[linux-dvb] bus control

Manu Abraham abraham.manu at gmail.com
Fri Jul 27 03:22:37 CEST 2007


On 7/27/07, Nick Andrew <nick-linuxtv at nick-andrew.net> wrote:
> On Thu, Jul 26, 2007 at 05:41:41PM +0400, Manu Abraham wrote:
> > That said, the firmware download is not too lengthy, but the Host when
> > handling 2 Transfers simultaeneously in both directions, the
> > performance might be degraded according to the vendor, though they do
> > not have actual figures.
>
> Can you serialize the two transfers with a mutex?

Serialization is not the case here, although serialization is needed
to handle the 2 demods
The communication goes through the Bus interface to the first demod
and from there to the second demod.

----------->Host------------>demod #0(MASTER)----------->demod #1(SLAVE)

If the host has 2 handle the 2 communications simultaneously, since it
has to handle the USB requests as well as control communication
through demod#0 to demod#1

It the case of the 2 stage copy, what you do is:

1) download fw

---------->Host

2) copy fw from Host to demod #1
Host disables demod#0 during the operation (transparent)

Host--------------->demod#1

so, the fw is temporarily cached in the Host, rather than a straight
download as in the very first (err..) diagram

Disabling the caching (ie fw copy, 2 stage process) causes an overhead
to the BIU, which the vendor says could affect effeciency/performance.
Here the firmware download in any case happens for one device at a
time only. Therefore a serialization employing a mutex doesn't bring
in any additional improvements as it _is_ already serialized.

Manu



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