Re: cx88 remote control event device

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

Mauro Carvalho Chehab wrote:
> Hi Jean,
> 
> Jean Delvare wrote:
>> Hi Andrzej,
>>
>> Last year, you submitted a fix for the cx88 remote control not behaving
>> properly on some cards. The fix works fine for me and lets me use my
>> remote control, and I am very grateful for this.
>>
>> However, I have noticed (using powertop) that the cx88 driver is waking
>> up the kernel 1250 times per second to handle the remote control. I
>> understand that it is needed for proper operation when the remote
>> control is in use. What I do not understand is why it still happens
>> when nobody uses the remote control. Even when no application has the
>> event device node opened, polling still happens.
>>
>> Can't we have the cx88 driver poll the remote control only when the
>> device node is opened? I believe this would save some power by allowing
>> the CPU to stay in higher C states.
> 
> The IR can be used even when nobody is opening the /dev/video device, as
> it is an input device that can be used to control other things, including
> the start of the video application.
> 
> That's said, it makes sense to only enable the polling when the /dev/input/event 
> device is opened. 
> 
> Btw, the same polling logic is also present on bttv and saa7134 drivers.
> 
> As I'm doing a large IR rework, with the addition of the IR core subsystem,
> and the patch for handing the open/close is very simple, I've already wrote
> a patch for saa7134, on my IR tree:
> 	http://git.linuxtv.org/mchehab/ir.git?a=commitdiff;h=2b1d3acdb48266f05b82923b8db06e6c7ada0c72
> 
> The change itself is very simple, although I've added some additional checks
> to avoid the risk of having an IRQ while IR is disabled.
> 
> I have one cx88 board on my IR test machine (although I need to find the IR sensor for the
> board I'm using there). If I find one that works, I'll try later to write a similar 
> code to cx88.
> 

Btw, I found one sensor here and started working with it. With the new code,
cx88 is generating lots of missing ticks. My IR debug log is full of those
messages:

[ 3276.764939] cx88[0] IR: Missed ticks 15                                      
[ 3276.768999] cx88[0] IR: Missed ticks 3                                       
[ 3276.772323] cx88[0] IR: Missed ticks 3                                       
[ 3276.789027] cx88[0] IR: Missed ticks 15                                      
[ 3276.793085] cx88[0] IR: Missed ticks 3                                       
[ 3276.796409] cx88[0] IR: Missed ticks 3                                       
[ 3276.813025] cx88[0] IR: Missed ticks 15                                      
[ 3276.816347] cx88[0] IR: Missed ticks 3                                       
[ 3276.816347] cx88[0] IR: Missed ticks 3                                       
[ 3276.837011] cx88[0] IR: Missed ticks 15                                      
[ 3276.840339] cx88[0] IR: Missed ticks 3                                       
[ 3276.845028] cx88[0] IR: Missed ticks 3                                       
[ 3276.861019] cx88[0] IR: Missed ticks 15                                      
[ 3276.864342] cx88[0] IR: Missed ticks 3                                       
[ 3276.869089] cx88[0] IR: Missed ticks 3                                       

This doesn't seem right, especially since this test machine is in text mode,
and there's nothing running there.

-- 

Cheers,
Mauro