Hi Simon,
On Wed, 3 Dec 2014 19:32:18 -0700 Simon Glass sjg@chromium.org wrote:
BTW, I implemented an i2c driver for my Panasonic board base on this series, and I am playing around with it.
I found a strange behavior.
Assume an EEPROM chip is assigned with slave-address 0x50. There is no other chip on this i2c bus.
If I run "i2c probe 50" command, it correctly detects the EEPROM chip and create a generic device node "generic_50". If I run "i2c probe 49" command, it simply fails and nothing else happens.
On the other hand, when I run "i2c read 49 0.2 1 84000000", it forcibly create a generic device node "generic_49". "i2c read" command directly calls i2c_get_chip() and skips the probing step. This is odd.
My "dm tree" output is like this:
=> dm tree ROOT 9fb49028
- root_driver @ 9fb49028
`- * soc @ 9fb49098 |- * serial@54006800 @ 9fb49108, 1409312768 |- serial@54006900 @ 9fb49158, 1409313024 |- serial@54006a00 @ 9fb491a8, 1409313280 |- serial@54006b00 @ 9fb491f8, 1409313536 |- * i2c@58400000 @ 9fb49268, 0 ||- * generic_50 @ 9fb51f00 |`- * generic_49 @ 9fb51f70 <--- nothing exists on slave address 0x49 !!! |- i2c@58480000 @ 9fb492b8, 1 |- i2c@58500000 @ 9fb49308, 2 `- i2c@58580000 @ 9fb49358, 3
It should not create any device node for non-existing slave address.
I think i2c_get_chip() implementation is wrong.
My rough image of the correct implemenation is like this: The key is to split it into i2c_create_chip() and i2c_get_chip(), I think
int i2c_probe ( .... ) { i2c_probe_chip();
if (failed) return; i2c_create_chip()}
int i2c_create_chip() {
search the suitable chip driver based on DeviceTree if (found) { use it } else { call i2c_bind_driver() to create "generic" chip }}
int i2c_get_chip () { search a child node with the given chip_addr
if (found) return dev; i2c_probe();}
But that would change the bahaviour - it would then become impossible to access a chip that does not probe.
What's the problem? If it does not probe, it means no device exists on that slave address. Trying further access against non-exising device has no point.
The probe is a feature of the uclass, but it does not gate use of a device. In fact with the device tree we will typically create devices without probing them.
Precisely, devices are *bound* without probing, but should not be activated until we make sure the device really exists on the bus.
=> dm tree ROOT 9fb49028
- root_driver @ 9fb49028
`- * soc @ 9fb49098 |- * serial@54006800 @ 9fb49108, 1409312768 |- serial@54006900 @ 9fb49158, 1409313024 |- serial@54006a00 @ 9fb491a8, 1409313280 |- serial@54006b00 @ 9fb491f8, 1409313536 |- * i2c@58400000 @ 9fb49268, 0 ||- * generic_50 @ 9fb51f00 |`- * generic_49 @ 9fb51f70 <--- nothing exists on slave address 0x49 !!! |- i2c@58480000 @ 9fb492b8, 1 |- i2c@58500000 @ 9fb49308, 2 `- i2c@58580000 @ 9fb49358, 3
Here, while generic_49 does not really exist, nevertheless it is activated (has '*' mark). Very strange.
Best Regards Masahiro Yamada