On Thu, Jan 2, 2014 at 10:27 AM, Robert Nelson <[email protected]> wrote:
> On Thu, Jan 2, 2014 at 10:11 AM, Robert Ianovich <[email protected]>
> wrote:
>> The question is why can't be accessed regularly from user space by reading
>> /dev/i2c-0 bus?
>> The I2C buses and devices can't be owned exclusively even by kernel due to
>> I2C architecture, so as far as the bus is free, anyone should read/write to
>> any address.
>>
>> I have worked on many industrial boards considerably bigger than BBB
>> (WindRiver kernel) and all devices with I2C for maintenance (RapidIO, DSP,
>> MAC/PHY, etc) are accessible.
>>
>> Why on BeagleBone the addresses of HDMI framer, PMIC and onboard EE are
>> intentionally blocked by driver ?
>> Or why the DRM driver is written that way?
>
> Well the hdmi/edid is the easly one.. As the beaglebone dose not have
> direct access to that bus, take look at page 10:
>
> https://github.com/CircuitCo/BeagleBone-Black/blob/master/BBB_SCH.pdf
>
> Thus we need to query the TDA19988 device thru drm for the edid...
>
> As far as PMIC/EE are registered by the dts in i2c0:
>
> tps: tps@24 {
> reg = <0x24>; };
>
> baseboard_eeprom: baseboard_eeprom@50 {
> compatible = "at,24c256";
> reg = <0x50>; };
>
> Thus if that blocks access thru /dev/i2c-0, i guess it blocks it...
btw the "UU" from i2cdetect in 0x24/0x50 give you a hint that the
normal i2cXYZ can't access them as they are currently busy (with the
kernel)..
root@beaglebone:~# i2cdetect -y -r 0
0 1 2 3 4 5 6 7 8 9 a b c d e f
00: -- -- -- -- -- -- -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
20: -- -- -- -- UU -- -- -- -- -- -- -- -- -- -- --
30: -- -- -- -- 34 -- -- -- -- -- -- -- -- -- -- --
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
50: UU -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
70: 70 -- -- -- -- -- -- --
(no idea where 0x34/0x70 are coming from at the moment..)
Regards,
--
Robert Nelson
http://www.rcn-ee.com/
--
For more options, visit http://beagleboard.org/discuss
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