I2C adaption layer driver for libbsd (was: Re: rtems-libbsd build error)

Vijay Kumar Banerjee vijaykumar9597 at gmail.com
Thu Apr 18 19:11:13 UTC 2019


On Thu, Apr 18, 2019 at 12:39 AM Christian Mauderer <list at c-mauderer.de>
wrote:

> First: Please note that I changed the toppic. The old one just didn't
> represent the content any more.
>
> Am 17.04.19 um 20:40 schrieb Vijay Kumar Banerjee:
> [...]
> >     >     >
> >     >     >     Am 09.04.19 um 18:12 schrieb Vijay Kumar Banerjee:
> >     >     >     > Hi,
> >     >     >     >
> >     >     >     > I have imported and ported the the drivers in 2
> >     pairs(import
> >     >     and port)
> >     >     >     > of commits
> >     >     >     > for each one. Please have a look at this branch
> >     >     >     >
> >     https://github.com/thelunatic/rtems-libbsd/commits/tda19988
> >     >     >
> >     >     >     One detail: You have a commit named "tda19988.c: import
> from
> >     >     FreeBSD".
> >     >     >     Please remove the ".c".
> >     >     >
> >     >     > Noted.
> >     >     >
> >     >     >     Maybe it would be a good idea to split of the I2C part
> >     and put
> >     >     it in
> >     >     >     front of the other two parts. You can develop and test
> that
> >     >     independent
> >     >     >     with a test that just accesses some of the I2C devices
> >     on the
> >     >     board via
> >     >     >     the FreeBSD API and the translation driver discussed
> below.
> >     >     >
> >     >     > This is a good idea, I'll import iicbus separately and add
> >     the other
> >     >     > two on top of it.
> >     >     >
> >     >     >     >
> >     >     >     > I have also tried running the media01.exe and have
> seen it
> >     >     running
> >     >     >     fine
> >     >     >     > without
> >     >     >     > throwing any exceptions.
> >     >     >     >
> >     >     >     > I have used the fb.c and iicbus.c codes from the
> >     >     freebsd source. From
> >     >     >     > what I
> >     >     >     > understand, I think the next big steps would be to
> >     write an
> >     >     RTEMS
> >     >     >     > implementation layer for these portions of the code?
> >     And then a
> >     >     >     test in the
> >     >     >     > libbsd, like media01, to write to the /dev/fb0
> >     >     >     >
> >     >     >     > Can you please help me chalk out a rough outline of
> >     the next
> >     >     set of
> >     >     >     > actions? :)
> >     >     >
> >     >     >     As far as I can tell, there are two possible I2C buses
> here:
> >     >     >
> >     >     >     1. The one between the AM335x and the TDA19988.
> >     >     >
> >     >     >     2. The one directly on the HDMI connector (called
> >     HDMI_DSCL and
> >     >     >     HDMI_DSDA). I assume that's an I2C bus too.
> >     >     >
> >     >     >     For 1. the RTEMS driver should be used. You'll need some
> >     code that
> >     >     >     translates the FreeBSD API to the one used in RTEMS.
> >     Basically
> >     >     that will
> >     >     >     just be a FreeBSD-I2C-driver.
> >     >     >
> >     >     >     For 2: If that even is an independent I2C bus, you can
> >     use the
> >     >     driver
> >     >     >     provided by FreeBSD. I don't think that it is necessary
> to
> >     >     translate to
> >     >     >     the RTEMS API here.
> >     >     >
> >     >     > I had a look at the iic and iicbus codes in freebsd and the
> >     bbb-i2c.c
> >     >     > This looks very confusing to me. Are we looking for
> >     something like a
> >     >     > rtems-iicbus.c in the rtemsbsd that works like a wrapper to
> the
> >     >     bbb-i2c
> >     >     > code, and uses the freebsd api of DEVMETHODs?
> >     >
> >     >     Yes correct. Basically it would be necessary to have a I2C
> >     device driver
> >     >     for FreeBSD that translates to the RTEMS API.
> >     >
> >     >     >
> >     >     > I've not been able to figure out at one look, how to relate
> >     them and
> >     >     > get a wrapper like that. Any suggestions on how to approach
> >     this?
> >     >
> >     >     I haven't had a look at the FreeBSD drivers yet. The first
> >     part that I
> >     >     would have a look at is the description of the user facing
> >     FreeBSD API:
> >     >
> >     >
> >
> https://www.freebsd.org/cgi/man.cgi?query=iic&apropos=0&sektion=0&manpath=FreeBSD+12.0-RELEASE+and+Ports&arch=default&format=html
> >     >
> >     >     Nice thing: They use a struct iic_msg that is compatible with
> >     Linux's
> >     >     struct i2c_msg (according to the man page). We are Linux
> >     compatible too.
> >     >     Can be a big advantage.
> >     >
> >     >     Then take a look at the simplest i2c driver that you can find
> >     in FreeBSD
> >     >     that uses the transfer API.
> >     >     freebsd-org/sys/dev/drm2/radeon/atombios_i2c.c looks good to
> me.
> >     >     Basically you have to implement the following functions
> (replace
> >     >     radeon_atom... by a useful prefix):
> >     >
> >     >     static device_method_t radeon_atom_hw_i2c_methods[] = {
> >     >             DEVMETHOD(device_probe,
>  radeon_atom_hw_i2c_probe),
> >     >             DEVMETHOD(device_attach,
> >     radeon_atom_hw_i2c_attach),
> >     >             DEVMETHOD(device_detach,
> >     radeon_atom_hw_i2c_detach),
