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

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Date:   Thu, 6 Oct 2022 10:42:44 -0700
From:   Lizhi Hou <lizhi.hou@....com>
To:     Martin Tůma <tumic@...see.org>,
        <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 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