I'm writing an ALSA sound card driver, for a card that does not support DMA, thus the CPU need to do the copying to and from the onboard buffer. ALSA allows for optional mmap'd access, that is accessing the in memory dma buffer directly from user space. However, for this card that does not support DMA, it would be best to mmap its IO memory directly, this way I get rid of a copy in the interrupt handler to an intermediate kernel buffer. This should be possible on the i386 as far as I know. I use a 2.2.14 kernel, and ioremap (also tested ioremap_nocache) to relocate the IO memory. In kernel space it works fine to access the ioremap'd area just like any other kernel buffer. However, when the ioremap'd area is mmap'd from user space, problems occur. In user space: when the memory is read, all bytes are always 0xFF, and when written to, nothing happens (the memory being on the sound card is unchanged). I have two questions: (1) why is this happening? (2) is it possible to make it work? Please reply to my address directly, since I'm not on the mailing list. /Anders Torger - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] Please read the FAQ at http://www.tux.org/lkml/