> >     >             DEVMETHOD(iicbus_reset,
>  radeon_atom_hw_i2c_reset),
> >     >             DEVMETHOD(iicbus_transfer,
> radeon_atom_hw_i2c_xfer),
> >     >             DEVMETHOD_END
> >     >     };
> >     >
> >     >     The iicbus_transfer function seems to get a struct iic_msg as a
> >     >     parameter. Now that's really lucky.
> >     >
> >     >     With that you should be able to open the i2c device in RTEMS
> >     and just
> >     >     pass the structure via the correct ioctl call to the RTEMS
> driver.
> >     >
> >     >     Basically you just have to pass the bus to use as a parameter
> >     to the
> >     >     driver. Take a look at some of the other drivers in
> >     nexus-devices.h that
> >     >     have for example an address as a parameter to see how you can
> >     do that.
> >     >
> >     > This gave a good idea of the objective. :)
> >     >
> >     > I had a look at the  bbb-i2c.c code and how it's registering
> >     > and setting up the i2c_bus struct with the transfer, set and
> destroy
> >     > fucntions.
> >     > I have a question from the fundamentals, the only function
> >     > of bbb-i2c.c
> >     > <
> https://git.rtems.org/rtems/tree/bsps/arm/beagle/i2c/bbb-i2c.c#n414>
> >     > that is 'accessible' with the header file is
> am335x_i2c_bus_register
> >     > which basically sets the i2c_bus struct
> >     > and calls the i2c_bus_register function from the dev/i2c.c .
> >     > To use the DEVMETHOD api, we need to be able to call the
> >     > transfer, destroy etc. functions of the bbb-i2c.c from the
> translation
> >     > layer in rtemsbsd. How do I #include the bbb-i2c.c in the new
> >     > translation driver that I'll write?
> >     >
> >     > Hope my question is stated clearly, please correct me if I'm
> getting
> >     > some fundamentals wrong.
> >
> >     You are not fundamentally wrong but slightly off:
> >
> >     Regarding the question how you access transfer, destroy, ... of the
> >     driver directly: Don't.
> >
> >     You basically don't need to have a look at the bbb-i2c.c file of
> RTEMS
> >     for that driver. Where you should have a look is the Linux I2C API
> >     (which has been the model for the RTEMS API).
> >
> >     Basically your drivers transfer function will do about the following:
> >
> >     - Open "/dev/i2c0" (or some other path - that will be a parameter to
> the
> >     driver and has to be stored by probe or attach in some device
> >     structure).
> >
> >     - Translate the "struct iic_msg" you get as an input to a "struct
> >     i2c_msg". Most likely that's just a cast.
> >
> >     - Pass that via an ioctl call to the opened bus.
> >
> >     - Check return value and translate to the matching return of FreeBSD.
> >
> >     - Close "/dev/i2c0"
> >
> >     Some of the open / close might could move to attach / detach. But
> that
> >     would be an optimization.
> >
> >     That driver will work on any BSP that implements the current i2c
> API. So
> >     it's a generic translation layer.
> >
> >     Best regards
> >
> >     Christian
> >
> > Hi!
> >
> > I started writing the driver layer implementation in the rtemsbsd, is
> > this going in the right
> > direction
> > <https://gist.github.com/thelunatic/2d8a2bf2cbead5bf82abe09000afea56> ?
>
> Yes. That's the direction I had in mind.
>
> Regarding that part:
>
>     //XXX: Open /dev/iic0
>     strcpy(addr, "/dev/");
>     strcat(addr, device_get_nameunit(dev));
>
> Sooner or later that should be received via a parameter. I just had a
> look at nexus-devices.h: It seems that there is currently only support
> for two kinds of "parameters": memory resources and interrupts.
>
> What would be necessary would be more of a string parameter like they
> are available via the device tree interface. This kind of parameters is
> normally retrieved in the driver with the OF_getprop_alloc() function.
>
> Problem is: The driver you currently write isn't one that is normally
> put into a device tree file. So some other source for the string
> parameter is necessary. I'll have to have a more detailed look at how
> the parameter could get into the driver in the next few days.
>
> I would suggest to start with a fixed string for now. Assume that it
> will somehow appear in the attach function (that would be the location
> where such parameters would be parsed most of the time).
>
> Hi,
I have updated the gist a bit, to use a macro for the path for now, and
also added
the probe and destroy function. This looks like a better outline now, I
haven't written
the attach function, you can have a detailed look at it and suggest ways to
parse the
path in the attach.

> >
> >
> >     >
> >     >     >
> >     >     > Can we not totally use the iicbus in the freebsd source?
> >     >
> >     >     We already have a I2C driver for that BSP in RTEMS. If you
> >     would use the
> >     >     FreeBSD code, they would fight for the hardware. Of course it
> >     would be
> >     >     possible to replace the RTEMS driver by a FreeBSD one. But
> >     that would
> >     >     potentially break some applications. Besides that I think that
> >     a lot of
> >     >     RTEMS BSPs already have an I2C driver so a generic wrapper
> >     could be
> >     >     helpful for other BSPs too.
> >     >
> >     >     >
> >     >     >     >
> >     >     >     > Thanks
> >     >     >     >
> [...]
>
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