Re: em28xx_isoc_dvb_max_packetsize for EM2884 (Terratec Cinergy HTC Stick)

[Dennis Sperlich <dsperlich@googlemail.com>]

On 25.12.2011 11:52, Mauro Carvalho Chehab wrote:
> On 24-12-2011 19:58, Dennis Sperlich wrote:
>> Hi,
>>
>> I have a Terratec Cinergy HTC Stick an tried the new support for the DVB-C part. It works for SD material (at least for free receivable stations, I tried afair only QAM64), but did not for HD stations (QAM256). I have only access to unencrypted ARD HD, ZDF HD and arte HD (via KabelDeutschland). The HD material was just digital artefacts, as far as mplayer could decode it. When I did a dumpstream and looked at the resulting file size I got something about 1MB/s which seems a little too low, because SD was already about 870kB/s. After looking around I found a solution in increasing the isoc_dvb_max_packetsize from 752 to 940 (multiple of 188). Then an HD stream was about 1.4MB/s and looked good. I'm not sure, whether this is the correct fix, but it works for me.
>>
>> If you need more testing pleas tell.
>>
>> Regards,
>> Dennis
>>
>>
>>
>> index 804a4ab..c518d13 100644
>> --- a/drivers/media/video/em28xx/em28xx-core.c
>> +++ b/drivers/media/video/em28xx/em28xx-core.c
>> @@ -1157,7 +1157,7 @@ int em28xx_isoc_dvb_max_packetsize(struct em28xx *dev)
>>                   * FIXME: same as em2874. 564 was enough for 22 Mbit DVB-T
>>                   * but not enough for 44 Mbit DVB-C.
>>                   */
>> -               packet_size = 752;
>> +               packet_size = 940;
>>          }
>>
>>          return packet_size;
> As you can see there at the code, the packet size depends on the chipset, as
> not all will support 940 for packet size.
>
> Could you please provide us what was the chip detected id?
>
> It should be a message on your dmesg like:
>
> 	chip ID is em2870
> or
> 	em28xx chip ID = 38
>
> The patch should change it only for your specific chipset model, in order to
> avoid regressions to other supported chipsets, like:
>
> int em28xx_isoc_dvb_max_packetsize(struct em28xx *dev)
> {
>          unsigned int chip_cfg2;
>          unsigned int packet_size;
>
>          switch (dev->chip_id) {
>          case CHIP_ID_EM2710:
>          case CHIP_ID_EM2750:
>          case CHIP_ID_EM2800:
>          case CHIP_ID_EM2820:
> ...
> 	case CHIP_ID_foo:
> 		packet_size = 940;
> ...
>          }
>
>          return packet_size;
> }
>
> The case you're touching seems to be for em2884, but the switch covers both
> em2884 and em28174 (plus the default for newer chipsets).

dmesg says: em28xx #0: chip ID is em2884

so a patch would be more like:

index 804a4ab..9280251 100644
--- a/drivers/media/video/em28xx/em28xx-core.c
+++ b/drivers/media/video/em28xx/em28xx-core.c
@@ -1151,6 +1151,8 @@ int em28xx_isoc_dvb_max_packetsize(struct em28xx *dev)
                 packet_size = 564;
                 break;
         case CHIP_ID_EM2884:
+               packet_size = 940;
+               break;
         case CHIP_ID_EM28174:
         default:
                 /*

> Maybe Michael/Devin may have something to say, with regards to a way to detect
> the maximum supported packet size by each specific em28xx model.

This would be fine, I tried also 1128 (6 times 188), but then mplayer 
did not play any more. I then tried 1034, but then I got the message " 
submit of urb 0 failed (error=-90)", so I guess there have to be integer 
multiples of 188.

Regards,
Dennis