On 8/21/08, David Miller <davem@xxxxxxxxxxxxx> wrote: > > I'm working on some drivers for I2C bus support on some of my sparc64 > workstations (for lm-sensor and eeprom type devices sitting behind > them) so I went back to trying to get of_i2c.c usable on sparc. > > Mostly straightforward stuff _except_ for the I2C address encoding. > > What I2C IEEE1275 device binding was used to write that code in > of_i2c.c? Is it some PowerPC specific thing? Was it "invented" > by the embedded folks (I hope not)? > > On sparc, the encoding is either 1 cell or 2 cell. > > If it's one cell, it's just the device address. > > If it's two cells, it's a bus number (for I2C controllers that > can manage multiple I2C bus segments, think PCI domains) in the > first cell and the device address in the second cell. > > And, furthermore, the device address is shifted up 1 bit higher > than the Linux I2C layer expects. It includes the low direction > bit, bit 0, so we have to shift it down by 1 bit before we give > it to the Linux I2C layer. > > Does PowerPC really encode these things differently? And if so what > IEEE1275 I2C device binding specification covers that? > > If PowerPC really does encode the device address in the same format as > the Linux I2C layer expects, that's OK and I used some property tests > and ifdefs to make it all work out. What I did in these patches is: > > 1) Check the #address-cells property. If not present, assume the value > is "1". Only accept values of "1" and "2". > > 2) When CONFIG_SPARC, shift the device address down by one bit before > giving it to the Linux I2C layer. How do you deal with a 10-bit address i2c device? Is it multiplied by two too? Here's the i2c spec, http://www.semiconductors.philips.com/acrobat_download/literature/9398/39340011.pdf It says the basic addresses are 7 bit. > I haven't added support to the I2C layer for the bus number yet, that > will come later. > > The first patch in this series add the powerpc-compat IRQ probing > interfaces, mostly straightforward stuff as we precompute these > IRQs in of_device objects so we just search for the of_device corresponding > to the device node and return the interrupt, if any. Dispost is a NOP. > > The second patch deals with the addressing issues described above and > lets it be compiled on non-ppc systems. > > The third patch adds device modaliases for a couple of I2C chip devices > I've seen on my SunBlade2500 workstation. More will come later as I > flesh out my I2C sparc64 drivers which are not being posted here yet. > I have a fully functional Sun pcf8584 I2C bus driver. > > Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx> > -- Jon Smirl jonsmirl@xxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe sparclinux" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
