Re: [comedi] Fail to use out-of-tree comedi on debian

On 30/09/2025 13:36, Ian Abbott wrote:
> On 30/09/2025 09:02, C=C3=A9dric Boudinet wrote:
>> Hello
>>
>> I would like to improve the comedi driver for the dt9812 card.
>> I a working on debian Trixie. I tried to rebuild and install using=20
>> dkms with the master version from git (https://github.com/Linux-=20
>> Comedi/ comedi/blob/master/INSTALL.md#running-comedi).
>> The build process and install works fine (modinfo loads comedi.ko.xz=20
>> and dt9812.ko.xz from /lib/modules/6.12.48+deb13-amd64/updates/dkms/).
>>
>> However when I plug the iocard, dmesg shows the following errors:
[snip]
>> And no /dev/comedi0 is created. Do you know where the problem is=20
>> coming from? Should I rebuild comedilib as well? Or maybe should I=20
>> rebuilt from the debian kernel source?
>>
>> Bests
>> Cedric
>=20
> I guess the cause is indicated by this message:
>=20
> [ 1108.696688] transfer buffer is on stack
>=20
> The Linux kernel in-tree Comedi USB drivers allocate USB command buffers=
=20
> from kmalloc memory, due to stack memory not being supported on some=20
> architectures for DMA.=C2=A0 I guess "some architectures" now includes=20
> x86-64, which it never used to.

I've pushed a commit to the Comedi GitHub repo to hopefully correct this=20
problem, based on code in the Linux kernel in-tree version of the driver=20
to replace the on-stack buffers with temporary kmalloc'ed buffers=20
(actually kzalloc to zero-fill the allocated buffers).

Please let me know if it works if you get the chance to test it.

There may be similar problems in the other out-of-tree USB Comedi=20
drivers, but I'm looking into that now.

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