PMIC device driver

Vanalme Filip F.Vanalme at
Wed Feb 16 07:20:36 EST 2011

> -----Original Message-----
> From: Vanalme Filip
> Sent: woensdag 16 februari 2011 9:38
> To: 'barebox at'
> Subject: PMIC device driver
> Up till now, I could not start up the network on my i.mx27PDK board. After
> measuring on the device, I could see that power was missing for the PHY. Good
> reason, of course, for not starting up...
> To enable the missing power, I have to adjust some registers in the PMIC device
> (mc13783).
> If I look into the mc13783.c file, I could see that this has similarities with Linux
> device drivers. So, to access the PMIC, I guess I have to do an open("/dev/pmic")
> and then a read or write. However, when I look to the pmic_read() and pmic_write()
> function, they have, besides the device pointer, buffer pointer and buffer size, an
> offset parameter that indicate the register within the PMIC to read/write. On the
> other hand, the standard read and write functions only take 3 parameters (device,
> buffer, buffersize). How do I pass that offset to these functions ? How do I use the
> PMIC device driver ?
> (Maybe this is a general Linux device driver question, but I'm not that familiar with
> device drivers, so...)
> Is it the best way to do it like this (open, read, write), or do I better call those
> functions directly ? (I have to set the PMIC registers in the "late_init" function of
> the barebox startup sequence)
> Filip Vanalme

[Filip] Think I found how it works. I have to use the normal read, write and lseek functions to read/write PMIC registers. The 'offset' and 'flag' parameters in read and write functions are for internal use only. Correct. When reading, an internal index is incremented. A following read starts where the previous ended. With lseek, one can move that index to address the correct register. Right ?

More information about the barebox mailing list