Re: [PATCH] si2168: use i2c controlled mux interface

Antti Palosaari
2016-04-05T14:50:46Z

On 03/23/2016 06:58 PM, Peter Rosin wrote:
> On 2016-01-06 06:42, Antti Palosaari wrote:
>> Recent i2c mux locking update offers support for i2c controlled i2c
>> muxes. Use it and get the rid of homemade hackish i2c adapter
>> locking code.
>
> [actual patch elided]
>
> I had a 2nd look and it seems that the saa7164 driver has support for
> a HVR2055 card with dual si2168 chips. These two chips appear to sit
> on the same i2c-bus with different i2c-addresses (0x64 and 0x66) and
> with gates (implemented as muxes) to two identical tuners with the
> same i2c-address (0x60). Do I read it right?

saa7164 has 3 different I2C adapters.

saa7164 I2C bus #0:
* eeprom
* Si2157 #1

saa7164 I2C bus #1:
* Si2157 #2

saa7164 I2C bus #2:
* Si2168 #1
* Si2168 #2

So both of the Si2157 tuners could have same addresses.

(It is Hauppauge WinTV-HVR2205, not HVR-2055).

> With the current i2c-mux-locking (parent-locked muxes), this works
> fine as an access to one of the tuners locks the root i2c adapter
> and thus the other tuner is also locked out. But with the upcoming
> i2c-mux-locking for i2c-controlled muxes (self-locked muxes), the
> root i2c adapter would no longer be locked for the full transaction
> when one of the tuners is accessed. This means that accesses to the
> two tuners may interleave and cause all kinds of trouble, should
> both gates be open at the same time. So, is it really correct and
> safe to change the si2168 driver to use a self-locked mux?
>
> Unless there is some other mechanism that prevents the two tuners
> from being accessed in parallel, I think not. But maybe there is such
> a mechanism?

Good point. Actually there is pretty often this kind of configuration
used for those dual tuner devices and it will cause problems...
Currently all of those implements hackish i2c_gate_ctrl() callback to
switch mux.

____________ ____________ ____________
|I2C-adapter | | I2C-mux | | I2C-client |
|------------| |------------| |------------|
| | | addr 0x1c | | addr 0x60 |
| | | | | |
| |-+-I2C---|-----/ -----|---I2C---| |
|____________| | |____________| |____________|
| ____________ ____________
| | I2C-mux | | I2C-client |
| |------------| |------------|
| | addr 0x1d | | addr 0x60 |
| | | | |
+-I2C---|-----/ -----|---I2C---| |
|____________| |____________|

regards
Antti