On Tue, 05 Nov 2019 19:17:40 +0100, Sridharan, Ranjani wrote: > > > > > > Hi Takashi, > > > > I have a question about the usage of snd_dma_alloc_pages() with the > > SNDRV_DMA_TYPE_DEV type. I am working on adding a platform-device for > > audio which is a child device of the top-level PCI device in SOF. > > When I use the handle for the platform-device as the "dev" argument for > > snd_dma_alloc_pages(), the dma alloc fails on some platforms (ex: Ice > > Lake). But it works fine if I use the top-level PCI device instead. > > Why would that be? Are there any restrictions to what devices can be > > used for dma alloc? > > This pretty much depends on the device. Basically the ALSA memalloc > stuff simply calls dma_alloc_coherent() if the buffer type is > SNDRV_DMA_TYPE_DEV, and the rest goes deeply into the code in > kernel/dma/*. > > My wild guess is that the significant difference in your case is about > the DMA coherence mask set on the device. As default the platform > device keeps 32bit DMA while the modern PCI drivers often sets up > 64bit DMA mask. > > Thanks, Takashi. So, in this case, would you recommend to always use the PCI > device for dma alloc? Yes, if the PCI bus is used in the backend, using the PCI device is a better choice. Takashi _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx https://mailman.alsa-project.org/mailman/listinfo/alsa-devel
