Which DMA channel should I use to read from FPGA/memory (FMC)

[GLaure]

Hi,

I am puzzled which DMA channel to use to read from an FPGA connected to the FMC.

Using the dmatest module I found out which are free and can be used for DMA_MEMCPY

transfers:

modprobe dmatest timeout=2000 iterations=1  run=1 wait=1
[  991.821537] dmatest: No channels configured, continue with any
[  991.826830] dmatest: Added 1 threads using dma0chan19
[  991.831372] dmatest: Added 1 threads using dma0chan20
[  991.836463] dmatest: Added 1 threads using dma0chan21
[  991.841513] dmatest: Added 1 threads using dma0chan22
[  991.846879] dmatest: Added 1 threads using dma0chan23
[  991.851588] dmatest: Added 1 threads using dma0chan24
[  991.856713] dmatest: Added 1 threads using dma0chan25
[  991.861707] dmatest: Added 1 threads using dma0chan26
[  991.867050] dmatest: Added 1 threads using dma0chan27
[  991.871733] dmatest: Added 1 threads using dma0chan28
[  991.876972] dmatest: Added 1 threads using dma0chan29
[  991.881975] dmatest: Added 1 threads using dma0chan30
[  991.887247] dmatest: Added 1 threads using dma0chan31
[  991.892016] dmatest: Added 1 threads using dma1chan6
[  991.897143] dmatest: Added 1 threads using dma1chan7
[  991.902026] dmatest: Added 1 threads using dma2chan0
[  991.907331] dmatest: Added 1 threads using dma2chan1
[  991.911855] dmatest: Added 1 threads using dma2chan2
[  991.917077] dmatest: Added 1 threads using dma2chan3
[  991.921841] dmatest: Added 1 threads using dma2chan4
[  991.927076] dmatest: Added 1 threads using dma2chan5
[  991.931901] dmatest: Added 1 threads using dma2chan6
[  991.936889] dmatest: Added 1 threads using dma2chan7
[  991.941979] dmatest: Started 1 threads using dma0chan19
[  991.947127] dmatest: Started 1 threads using dma0chan20
[  991.948232] dmatest: dma0chan19-copy: summary 1 tests, 0 failures 178.92 iops 0 KB/s (0)
[  991.952384] dmatest: Started 1 threads using dma0chan21
[  991.960951] dmatest: dma0chan20-copy: summary 1 tests, 0 failures 77.91 iops 467 KB/s (0)
[  991.965846] dmatest: dma0chan21-copy: summary 1 tests, 0 failures 76.35 iops 534 KB/s (0)
[  991.976867] dmatest: Started 1 threads using dma0chan22
[  991.982391] dmatest: dma0chan22-copy: summary 1 tests, 0 failures 183.38 iops 733 KB/s (0)
[  991.987969] dmatest: Started 1 threads using dma0chan23
[  991.996468] dmatest: dma0chan23-copy: summary 1 tests, 0 failures 122.15 iops 1710 KB/s (0)
[  992.002495] dmatest: Started 1 threads using dma0chan24
[  992.009723] dmatest: dma0chan24-copy: summary 1 tests, 0 failures 144.21 iops 1009 KB/s (0)
[  992.015529] dmatest: Started 1 threads using dma0chan25
[  992.024914] dmatest: dma0chan25-copy: summary 1 tests, 0 failures 749.62 iops 4497 KB/s (0)
[  992.027981] dmatest: Started 1 threads using dma0chan26
[  992.039043] dmatest: dma0chan26-copy: summary 1 tests, 0 failures 1321.00 iops 13210 KB/s (0)
[  992.041868] dmatest: Started 1 threads using dma0chan27
[  992.051936] dmatest: dma0chan27-copy: summary 1 tests, 0 failures 102.65 iops 718 KB/s (0)
