Re: can device drivers return non-ram via vm_ops->nopage?

[Jaroslav Kysela]

On Sat, 20 Mar 2004, Russell King wrote:

> The issues are:
> 
> 1. ALSA wants to mmap the buffer used to transfer data to/from the
>    card into user space.  This buffer may be direct-mapped RAM,
>    memory allocated via dma_alloc_coherent(), an on-device buffer,
>    or anything else.

We don't require to remap the mmio ring buffer (actually only RME32 has
a PCI memory window with the ring buffer, but this driver uses 
memcpy_(to|from)io already). So, we need to remap RAM and DMA pages
(should be special RAM also) only.

>    The user space mapping must likewise be DMA-coherent.
> 
>    Currently, ALSA just does virt_to_page() on whatever address it
>    feels like in its nopage() function, which is obviously not
>    acceptable for two out of the three specific cases above.

Yes.

> 2. ALSA wants to _coherently_ share data between the kernel-side
>    drivers, and user space ALSA library, mainly the DMA buffer
>    head/tail pointers so both kernel space and user space knows
>    when the buffer is full/empty.

Yes.

						Jaroslav

-----
Jaroslav Kysela <perex@xxxxxxx>
Linux Kernel Sound Maintainer
ALSA Project, SuSE Labs
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