Re: [PATCH RFC] media: em28xx: don't use coherent buffer for DMA transfers

[Mauro Carvalho Chehab <mchehab@s-opensource.com>]

Em Wed, 28 Feb 2018 09:49:12 -0500
Devin Heitmueller <dheitmueller@kernellabs.com> escreveu:

> On Tue, Feb 27, 2018 at 12:42 PM, Mauro Carvalho Chehab
> <mchehab@s-opensource.com> wrote:
> > While coherent memory is cheap on x86, it has problems on
> > arm. So, stop using it.
> >
> > Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
> > ---
> >
> > I wrote this patch in order to check if this would make things better
> > for ISOCH transfers on Raspberry Pi3. It didn't. Yet, keep using
> > coherent memory at USB drivers seem an overkill.
> >
> > So, I'm actually not sure if we should either go ahead and merge it
> > or not.
> >
> > Comments? Tests?
> 
> For what it's worth, while I haven't tested this patch you're
> proposing, I've been running what is essentially the same change in a
> private tree for several years in order for the device to work better
> with several TI Davinci SOC platforms.

Good to know! I guess then it is worth applying it. Btw, while here,
I'm wandering if it should keep using URB_ISO_ASAP flag or not. On
my tests, for DVB, it seems to be working both ways. Didn't test
analog TV yet.

Thanks,
Mauro