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