[alsa-devel] [PATCH] ASoC: core: Only kmemdup binary control buffer if masking

Charles Keepax ckeepax at opensource.wolfsonmicro.com
Wed Apr 2 16:49:20 CEST 2014

On Wed, Apr 02, 2014 at 03:41:03PM +0100, Mark Brown wrote:
> On Wed, Apr 02, 2014 at 03:17:05PM +0100, Charles Keepax wrote:
> > When writing a binary control we may apply a mask to the first register,
> > as this requires modifying the data the buffer is duplicated, currently
> > this is done for all binary control writes. As most binary controls
> > don't use the mask facility and thus can freely use the original buffer,
> > avoid the kmemdup for these cases.
> No, that's not why we're duplicating...
> > -	data = kmemdup(ucontrol->value.bytes.data, len, GFP_KERNEL | GFP_DMA);
> ...note the GFP_DMA there, it's about ensuring that the buffer is
> DMAable since the underlying APIs end up wanting that (or will for
> larger coefficient blocks anyway).  What would be slightly more
> efficient in the success case would be to do a kmalloc() then
> copy_from_user() into that block allowing us to bypass the copy.

Ah... thanks sorry about the noise.


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