Re: [PATCH] [media] stb0899: Fix DVB-S2 support for TechniSat SkyStar 2 HD CI USB ID 14f7:0002

[Antti Palosaari <crope@iki.fi>]

On 07.02.2014 22:54, Manu Abraham wrote:
> On Sat, Feb 8, 2014 at 1:19 AM, David Jedelsky <david.jedelsky@gmail.com> wrote:
>>> That changes I2C functionality from STOP + START to repeated START.
>>> Current functionality looks also very weird, as there is 5 messages sent,
>>> all with STOP condition. I am not surprised if actually bug is still in
>>> adapter... Somehow it should be first resolved how those messages are send,
>>> with repeated START or STOP. And fix I2C client or adapter or both.
>>>
>>> regards
>>> Antti
>>
>>
>>
>> Manu, Antti,
>>
>> Thank you for your response. I agree that the code is somewhat peculiar and
>> it could be worthy to review it using documentation before I leave it as bug
>> in my hw. Unfortunately I don't own appropriate documentation. If you can
>> supply it I can look at it.
>
> I can assure you that the STB0899 driver works well for S2 with most
> USB bridges and PCI bridges, which brings me to the fact that the issue
> does not exist with the STB0899 driver.
>
> Regarding the documentation, I don't have any wrt to the USB bridge, but
> only for the demodulator, tuner. But my hands are tied on that front, due to
> NDA's and agreements.
>
> Looking further in my hardware museum, I did find a
> Technisat Skystar USB2 HD CI REV 2.0
>
> The information on a white sticker on the PCB states:
> Model AD-SB301, Project ID: 6027
> DVB-S2, CI, USB Box (on-line update)
> H/W Ver: A1, PID/VID: 14F7 / 0002
>
> manufactured and sent to me by Azurewave.
>
> It has a broken ferrite cored inductor on it, which appears to be on the
> power line to the demodulator/tuner.
>
> The PID/VID looks exactly the same as yours. If you have a firmware bug,
> maybe it helps to update the firmware online ? (I guess the windows driver
> uses some stock Cypress driver, from what I can imagine ?)
>
> I had similar problems as you state, when I worked with a prototype version
> of the Mantis PCI chipset where it had some issues regarding repeated
> starts. I can't really remember the exact issue back then, but I do remember
> the issue being tuner related as well, since the write to the tuner would reach
> the very first tuner register alone. The communications to the tuner are
> through a repeater on the demodulator.
>
> This issue was addressed with an ECO Metal fix for the PCI bridge, but that
> did eventually result in a newer chip though.
>
> The problem could likely be similar with your USB bridge. Maybe it is a
> driver bug too .. I haven't looked deeply at the az6027 driver.

It is almost 100% sure I2C adapter or client bug. az6027 driver i2c 
adapter seems to have some weird looking things, it behaves differently 
according I2C slave address used. If I didn't read code wrong, in that 
case it does to branch "if (msg[i].addr == 0xd0)". And looking that 
logic reveals it supports only 2 I2C transfers:
for reg read: START + write + REPEATED START + read + STOP
for reg write: START + write + STOP

So that read operation (START + read + STOP) used by STB0899 is not 
implemented at all.

regards
Antti

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