Contiguous Memory Allocator (CMA)
sadanandwarrier at gmail.com
Sat Jan 8 17:49:18 EST 2022
I haven't done it because I haven't had time and CONFIG_DMA_CMA has not
been enabled in the kernel I was fooling with. Yes I do know how to build
Thanks for all the help. Once I get it working I'll let you know.
On Sat, Jan 8, 2022, 17:14 FMDF <fmdefrancesco at gmail.com> wrote:
> On Sat, 8 Jan 2022, 14:37 Sadanand Warrier, <sadanandwarrier at gmail.com>
>> Hello Fabio
>> Thanks for the response. I had already accessed that link that you
>> have pasted. Michal Nazarewicz also has a few other points on using
>> When I tried to use the API after setting cma=128M on the kernel boot
>> command line and booted the kernel, the api returned without
>> allocating memory
>> when the driver was installed.
>> The dmesg shows that 128M was reserved for CMA but dma_alloc_coherent
>> It seems that default CentOS and perhaps Ubuntu kernels are not
>> compiled with CONFIG_DMA_CMA=yes for the dma_alloc_coherent to work.
>> I'm not sure if this is a valid assumption. I haven't tried
>> recompiling the kernel yet with that option set.
>> From what I have managed to eke out we need CONFIG_CMA=yes and
>> CONFIG_DMA_CMA=yes too.
> If I recall it well, I think they are needed. Why haven't you yet checked?
> I assume that you know how to change your .config, re-build the kernel and
> the modules and install everything in the right places. Don't you?
> Just grep the ".config" of your distro. It should be placed in /boot/
> with a name like "config-`uname -r`" or in /usr/src/linux/ with its true
> name (.config) and see if those options are enabled. Or you may use
> directly "make menuconfig" and search with its special keys. Then "make -jN
> && sudo make modules_install install" (and hope that installkernel is not
> broken like it has been in openSUSE Tumbleweed for weeks). :(
> I'm not an expert about this particular subject, so if they have already
> been enabled I cannot help you with more than the above information. That
> article in lwn.net is everything I've studied about this subject and I
> haven't ever used it in kernel programming.
> Fabio M. De Francesco
>> On Sat, 8 Jan 2022 at 07:23, FMDF <fmdefrancesco at gmail.com> wrote:
>> > On Tue, 21 Dec 2021, 15:36 Sadanand Warrier, <sadanandwarrier at gmail.com>
>> >> Hello
>> >> Is CMA still supported as described in this document
>> >> https://lwn.net/Articles/396707/ ?
>> > Yes, it is.
>> > Read the following instructions on how to use that feature:
>> > "A deep dive into CMA" at
>> > https://lwn.net/Articles/486301/
>> > Regards,
>> > Fabio M. De Francesco
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