Hi, Heiko: On 2016年01月05日 16:00, Heiko Stuebner wrote: > Hi Tao, > > Am Dienstag, 5. Januar 2016, 15:42:32 schrieb Huang, Tao: >> I don't think this is a good idea. This will trigger a lots of init call >> failed. Before pmic init, all i2c device driver transmit will failed, >> and because i2c is slow bus, and i2c transmit may failed by other >> reasons, so the i2c driver and i2c device driver will try many times to >> make sure the transmit completion. These unnecessary transmission will >> make Linux boot very slow. > > In general, the slowdown won't be _this_ much if touchscreen drivers need > one deferral-round before i2c is available. I'm also only pointing out > things I remember from the last time this came up. > > rk3x-i2c even was here already: > http://www.spinics.net/lists/linux-i2c/msg16680.html OK. I don't agree with the rule, but we will follow it. > > >> I2C bus should be subsys, and we can easy resolve this problem, why we >> depends on a complicated and slow implementation? > > because it's the only safe way to do that. Because now you need i2c-init at > subsys-init time, some months later some other soc may need some other > ordering, especially needing i2c-init later/earlier. > > Going through the deferral mechanism is the only way currently available to > actually make this work on all socs. > > Tomeu from Collabora is working on some better scheme to optimize device > probing order but it looks like this may be a bit off still. > > >>> Your touchscreen will have a "xyz-supply" property and I think the >>> regulator-framework should already emit a -EPROBE_DEFER at >>> regulator_get, >>> when the regulator is specified but not available yet. >> >> Unfortunately, mostly driver do not support regulator api. They are >> suppose power is on. > > Having touchscreen drivers support its proper supply-regulators is not > rocket science ;-) [0] , so I would consider this a bug in the touchscreen > driver itself. I don't just talk about touch screen driver, most i2c device driver such as input sensor/camera/rtc/battery will suffer. So people will see their drivers do not work or slow down on rk3368 platform :( Thanks! Huang, Tao -- To unsubscribe from this list: send the line "unsubscribe linux-i2c" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
