[alsa-devel] [PATCH v4 5/6] core: add support for compress_offload

Vinod Koul vinod.koul at linux.intel.com
Tue Dec 13 18:53:40 CET 2011

On Tue, 2011-12-13 at 21:32 +0530, Nallasellan, Singaravelan wrote:
> > 
> > Again, please read the related discussion on the list.
> > 
> > Compressed devices will not have direction associated with them . They can be
> > opened in any mode depending on the mode the DSP supports.
> > So /dev/snd/comprC0D0 can be either playback or capture device.
> > So a device can be ONLY opened with O_WRONLY or O_RDONLY.
> > 
> Nice, Does it look like a hack hack hack...
Care to elaborate your comment?

> > > O_NONBLOCK is not tested here for non-blocking support.
> > Why should it be?
> > 1) Any blocking and non blocking should be handled in user space
> > 2) Nevertheless, that is not supported, HINT: read the documentation
> > 
> This is not as per the write system call definition as I understand.
> Look like we redefine the
> system call here. Support it in the standard way.
Your argument is entirely bogus.
What do you mean by that? Noone is changing a system call.
For this device O_NONBLOCK is not supported thats it!!! How does that
violate a system call. 
There are many other flags which some device support and some don't.

> > Yes currently write is allowed only once and we *normally* expect a START call. I am
> > not sure why someone would need to call "smaller"
> > writes multiple times. Remember this is compressed offload where we ideally want
> > larger chunks of data otherwise there is no point in using this.
> The code allows this to happen.  Is there any minimum size documented anywhere? 
That's whatever dsp supports

> > > What is the maximum number of fragments supported?
> > Whatever dsp supports
> IMHO, compress-core needs to query it from each driver and allocate memory 
> only if the supported fragments is greater than requested fragments. 
user library should query the format and other details supported at
open. So these checks are anyway made their.
Nevertheless, this can be taken care in core as well but there is always
a question of how much check to do.

> > 
> > > Can we check the fragments to that limit?
> > Yes, can be checked here as well but I prefer to do these checks in userspace library
> Think the driver needs to check and return error if it is not within the maximum
> supported by the driver.
Where is driver coming here?


More information about the Alsa-devel mailing list