Re: Contiguous Memory Allocator (CMA)

[Sadanand Warrier <sadanandwarrier@gmail.com>]

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Hello Fabio,
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
the kernel.
Thanks for all the help. Once I get it working I'll let you know.
Cheerio
S

On Sat, Jan 8, 2022, 17:14 FMDF <fmdefrancesco@gmail.com> wrote:

> On Sat, 8 Jan 2022, 14:37 Sadanand Warrier, <sadanandwarrier@gmail.com>
> wrote:
>
>> 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
>> CMA.
>> 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
>> failed.
>> 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.
>
> Regards,
>
> Fabio M. De Francesco
>
>
>> Thanks
>> S
>>
>>
>> On Sat, 8 Jan 2022 at 07:23, FMDF <fmdefrancesco@gmail.com> wrote:
>> >
>> > On Tue, 21 Dec 2021, 15:36 Sadanand Warrier, <sadanandwarrier@gmail.com>
>> wrote:
>> >>
>> >> 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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