On Sat, 8 Jan 2022, 14:37 Sadanand Warrier, 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 wrote: > > > > On Tue, 21 Dec 2021, 15:36 Sadanand Warrier, > 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 > > >