Re: [PATCH 0/3] capebus moving omap_devices to mach-omap2
From: Cousson, Benoit
Date: Thu Nov 01 2012 - 06:23:28 EST
On 11/1/2012 8:02 AM, Pantelis Antoniou wrote:
Hi Felibe,
On Nov 1, 2012, at 12:14 AM, Felipe Balbi wrote:
Hi,
On Wed, Oct 31, 2012 at 11:36:25PM +0200, Pantelis Antoniou wrote:
* Pantelis Antoniou <panto@xxxxxxxxxxxxxxxxxxxxxxx> [121031 13:14]:
On Oct 31, 2012, at 9:55 PM, Benoit Cousson wrote:
Yeah, I do agree. I'm confused as well. Only OMAP IPs under PRCM control
could have an hwmod and thus must be handled by an omap_device.
Any devices that is created later cannot be omap_device. The DT core
will create regular platform_device for them.
Since cape is an external board, it should have nothing to do with
omap_device.
Looking at your patch:
da8xx-dt: Create da8xx DT adapter device
I understand why you do that, but in fact that patch does not make sense
to me :-(
Why do you have to create an omap_device from the driver probe?
The problem is that capes are not external boards in the normal sense
as a PCI board is. In the PCI case the hardware that implements the
desired functionality is on the PCI board, while in the cape case the
hardware module is in the SoC. The cape most of the times is quite
simple and contains passive components, leds or some kind of I2C/SPI devices.
Ah now I see, you're talking about the beaglebone extension
boards :)
The way to deal with those properly is to just edit the
board .dts entry to include omap-beaglebone-cape-xyz.dtsi
whatever.
That is what is being done...
This is the fallout.
You can't instantiate the omap_device early in the boot process like it was done up to
now in the board file. You can only do that later in the boot process (for built-in
cape drivers), or even after user-space has booted and the matching cape driver module
has been loaded.
Yes you can, just edit the .dts file for the extension
board you have connected. This stuff should be DT
only for sure, let's not even start adding platform_data
entries for that.
The omap_device entries for the omap internal devices
will be created automatically during startup based on the
.dts. Note that you can set status = "disabled" for the
omap internal devices in the .dts file, the devices are
there in the hardware.
If you are sure the extension boards are safely hot
pluggable, then all you need is some interface to enable
and disable devices after booting. But that should be
done in Linux generic way.
So we should not export any omap_hwmod or omap_device
things, and want to keep it __init only, and local to
arch/arm/mach-omap2.
I disagree. This is not something that is handled by just
editing the dts. The way it is handled, is in the Linux
generic way, we have a proper bus, and the drivers as compiled
as standalone file.
when you have an actual bus, that'd be correct.
What do you think capebus is? It is an actual bus that allows you
to do so.
We're hitting a use case that wasn't there in omap until now.
There a a whole bunch of conflicting capes. There's no
way to instantiate them together. They must be instantiated
only after their EEPROMs are read and they are matched
to their corresponding cape drivers.
why this requirement of instantiating them only after reading EEPROMs ?
It's unnecessary to add that requirement, just do what Tony said
(include my-awesome-cape.dtsi to bone.dts) and all i2c/spi devices
should be created automatically.
The thing is that there is no such thing as a cape-device. The cape is
just a collection of I2C, 1-wire and SPI devices anyway. What we should
instantiate is bmp085, tls2550, sht21, instead of instantiating
beagle-bone-weather-cape.
What's the problem in just instantiating all of those from bone.dts ?
Expose the EEPROMs to userland so whatever SW you guys have running on
the bone can figure out what features to expose to the SDK which the
user sees, but the kernel doesn't need to know that there is a
weather-cape attached to the bone.
The I2C/SPI devices are not a problem at all.
Let me try to explain what the problem is, and why it all this
is needed.
First of all, capes may be relatively simple boards, which may function
as a generic device - like the generic capes. They might not necessarily
be simple. Some capes, for example the geiger cape have a number of
components that perform a specific task; in this instance the driving
circuit of the geiger tube and the event detector input. Other capes
that are being designed now are even more complex, i.e. there's a
radar cape, an fpga cape and so on. So for these kind of boards
you will need a specific driver. That driver will probably use some
generic-cape bits (like gpios, pwms, keys what-ever).
But it will put them to use in the custom in-kernel driver in it's own
way. You can't put that task to user-space, if it's ever slightly complex.
So for really simple capes, after considerable pain you might, just
might, dump the problem to user-space and try to make it work.
People have tried that and it's a total pain. There is no way that this will
work with anything more complex than a generic cape.
Then there's the out of the box experience problem.