[  992.055825] dmatest: Started 1 threads using dma0chan28
[  992.065412] dmatest: dma0chan28-copy: summary 1 tests, 0 failures 107.79 iops 1509 KB/s (0)
[  992.068906] dmatest: Started 1 threads using dma0chan29
[  992.079423] dmatest: dma0chan29-copy: summary 1 tests, 0 failures 626.17 iops 8766 KB/s (0)
[  992.082366] dmatest: Started 1 threads using dma0chan30
[  992.093148] dmatest: dma0chan30-copy: summary 1 tests, 0 failures 626.56 iops 9398 KB/s (0)
[  992.096106] dmatest: Started 1 threads using dma0chan31
[  992.105372] dmatest: dma0chan31-copy: summary 1 tests, 0 failures 4255.31 iops 4255 KB/s (0)
[  992.109991] dmatest: Started 1 threads using dma1chan6
[  992.121032] dmatest: dma1chan6-copy0: summary 1 tests, 0 failures 93.46 iops 280 KB/s (0)
[  992.123645] dmatest: Started 1 threads using dma1chan7
[  992.133621] dmatest: dma1chan7-copy0: summary 1 tests, 0 failures 103.02 iops 1236 KB/s (0)
[  992.136708] dmatest: Started 1 threads using dma2chan0
[  992.147864] dmatest: dma2chan0-copy0: summary 1 tests, 0 failures 1250.00 iops 12500 KB/s (0)
[  992.150506] dmatest: Started 1 threads using dma2chan1
[  992.160822] dmatest: dma2chan1-copy0: summary 1 tests, 0 failures 100.26 iops 701 KB/s (0)
[  992.163851] dmatest: Started 1 threads using dma2chan2
[  992.175094] dmatest: dma2chan2-copy0: summary 1 tests, 0 failures 1236.09 iops 12360 KB/s (0)
[  992.177280] dmatest: Started 1 threads using dma2chan3
[  992.187974] dmatest: dma2chan3-copy0: summary 1 tests, 0 failures 4901.95 iops 0 KB/s (0)
[  992.191280] dmatest: Started 1 threads using dma2chan4
[  992.201263] dmatest: dma2chan4-copy0: summary 1 tests, 0 failures 103.78 iops 622 KB/s (0)
[  992.204352] dmatest: Started 1 threads using dma2chan5
[  992.215068] dmatest: dma2chan5-copy0: summary 1 tests, 0 failures 4587.15 iops 4587 KB/s (0)
[  992.217825] dmatest: Started 1 threads using dma2chan6
[  992.228584] dmatest: dma2chan6-copy0: summary 1 tests, 0 failures 4273.50 iops 4273 KB/s (0)
[  992.231715] dmatest: Started 1 threads using dma2chan7
[  992.241879] dmatest: dma2chan7-copy0: summary 1 tests, 0 failures 101.90 iops 407 KB/s (0)

I am currently using "dma2chan0" (at least trying to). Is this a valid choice?

I need to get the best performance as the FPGA provides sample data up to 50 MB/s.

Best Regards,

Gunther

[GLaure]

Do I have to assign A DMA channel in the boards dts file?

Currently i look like this. I am able to read from the FPGA using /dev/mem.

/* stm32-fmc2-ebi */
&fmc {
	pinctrl-names = "default", "sleep";
	pinctrl-0 = <&fmc_pins_mx>;
	pinctrl-1 = <&fmc_sleep_pins_mx>;
 	status = "okay";
 
	sram@0,0 {
		compatible = "mtd-ram";
		reg = <0 0x0 0x80000>;
		bank-width = <2>;
 
		/* Timing values are in nS */
		st,fmc2-ebi-cs-transaction-type = <0>;
		st,fmc2-ebi-cs-buswidth = <8>;
		st,fmc2-ebi-cs-address-setup-ns = <6>;
		st,fmc2-ebi-cs-address-hold-ns = <6>;
		st,fmc2-ebi-cs-data-setup-ns = <60>;
		st,fmc2-ebi-cs-data-hold-ns = <9>;
		st,fmc2-ebi-cs-bus-turnaround-ns = <20>;
 	};
 };