
>>
>> The code of our driver is attached, the relevant parts are in mgb4_dma.c
>> and mgb4_core.c.
>>
>> M.
> 
> Hi Martin,
> 
> Thanks for trying this and got a lot thing works. I have read your 
> driver. Could you call pci_map_sg() before calling prep_sg()? (and 
> pci_unmap_sg()) after transfer complete?
> 
> example: 
> https://github.com/houlz0507/XRT-1/blob/xdma_v4_usage/src/runtime_src/core/pcie/driver/linux/xocl/subdev/xdma.c#L103
> 
> 
> Thanks,
> 
> Lizhi
> 

Hi,
That's not the problem, the sg is already mapped by V4L2 videobuf-dma-sg
(https://elixir.bootlin.com/linux/v6.0/source/drivers/media/v4l2-core/videobuf-dma-sg.c#L285). 
With the original XDMA driver I was also not mapping the sg and it 
worked fine. And yes, I have tried it anyway and it didn't help ;-)

So there must be some other problem in your XDMA driver.

M.