What a customer that buys one of these boards along with a number of
capes wants is to plug them, and have them work. You cannot have
the DTS file activating all the drivers for each possible cape since
they conflict; the pins that one SPI bus that one cape uses might be a
PWM output for another, and so on.
Asking the customer to edit the distro supplied kernel's dts and recompiling,
while figuring out how to solve conflicts is not going to fly.
Well you do not have to rebuild the kernel if you just want to update
the DTS.
The way DT is done, the best you can do is to rely on the bootloader in
your case to select the proper DTB. You should try to merge dynamically
AMxx + beaglebone + capeXXX based on some EEPROM id.
FWIW, we do have a similar, but simpler, problem with the beagle /
beagle-xm and panda / panda-es. But for the moment we are just using a
different DTS for each board.
We have the versioning problem. All the standard capes go through
a very fast evolution processes. So we now have 3 versions of a DVI cape,
2 of a small LCD cape and so on. We don't want to abandon the capes that
are already sold and are out on the field, but we don't want to spend
too much time hacking the driver to support all the different version.
The version capability of capebus handles that; taking as an example the
DVI cape in which the power down GPIO moved around:
version@00A0 {
version = "00A0";
dvi {
compatible = "da8xx-dt";
pinctrl-names = "default";
pinctrl-0 = <&bone_dvi_cape_dvi_00A0_pins>;
ti,hwmods = "lcdc";
That part is still weird to me. Assuming the lcdc is the Display
controller, the DVI should be a child of the lcdc not the opposite.
disp-pll = <560000000>;
panel-type = "1024x768@60";
powerdn-gpio = <&gpio2 7 0>;
};
};
version@00A1 {
version = "00A1", "01";
dvi {
compatible = "da8xx-dt";
pinctrl-names = "default";
pinctrl-0 = <&bone_dvi_cape_dvi_00A1_pins>;
ti,hwmods = "lcdc";
disp-pll = <560000000>;
panel-type = "1024x768@60";
powerdn-gpio = <&gpio2 31 0>;
};
};
Finally, we have the target user-base problem. The users are all going to
be hobbyists, persons that buy beaglebones as a step up from Arduino. They
will want to hack their own kind of hardware; they might not even have
an EEPROM in their custom boards. They need some kind of runtime selection
of the cape they have defined, these is handled by the case of overrides.
For example, the Adafruit 1.8 Display is pretty popular, but it's not a cape.
You have to wire it yourself and connect it to the expansion header. Then
there's two different kinds of the display. It also has a PWM input for
backlight control.
Making use of it is simple with capebus:
# cd /sys/devices/capebus.10
# echo "0:Adafruit 1.8 Cape" >slots
And that's it. The disable spi & pwm device the display needs will
be turned on, the pinmux it needs will be set, and the spi device
that the display uses will be created.
I have no clue how this can be simpler using any kind of user-space
method. And no, you can't have this active in the DTS of the common
kernel for all beaglebones.
&bone_adafruit_cape {
board-name = "Adafruit 1.8 Cape";
backlight {
compatible = "pwm-backlight";
pinctrl-names = "default";
pinctrl-0 = <&pwm_bl_pins>;
pwms = <&ehrpwm1 1 500000 0>;
pwm-names = "st7735fb";
brightness-levels = <0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36
default-brightness-level = <50>; /* index to the array above */
};
spi1-devices {
compatible = "spi-dt";
#address-cells = <1>;
#size-cells = <0>;
parent = <&spi1>;
Why do you need that? You seems to completely break the whole DT
semantic with tons of customs bindings.
From the driver code, it looks like the cape bus is not a real bus at
all. If this is just a connector, then the I2C devices will be children
of the AM33xx I2C controller, but there is no intermediate HW in the middle.
lcd@0 {
compatible = "adafruit,tft-lcd-1.8-red", "sitronix,st7735";
spi-max-frequency = <8000000>;
reg = <0>;
spi-cpol;
spi-cpha;
pinctrl-names = "default";
pinctrl-0 = <&lcd_pins>;
st7735-rst = <&gpio4 19 0>;
st7735-dc = <&gpio4 21 0>;
};
};
};
I guess there is no easy solution for that, but it looks to me that what
you have to do is to make the DT creation dynamic in your case. Assuming
you do not want to do that in the bootloader, you must do that pretty
early during the boot process to end up with a full description of your
DT tree before creating the devices.
Each cape will have their own DTS and based on some board id you will
fix the DT dynamically.
My point is that the issue you are facing is a real limitation of DT, so
you should fix the DT core and not workaround it by creating artificial
bindings / drivers.
Regards,
Benoit
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