From: "Frank Schäfer" <fschaefer.oss@googlemail.com>
To: Antti Palosaari <crope@iki.fi>
Cc: linux-media@vger.kernel.org
Subject: Re: Mysterious USB device ID change on Hauppauge HVR-900 (em28xx)
Date: Fri, 23 Nov 2012 20:24:21 +0100 [thread overview]
Message-ID: <50AFCD65.90200@googlemail.com> (raw)
In-Reply-To: <50AFB05B.6020209@iki.fi>
Am 23.11.2012 18:20, schrieb Antti Palosaari:
> On 11/23/2012 07:01 PM, Frank Schäfer wrote:
>> Hi,
>>
>> I've got a Hauppauge HVR-900 (65008/A1C0) today. First, the device
>> showed up as USB device 7640:edc1 (even after several unplug - replug
>> cycles), so I decided to add this VID:PID to the em28xx driver to see
>> what happens.
>> That worked fine, em2882/em2883, tuner xc2028/3028 etc. were detected
>> properly.
>> Later I noticed, that the device now shows up as 2040:6500, which is the
>> expected ID for this device.
>> Since then, the device maintains this ID. I also checked if Windows is
>> involved, but it shows up with the same ID there.
>>
>> Does anyone have an idea what could have happened ???
>> I wonder if we should add this ID to the em28xx driver...
>
> em28xx chip reads USB ID from the external eeprom using I2C just after
> it was powered. After USB ID is got it connects to the USB bus using
> that ID. If there is no external eeprom it uses chipset default USB
> ID, which is 0xeb1a as vendor ID and some other number defined for
> chip model as device ID. In that case those wrong IDs seems to be
> total garbage, which indicates there is some hardware problems when
> communicating towards eeprom.
>
Yeah, hardware problems, sure... but I wonder why the USB ID was/is
persistent ? Communication problems caused by circuit defect should lead
to a rather random behavior...
On power loss, the everything except (ee)prom(s) contents should be
reset to a default state.
And if the eeprom was corrupted, how could it magically recover ?
Also: the USB id is read from the eeprom even without a OS driver beeing
involved, but the first usage of the driver seems to have "fixed" the ID...
Regards,
Frank
> That method is not only Empia USB interface chips but almost all
> chipset uses just similar method.
>
>
> regard
> Antti
>
next prev parent reply other threads:[~2012-11-23 19:24 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-11-23 17:01 Mysterious USB device ID change on Hauppauge HVR-900 (em28xx) Frank Schäfer
2012-11-23 17:20 ` Antti Palosaari
2012-11-23 19:24 ` Frank Schäfer [this message]
2012-11-23 20:10 ` Mauro Carvalho Chehab
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