Re: dmaengine : xilinx_dma two issues
From: Lars-Peter Clausen
Date: Mon Jan 11 2021 - 10:34:21 EST
On 1/11/21 10:32 AM, Michal Simek wrote:
Hi Lars,
On 10. 01. 21 16:43, Lars-Peter Clausen wrote:
On 1/10/21 4:16 PM, Paul Thomas wrote:
On Fri, Jan 8, 2021 at 1:36 PM Radhey Shyam Pandey
<radheys@xxxxxxxxxx> wrote:
-----Original Message-----
From: Paul Thomas <pthomas8589@xxxxxxxxx>
Sent: Friday, January 8, 2021 9:27 PM
To: Radhey Shyam Pandey <radheys@xxxxxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>; Vinod Koul
<vkoul@xxxxxxxxxx>; Michal Simek <michals@xxxxxxxxxx>; Matthew Murrian
<matthew.murrian@xxxxxxxxxx>; Romain Perier
<romain.perier@xxxxxxxxx>; Krzysztof Kozlowski <krzk@xxxxxxxxxx>; Marc
Ferland <ferlandm@xxxxxxxxx>; Sebastian von Ohr
<vonohr@xxxxxxxxxxx>; dmaengine@xxxxxxxxxxxxxxx; Linux ARM <linux-
arm-kernel@xxxxxxxxxxxxxxxxxxx>; linux-kernel <linux-
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Subject: Re: dmaengine : xilinx_dma two issues
Hi All,
On Fri, Jan 8, 2021 at 2:13 AM Radhey Shyam Pandey <radheys@xxxxxxxxxx>
wrote:
-----Original Message-----
From: Radhey Shyam Pandey
Sent: Monday, January 4, 2021 10:50 AM
To: Paul Thomas <pthomas8589@xxxxxxxxx>; Dan Williams
<dan.j.williams@xxxxxxxxx>; Vinod Koul <vkoul@xxxxxxxxxx>; Michal
Simek <michals@xxxxxxxxxx>; Matthew Murrian
<matthew.murrian@xxxxxxxxxx>; Romain Perier
<romain.perier@xxxxxxxxx>; Krzysztof Kozlowski <krzk@xxxxxxxxxx>;
Marc Ferland <ferlandm@xxxxxxxxx>; Sebastian von Ohr
<vonohr@xxxxxxxxxxx>; dmaengine@xxxxxxxxxxxxxxx; Linux ARM <linux-
arm-kernel@xxxxxxxxxxxxxxxxxxx>; linux-kernel <linux-
kernel@xxxxxxxxxxxxxxx>; Shravya Kumbham <shravyak@xxxxxxxxxx>; git
<git@xxxxxxxxxx>
Subject: RE: dmaengine : xilinx_dma two issues
-----Original Message-----
From: Paul Thomas <pthomas8589@xxxxxxxxx>
Sent: Monday, December 28, 2020 10:14 AM
To: Dan Williams <dan.j.williams@xxxxxxxxx>; Vinod Koul
<vkoul@xxxxxxxxxx>; Michal Simek <michals@xxxxxxxxxx>; Radhey
Shyam Pandey <radheys@xxxxxxxxxx>; Matthew Murrian
<matthew.murrian@xxxxxxxxxx>; Romain Perier
<romain.perier@xxxxxxxxx>;
Krzysztof Kozlowski <krzk@xxxxxxxxxx>; Marc Ferland
<ferlandm@xxxxxxxxx>; Sebastian von Ohr <vonohr@xxxxxxxxxxx>;
dmaengine@xxxxxxxxxxxxxxx; Linux ARM <linux-
arm-kernel@xxxxxxxxxxxxxxxxxxx>; linux-kernel <linux-
kernel@xxxxxxxxxxxxxxx>
Subject: dmaengine : xilinx_dma two issues
Hello,
I'm trying to get the 5.10 kernel up and running for our system,
and I'm running into a couple of issues with xilinx_dma.
+ (Xilinx mailing list)
Thanks for bringing the issues to our notice. Replies inline.
First, commit 14ccf0aab46e 'dmaengine: xilinx_dma: In dma channel
probe fix node order dependency' breaks our usage. Before this
commit a
call to:
dma_request_chan(&indio_dev->dev, "axi_dma_0"); returns fine, but
after that commit it returns -19. The reason for this seems to be
that the only channel that is setup is channel 1 (chan->id is 1 in
xilinx_dma_chan_probe()).
However in
of_dma_xilinx_xlate() chan_id is gets set to 0 (int chan_id =
dma_spec-
args[0];), which causes the:
!xdev->chan[chan_id]
test to fail in of_dma_xilinx_xlate()
What is the channel number passed in dmaclient DT?
Is this a question for me?
Yes, please also share the dmaclient DT client node. Need to see
channel number passed to dmas property. Something like below-
dmas = <& axi_dma_0 1>
dma-names = "axi_dma_0"
OK, I think I need to revisit this and clean it up some. Currently In
the driver (a custom iio adc driver) it is hard coded:
dma_request_chan(&indio_dev->dev, "axi_dma_0");
However, the DT also has the entries (currently unused by the driver):
dmas = <&axi_dma_0 0>;
dma-names = "axi_dma_0";
I'll go back and clean up our driver to do something like
adi-axi-adc.c does:
if (!device_property_present(dev, "dmas"))
return 0;
if (device_property_read_string(dev, "dma-names", &dma_name))
dma_name = "axi_dma_0";
Should the dmas node get used by the driver? I see the second argument
is: '0' for write/tx and '1' for read/rx channel. So I should be
setting this to 1 like this?
dmas = <&axi_dma_0 1>;
dma-names = "axi_dma_0";
But where does that field get used?
This got broken in "dmaengine: xilinx_dma: In dma channel probe fix node
order dependency"
<https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=14ccf0aab46e1888e2f45b6e995c621c70b32651>.
Before if there was only one channel that channel was always at index 0.
Regardless of whether the channel was RX or TX. But after that change
the RX channel is always at offset 1, regardless of whether the DMA has
one or two channels. This is a breakage in ABI.
If you have the choice I'd recommend to not use the Xilinx DMA, it gets
broken pretty much every other release.
I expect that you are talking about Xilinx releases and I hope that this
has changed over times when most of changes are upstreamed already. The
patch above you are referencing has been applied by Vinod and he is
checking patches a lot. If there is a problem and any breakage it needs
to be fixed. And bugs happen all the time and we have a way how to work
with it.
I don't know if it has gotten better. When I upgrade to a new release
what takes up most of the time is figuring out why the Xilinx DMA
doesn't work anymore. Its been like this for years.
If you see there any issue please report them and let's fix them and
continue on this topic from technical point of view.
In connection to this problem what are you suggesting? Just revert this
patch or fix ordering differently? Would be good to provide your
suggestion and fix it.
Reverting would re-introduce the issue the patch was supposed to fix.
The would have been to use index 0 for the channel if there is only one
channel. If there are two channels use 0 for TX and 1 for RX.
The problem is that the change has been around for a while and restoring
the previous behavior will break users that are expecting the new
behavior. It is a bit of a catch-22.
- Lars