On 10/10/2013 02:13 PM, Tomi Valkeinen wrote: > On 10/10/13 14:52, Dr. H. Nikolaus Schaller wrote: > >> Yes, I agree and I am willing to help if someone comes up with such a SoC. >> At the moment we have connected it to the OMAP3 only. > > True, but even without that kind of SoC, SPI bitbanging should be > handled by an SPI driver, not by the drivers that use the bus. > >> I.e. I want not to do a lot of work for others who we just guess about that >> they >> might exist... > > Yep. It's fine for me, it's not that much extra code in the panel driver. > >>> The panel hardware has three wires, so the panel driver (if it does >>> handle the bus by bitbanging) can only refer to three gpios. >> >> Hm. The panle hardware has 3 but the SoC (OMAP3) the driver >> is running on has 4. > > Right, but this panel driver is a driver for the panel hardware. Not for > the SoC, or the SoC+panel combination. So the panel driver must only use > resources as seen by the panel hardware. > >>> So either >>> the bus details should be hidden by using the normal spi framework, or >>> if the driver does the bitbanging, use the gpios as specified in the >>> panel spec. The panel driver cannot contain any board specific stuff. >> >> The bitbang driver shown below can handle either 3 or 4 gpios (except >> for initialization). > > It's not a bitbang driver, it's a panel driver. And anyway, if I > understood right, your use of 4 gpios was just a hack to try to make it > look like a normal 4-wire SPI bus. What you really have is 3 wires, 3 > gpios. I don't see any reason to use 4 gpios, as two of them are the same. > > Hmm, how does it work anyway. Did I understand it right, the panel's > 'DIN' pin is connected to two gpios on the SoC, and one of those gpios > is set as output, and the other as input? So the SoC is always pulling > that line up or down, and the panel is also pulling it up or down when > it's sending data. I'm no HW guy but that sounds quite bad =). > > I've never written or studied a bitbanging driver, but shouldn't there > be just one gpio used on the SoC for DIN, and it would be set to either > output or input mode, depending on if we are reading or writing?
Back in the OpenMoko days we used the panel in normal 4-wire SPI mode with the GPIO bitbang SPI master. The bitbang code in this driver also looks like normal 4 wire. - Lars -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
