On Thu, May 15, 2008 at 1:02 PM, Gary Jennejohn <[EMAIL PROTECTED]> wrote: > Hello, > > I've developed a driver for the SPI controller in the 440EPx, which should > also work for e.g. the 460EX, and maybe other AMCC processors. > > According to the UM bit 14 in SDR0_PFC1 controls whether certain signals > are for IIC1 or SPI. My driver assures that this bit is set to 0. Note > that I haven't been able to find any code in the Linux tree which > manipulates this register except for my driver, so IIC1 isn't actually > enabled for the 440EPx or the 460EX. > <snip> > > Basically I'm wondering whether anyone on this list has any brilliant > idea for handling this problem or whether my present solution is really > just OK.
Yes, this is an easy issue to solve. The way to do it is to *not* let your device drivers fiddle with board level configuration stuff (like the register that selects between SPI and I2C mode). Instead, that register should ideally setup by the bootloader, or if that is not possible, then by the platform code (the board specific stuff in arch/ppc/platforms/*). Then your driver can test that bit if it likes to see if the pins are connected; (or even better, disable the device entirely by not listing it in the device tree). In fact, if it doesn't hurt anything to have the device enabled when the bit is set against it, then the driver shouldn't care. That makes the driver more portable to other SoCs, and you should be relying on the device tree anyway to bind devices to drivers. For an example, you can look at the MPC5200 support code. There is a system level configuration register called "port_config" that controls pin routing. In most cases, u-boot sets the right value in port_config so that Linux code never needs to touch it. In cases where we cannot trust u-boot to set things up correctly, like on the lite5200 board, then the platform code fixes things up. None of the mpc5200 device drivers ever touch port_config. (See arch/powerpc/platforms/52xx/lite5200.c) Cheers, g. > > --- > Gary Jennejohn > ********************************************************************* > DENX Software Engineering GmbH, MD: Wolfgang Denk & Detlev Zundel > HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany > Phone: +49-8142-66989-0 Fax: +49-8142-66989-80 Email: [EMAIL PROTECTED] > ********************************************************************* > _______________________________________________ > Linuxppc-dev mailing list > Linuxppc-dev@ozlabs.org > https://ozlabs.org/mailman/listinfo/linuxppc-dev > -- Grant Likely, B.Sc., P.Eng. Secret Lab Technologies Ltd. _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@ozlabs.org https://ozlabs.org/mailman/listinfo/linuxppc-dev
