Re: em28xx_isoc_dvb_max_packetsize for EM2884 (Terratec Cinergy HTC Stick)

Dennis Sperlich
2011-12-25T20:33:30Z

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On 25.12.2011 19:13, Mauro Carvalho Chehab wrote:
> On 25-12-2011 12:04, Dennis Sperlich wrote:
>> 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.
> The maximum packet size is described at the USB descriptors.
>
> The code at em28xx_set_alternate() seeks for the alternates and selects
> the one that will get the best alternate for the analog mode.
>
> There, you'll see a code that gets the best alternate for analog,
> and selects the proper packet size for it.
>
> For DVB, it should be a little different, as, on DVB, the driver doesn't
> know, in advance, what's the streaming rate. So, the driver needs to get
> a high enough packet size to fit for the bandwidth needs.
>
> Also, for DVB, the driver does:
> usb_set_interface(dev->udev, 0, 1);
>
> (e. g. it always use alternate 1)
>
> So, in thesis, that function could be as simple as:
> dev->alt_max_pkt_size[1];
>
> (if the max packet size for alternate 1 would work for all chips)
>
> Or, eventually, the code might be using other alternates for HD,
> but I'm not sure if those chipsets support a different alternate for DVB.
I just tried, replacing
max_dvb_packet_size = em28xx_isoc_dvb_max_packetsize(dev);
by
max_dvb_packet_size = dev->alt_max_pkt_size[1];

but it did not work. Was this the correct replacement?

printk(KERN_INFO "dev->alt_max_pkt_size[1] is
%i\n",dev->alt_max_pkt_size[1]);

then said, dev->alt_max_pkt_size[1] is 0.

I also attachted a lsusb -v output for the Terratec Cinergy HTC Stick.
I don't know, which of these endpoints the dvb-c part is, but it may be
anyway usefull.

Regard,
Dennis

[-- Attachment #2: lsusb --]
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