Re: WinTV-HVR-1400: scandvb (and kaffeine) fails to find any channels

[Chris Clayton <chris2553@googlemail.com>]

On 02/03/13 00:03, Chris Clayton wrote:
>
>
> On 02/01/13 21:07, Devin Heitmueller wrote:
>> On Fri, Feb 1, 2013 at 4:03 PM, Chris Clayton
>> <chris2553@googlemail.com> wrote:
>>> Yes, I noticed that but even with the tuning timeout set at medium or
>>> longest, I doesn't find any channels. However, I've been following
>>> the debug
>>> messages through the code and ended up at
>>> drivers/media/pci/cx23885/cx23885-i2c.c.
>>>
>>> I've found that by amending I2C_WAIT_DELAY from 32 to 64, I get improved
>>> results from scanning. With that delay doubled, scandvb now finds 49
>>> channels over 3 frequencies. That's with all debugging turned off, so no
>>> extra delays provided by the production of debug messages.
>>>
>>> I'll play around more tomorrow and update then.
>>
>> It could be that the cx23885 driver doesn't properly implement I2C
>> clock stretching, which is something you don't encounter on most
>> tuners but is an issue when communicating with the Xceive parts.
>>
>
> Well, the action seems to be in drivers/pci/cx23885/cx23885-i2c.c.
>
> I answer to your point above, I've had to look up what I2C clock
> stretching is and I believe that, basically, the driver would wait for
> the hardware to give the go-ahead to continue. That's what seems to be
> happening in i2c_wait_done(), but whether that's a good implementation I
> cannot say.
>
> I've noticed that there is some consistency in the failure. For example,
> if I boot the laptop, activate the dvb-t card and then run a channel
> scan, no channels will be found. If I then turn on debugging in the
> cx23885 driver (by writing 1 to
> /sys/module/cx23885/parameters/i2c_debug), and then run the scan again,
> some channels will be found. The number found varies from just a few to,
> on one occasion, all 117 of them. Then, I can turn debugging off again
> and channels will again be found when I run the scan and continue to be
> found each time I run the scan. If I reboot, the cycle starts again.
>
> I've also added some printks to the cx23885-i2c.c to find out where the
> return value of -5 (-EIO) comes from. I've found that the call to
> i2c_wait_done in i2c_sendbytes (line 145) returns 0 and that results in
> -EIO being returned a few lines later. My debug output also contained
> the value of the variable cnt, which controls the enclosing for() loop.
> cnt always has the value 3. I don't know what this might mean in terms
> of locating the problem, but hopefully someone on the list will.
>

Well, after lots of hacking diagnostics into cx23885-i2c.c, I'm pretty 
sure that this is a timing problem. I've eventually found that if I 
insert a short delay into the top of i2c_sendbytes(), my HVR-1400 
expresscard dvb-t gadget starts to work. When I run a dvb scan, it finds 
all 117 services that are found using the same device on Windows 7 (and 
by a nearby Samsung TV). I have no idea why the delay makes the card work.

A patch that makes this change is:

--- linux-3.7.6/drivers/media/pci/cx23885/cx23885-i2c.c~ 
2013-02-01 19:46:56.000000000 +0000
+++ linux-3.7.6/drivers/media/pci/cx23885/cx23885-i2c.c 2013-02-05 
14:44:47.000000000 +0000
@@ -92,6 +92,9 @@ static int i2c_sendbytes(struct i2c_adap
         else
                 dprintk(1, "%s(msg->len=%d)\n", __func__, msg->len);

+       /* The XC3028L tuner on an WinTV-HVR-1400 fails to tune without 
this */
+       udelay(8);
+
         /* Deal with i2c probe functions with zero payload */
         if (msg->len == 0) {
                 cx_write(bus->reg_addr, msg->addr << 25);

I realise it's a hack, but just in case the patch can be applied as it 
stands:

Signed-off-by: Chris Clayton <chris2553@googlemail.com>

I've found a few other things related to this driver whilst 
investigating this, but I'll report those separately.

Chris
> Chris
>> Devin
>>
>
>