linux-xlnx kernel on the Parallella

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linux-xlnx kernel on the Parallella

Postby yanidubin » Thu Sep 18, 2014 10:18 am

I wanted to check whether anyone has already played with the linux-xlnx kernel on the Parallella. I believe it might give me a short route to proving ARM-FPGA AXI DMA transfers since there is a kernel driver, and a 3rd party driver has been written and reportedly works on the Zedboard.

So, has anyone attempted to get this kernel running on the Parallella?

I have no knowledge of the differences between Zedboard and Parallella (other than lack of Epiphany) - but I hope the proposed approach means I'm not going to toast anything through ignorant hacking. Can anyone who is knowledgeable about the differences between the Zedboard and the Parallella comment?

I have no interest in HDMI (is this the only reason Parallella are using the ADI kernel in particular and not mainline?), as I have only used my Parallella headless and have no HDMI cables to my name. I do not need access to the Epiphany - this is a temporary runup to experiment with AXI DMA. If the results are pleasing, and nobody suggests a better approach, I might then look to porting it to the parallella kernel.

I will be simply using my own bitstream based on the Parallella - so not using one from a zedboard or anything weird like that. I'll revert to a stock Ubuntu rootfs, as I know to run ArchLinux (my favored rootfs), some kernel config changes were required. I'd rather avoid any potential issues there for now.

I expect the process will look something like:
1) Build linux-xlnx kernel using zedboard_defconfig
2) Merge in the devicetree, as this has bindings for the driver in question (I'll only be pulling in AMBA/AXI related entries)
3) See how well it boots up
4) If the magic smoke favors my efforts, reconfigure, rinse, repeat until I get a Linux prompt.

This seems like a safe approach to me since I'm using pinmux/frequency/allmost-everything settings from the Parallella dts, and the bitstream from the Parallella. Yes, there'll be a whole bunch of different drivers configured (a diff between the kernel configs a few weeks back was not insignificant - partly due to difference in versions I expect), but I can't see that being much of an issue - just might be missing stuff I need. Like boot params (console on the right port, correct mmc interface, etc).

Any comments from the experts?
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Re: linux-xlnx kernel on the Parallella

Postby aolofsson » Thu Sep 18, 2014 12:10 pm

We are working on linux update now. The ADI and Xilinx Linux trees are not identical, but the new one we pulled from ADI has the functionality you need. It would be hard to break anything, unless you start messing around with I2C and changing the voltage rails to the on-board voltage regulator.

The latest Linux work is here.
https://github.com/parallella/parallella-linux

Andreas
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Re: linux-xlnx kernel on the Parallella

Postby yanidubin » Thu Sep 18, 2014 8:41 pm

Thanks Andreas - yes, I took a look at the source, and it does indeed have the kernel driver I am after (going by the devicetree bindings). I will give this ago over the weekend.
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Re: linux-xlnx kernel on the Parallella

Postby yanidubin » Thu Sep 18, 2014 8:55 pm

Actually, this driver (dma-axi-dmac) seems to have ben present in the 3.12 sources I have been working with (parallella-linux-adi, xcomm_zynq branch) also. Either not working, or I neglected to set CONFIG_DMA_AXI_DMAC, despite going over all the DMA related things a number of times (doesn't appear to be set locally just now).

But I will certainly give this another shot before resorting to building the linux-xlnx kernel.
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