Re: Details about DVB frontend API

[Mauro Carvalho Chehab <mchehab@redhat.com>]

Mauro Carvalho Chehab wrote:
> Michael Krufky wrote:
>> On Fri, Dec 4, 2009 at 3:02 PM, VDR User <user.vdr@gmail.com> wrote:
>>> No activity in this thread for 2 weeks now.  Has there been any progress?
> 
>> I have stated that I like Manu's proposal, but I would prefer that the
>> get_property (s2api) interface were used, because it totally provides
>> an interface that is sufficient for this feature.
> 
> I've ported Manu's proposal to S2API way of handling it. It is just compiled
> only. I haven't test it yet on a real driver.
> 
> Comments?
> 
> ---
> 
> Add support for frontend statistics via S2API
> 
> The current DVB V3 API to handle statistics has two issues:
> 	- Retrieving several values can't be done atomically;
> 	- There's no indication about scale information.
> 
> This patch solves those two issues by adding a group of S2API
> that handles the needed statistics operations. It basically ports the
> proposal of Manu Abraham <abraham.manu@gmail.com> To S2API.
> 
> As the original patch, both of the above issues were addressed.
> 
> In order to demonstrate the changes on an existing driver for the new API, I've
> implemented it at the cx24123 driver.
> 
> There are some advantages of using this approach over using the static structs
> of the original proposal:
> 	- userspace can select an arbitrary number of parameters on his get request;
> 	- the latency to retrieve just one parameter is lower than retrieving
> several parameters. On the cx24123 example, if user wants just signal strength,
> the latency is the same as reading one register via i2c bus. If using the original
> proposal, the latency would be 6 times worse, since you would need to get 3 properties
> at the same time;
> 	- the latency for reading all 3 parameters at the same time is equal to
> the latency of the original proposal;
> 	- if newer statistics parameters will be needed in the future, it is just
> a matter of adding additional S2API command/value pairs;
> 	- the DVB V3 calls can be easily implemented as a call to the new get_stats ops,
> without adding extra latency time.

In time:

I only wrote the get callback. It could be interesting to implement also the set callback
for the DTV_FE*_UNIT parameters if there are some cases where the same driver can provide
a different set of units/parameters. This way, it is possible for userspace to
negotiate what parameter type he wants, on such drivers.
> 
> Thanks to Manu Abraham <abraham.manu@gmail.com> for his initial proposal.
> 

Cheers,
Mauro.