quoted

dmas = <& axi_dma_0 1>
dma-names = "axi_dma_0"

quoted

Our device-tree entry looks like this:
    axi_dma_0: dma@80002000 {
        status = "okay";
        #dma-cells = <1>;
        compatible = "xlnx,axi-dma-1.00.a";
        interrupt-parent = <&gic>;
        interrupts = <0 89 4>;
        reg = <0x0 0x80002000 0x0 0x1000>;
        xlnx,addrwidth = <0x20>;
        clocks = <&zynqmp_clk LPD_LSBUS>, <&zynqmp_clk LPD_LSBUS>,
<&zynqmp_clk LPD_LSBUS>, <&zynqmp_clk LPD_LSBUS>;
        clock-names = "s_axi_lite_aclk", "m_axi_sg_aclk",
"m_axi_mm2s_aclk", "m_axi_s2mm_aclk";
        dma-channel@80002030 {
            compatible = "xlnx,axi-dma-s2mm-channel";
            dma-channels = <0x1>;
            interrupts = <0 89 4>;
            xlnx,datawidth = <0x20>;
            xlnx,device-id = <0x0>;
        };
    };

This is on a 5.10.1 kernel on arm64 zynqmp hardware.

The second issue goes a little further back to commit e81274cd6b526
'dmaengine: add support to dynamic register/unregister of channels'.
After this commit even just removing the module 'rmmod xilinx_dma',
without ever using it, results in a kernel oops like this:
[   37.214568] xilinx-vdma 80002000.dma: ch 0: SG disabled
[   37.219807] xilinx-vdma 80002000.dma: WARN: Device release is not
defined so it is not safe to unbind this driver while in use
[   37.231299] xilinx-vdma 80002000.dma: Xilinx AXI DMA Engine Driver
Probed!!
[   42.100660] Unable to handle kernel paging request at virtual
address dead000000000108
[   42.108598] Mem abort info:
[   42.111393]   ESR = 0x96000044
[   42.114443]   EC = 0x25: DABT (current EL), IL = 32 bits
[   42.119744]   SET = 0, FnV = 0
[   42.122794]   EA = 0, S1PTW = 0
[   42.125918] Data abort info:
[   42.128789]   ISV = 0, ISS = 0x00000044
[   42.132617]   CM = 0, WnR = 1
[   42.135577] [dead000000000108] address between user and kernel
address ranges
[   42.142705] Internal error: Oops: 96000044 [#1] SMP
[   42.147566] Modules linked in: xilinx_dma(-) clk_xlnx_clock_wizard
uio_pdrv_genirq
[   42.155139] CPU: 1 PID: 2075 Comm: rmmod Not tainted
5.10.1-00026-g3a2e6dd7a05-dirty #192
[   42.163302] Hardware name: Enclustra XU5 SOM (DT)
[   42.167992] pstate: 40000005 (nZcv daif -PAN -UAO -TCO BTYPE=--)
[   42.173996] pc : xilinx_dma_chan_remove+0x74/0xa0 [xilinx_dma]
[   42.179815] lr : xilinx_dma_chan_remove+0x70/0xa0 [xilinx_dma]
[   42.185636] sp : ffffffc01112bca0
[   42.188935] x29: ffffffc01112bca0 x28: ffffff80402ea640
[   42.194238] x27: 0000000000000000 x26: 0000000000000000
[   42.199542] x25: 0000000000000000 x24: 0000000000000000
[   42.204845] x23: 0000000000000000 x22: 0000000000000000
[   42.210149] x21: ffffffc0088a2028 x20: ffffff8040c08410
[   42.215452] x19: ffffff80423fa480 x18: ffffffffffffffff
[   42.220756] x17: 0000000000000000 x16: 0000000000000000
[   42.226059] x15: ffffffc010ce88c8 x14: 0000000000000040
[   42.231363] x13: ffffff0000000000 x12: ffffffffffffffff
[   42.236667] x11: 0000000000000028 x10: ffffffff7fffffff
[   42.241970] x9 : ffffffff00f0dfe0 x8 : 0000000000000000
[   42.247273] x7 : ffffffc010da4000 x6 : 0000000000000000
[   42.252577] x5 : 0000000000210d00 x4 : ffffffc010da4da0
[   42.257881] x3 : ffffff80423fa578 x2 : 0000000000000000
[   42.263184] x1 : dead000000000100 x0 : dead000000000122
[   42.268488] Call trace:
[   42.270923]  xilinx_dma_chan_remove+0x74/0xa0 [xilinx_dma]
[   42.276399]  xilinx_dma_remove+0x3c/0x70 [xilinx_dma]
[   42.281446]  platform_drv_remove+0x24/0x38
[   42.285530]  device_release_driver_internal+0xec/0x1a8
[   42.290659]  driver_detach+0x64/0xd8
[   42.294226]  bus_remove_driver+0x58/0xb8
[   42.298133]  driver_unregister+0x30/0x60
[   42.302048]  platform_driver_unregister+0x14/0x20
[   42.306744]  xilinx_vdma_driver_exit+0x18/0x978 [xilinx_dma]
[   42.312396]  __arm64_sys_delete_module+0x1e4/0x270
[   42.317178]  el0_svc_common.constprop.4+0x68/0x170
[   42.321959]  do_el0_svc+0x70/0x90
[   42.325267]  el0_svc+0x14/0x20
[   42.328313]  el0_sync_handler+0x90/0xb8
[   42.332141]  el0_sync+0x158/0x180
[   42.335442] Code: 95dfce29 9103c260 95de7ffb a9490261 (f9000420)
[   42.341525] ---[ end trace dbd90aeb5ca71943 ]---

So if I use the 04c2bc2bede1 (commit before 14ccf0aab46e) version of
xilinx_dma.c and never remove the module then it is working with the
5.10.1 kernel.

Ok, we will analyze this issue and report back the findings.

+ Dave

I was able to reproduce this crash on the unloading xilinx_dma module.
This is introduced due to the e81274cd6b526 mainline commit added
in the 5.6 kernel version. The crash is coming from -

xilinx_dma_chan_remove+0x74/0xa0:
__list_del at ./include/linux/list.h:112
(inlined by) __list_del_entry at./include/linux/list.h:135
(inlined by) list_del at ./include/linux/list.h:146
(inlined by) xilinx_dma_chan_remove at drivers/dma/xilinx/xilinx_dma.c:2546

Looking into e81274cd6b526 commit - It deletes channel device_node entry.
Same channel device_node entry is also deleted in  xilinx_dma_chan_remove
as a result we see this crash.

@@ -993,12 +1007,22 @@ static

void __dma_async_device_channel_unregister(struct dma_device *device,
                  "%s called while %d clients hold a reference\n",
                  __func__, chan->client_count);
        mutex_lock(&dma_list_mutex);
+       list_del(&chan->device_node);
+       device->chancnt--;

I will let Dave comment on the background of this change.  In
dmaengine driver - we are adding channel device node entry
so deleting it in the exit path looks fine to me. Also, I checked
other dma drivers are also deleting channel device_node entry
in .remove so it likely a common problem.

quoted

quoted

Hopefully, this will be clear to someone how these issues can be
resolved. In general we've been very happy using the xilinx dma.

I'm not subscribed to the linux-kernel ML so if you need any further
info or testing just keep me in the to: list.

thanks,
Paul