Re: em28xx_isoc_dvb_max_packetsize for EM2884 (Terratec Cinergy HTC Stick)

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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
Bus 001 Device 009: ID 0ccd:00b2 TerraTec Electronic GmbH 
Device Descriptor:
  bLength                18
  bDescriptorType         1
  bcdUSB               2.00
  bDeviceClass            0 (Defined at Interface level)
  bDeviceSubClass         0 
  bDeviceProtocol         0 
  bMaxPacketSize0        64
  idVendor           0x0ccd TerraTec Electronic GmbH
  idProduct          0x00b2 
  bcdDevice            1.00
  iManufacturer           2 TERRATEC
  iProduct                1 Cinergy_HTC_Stick
  iSerial                 3 02?TERRATE
  bNumConfigurations      1
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    wTotalLength          305
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      (Bus Powered)
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    Interface Descriptor:
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      bInterfaceNumber        0
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      bNumEndpoints           4
      bInterfaceClass       255 Vendor Specific Class
      bInterfaceSubClass      0 
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      iInterface              0 
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x81  EP 1 IN
        bmAttributes            3
          Transfer Type            Interrupt
          Synch Type               None
          Usage Type               Data
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        bInterval              11
      Endpoint Descriptor:
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        bDescriptorType         5
        bEndpointAddress     0x82  EP 2 IN
        bmAttributes            1
          Transfer Type            Isochronous
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      Endpoint Descriptor:
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      Endpoint Descriptor:
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    Interface Descriptor:
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      Endpoint Descriptor:
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        bEndpointAddress     0x81  EP 1 IN
        bmAttributes            3
          Transfer Type            Interrupt
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        wMaxPacketSize     0x0001  1x 1 bytes
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      Endpoint Descriptor:
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        bDescriptorType         5
        bEndpointAddress     0x82  EP 2 IN
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          Transfer Type            Isochronous
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      Endpoint Descriptor:
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          Transfer Type            Isochronous
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      Endpoint Descriptor:
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          Transfer Type            Isochronous
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        wMaxPacketSize     0x03ac  1x 940 bytes
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      Endpoint Descriptor:
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      Endpoint Descriptor:
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        bInterval               1
      Endpoint Descriptor:
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        wMaxPacketSize     0x0001  1x 1 bytes
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      Endpoint Descriptor:
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        bEndpointAddress     0x82  EP 2 IN
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      Endpoint Descriptor:
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        bDescriptorType         5
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          Transfer Type            Isochronous
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        wMaxPacketSize     0x00c4  1x 196 bytes
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      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x84  EP 4 IN
        bmAttributes            1
          Transfer Type            Isochronous
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          Usage Type               Data
        wMaxPacketSize     0x03ac  1x 940 bytes
        bInterval               1
    Interface Descriptor:
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      Endpoint Descriptor:
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        bInterval               1
    Interface Descriptor:
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      bInterfaceClass       255 Vendor Specific Class
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      Endpoint Descriptor:
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          Transfer Type            Interrupt
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        bInterval              11
      Endpoint Descriptor:
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      Endpoint Descriptor:
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        bDescriptorType         5
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        bmAttributes            1
          Transfer Type            Isochronous
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        wMaxPacketSize     0x00c4  1x 196 bytes
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      Endpoint Descriptor:
        bLength                 7
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          Transfer Type            Isochronous
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      bInterfaceClass       255 Vendor Specific Class
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      Endpoint Descriptor:
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        bDescriptorType         5
        bEndpointAddress     0x81  EP 1 IN
        bmAttributes            3
          Transfer Type            Interrupt
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      Endpoint Descriptor:
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      Endpoint Descriptor:
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          Transfer Type            Isochronous
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      Endpoint Descriptor:
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      Endpoint Descriptor:
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          Transfer Type            Interrupt
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        wMaxPacketSize     0x0001  1x 1 bytes
        bInterval              11
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x82  EP 2 IN
        bmAttributes            1
          Transfer Type            Isochronous
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        wMaxPacketSize     0x1400  3x 1024 bytes
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      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
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        bmAttributes            1
          Transfer Type            Isochronous
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      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
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          Transfer Type            Isochronous
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        wMaxPacketSize     0x03ac  1x 940 bytes
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Device Qualifier (for other device speed):
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  bDeviceClass            0 (Defined at Interface level)
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  bMaxPacketSize0        64
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Device Status:     0x0000
  (Bus Powered)

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