On 05/03/11 20:25, Enric Balletbà i Serra wrote: > Hi guys, > I'm thinking probably in a crazy idea, I hope someone can help me or > kill definitely this idea from my mind. This is not that crazy as you think it is... > I'll explain a little more, the real problem is I don't know how to > add support for an expansion board for IGEP v2 board. I see most of > boards adds the support inside the board-xxxxx.c file, for example if > the expansion board has a Touchscreen interface using ADS7846/TSC2046 > they register ads7846 platform data in board-xxxx.c file. This is ok > beacause the ads7846 can be detected and if expansion board is not > present the detection fails, but maybe other devices in expansion > board can't be detected (for example an I/O expansion). So which is > the best form to do this ? > > I'm thinking in create a kernel module for the expansion board that > add all the new features, the expansion board should come with a I2C > E2PROM for board ID storage, so the idea is create an i2c driver that > reads the E2PROM and if found the Board ID inits all the expansion > board devices. Why do you need to create a new driver? Why don't you use the existing one? at24 works nice with most i2c EEPROMs. Let me generalize: 1) Lets call each board that actually has SoC, like IGEP, a System On Module (SoM) 2) SoM has on-board and on-SoC devices 3) expansion has additional on-board devices 4) We are talking about X SoMs and Y extensions 5) Each SoM can be connected to each extension and communicate with its devices. 6) We are looking for a solution to be able to detect the expansion and register the devices it has assembled. > I have done a few experiments, I've created a kernel module (driver) > for a custom expansion board for IGEP v2, the expansion board has : > - I2C E2PROM > - ADS7846 touch controller (spi) > - Seiko 7.0inch LCD > - General purpose I/O > > The driver is capable to register correctly i2c and spi devices and > seems is working but I have problems with the Seiko 7.0inch LCD and > configuring the MUX from driver. Like Tony already said the generic MUX API should solve the problem of MUX. But, you will still have a problem with devices that have to be initialized very early, like IO chips. > Basically I wonder if it's possible add another omap_dss_device from > kernel module to the omap DSS driver (something like > omap_dss_register_new_device). Is a good or bad idea ? Why ? Is any > reason to not export the MUX functionality to be used for other > drivers ? ... > All of this is a crazy idea ? What's the best form to solve the problem ? This is not crazy at all. We already use this concept in our BSP, we detect the expansion by reading data from EEPROM, and register the devices accordingly. We solve the MUX problem by initializing the pins to some default state and once the expansion detection is done, we reconfigure the pins to their right state as required by connected devices. And yes the above is done from board file. I don't see any reason to create a driver for the expansion, unless it can be removed/attached "on the fly" while the SoM is up and running. Nevertheless, some framework or at least an agreement on how we should separate the SoM code from the expansion code. I thought of some convention like board-*.c will stay the code for the SoM and exp-*.c will be used for the expansion code. Now, the code in board-*.c will do the detection of the expansion and run the appropriate exp_*_init() function, which will do the initialization steps for the detected expansion. A bit more complicated solution will be needed if there are several expansions connected all together. I have had this in my mind for very long time, but did not want to bother, because there were discussions about a totally different approach which uses device trees (DT), where the detection of expansion is moved away from the kernel code. With the DT approach, the kernel (should) get(s) all the information regarding the devices and how they are wired for free (no detection). If I understand correctly, the information about devices (whether on SoM or expansion) could be either statically added to the DT structures or dynamically detected by the bootloader and passed to the kernel (like ATAGS work now). I still doubt what approach would be better... -- Regards, Igor. -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
