Hi Javier, On Friday 27 May 2011 17:36:24 javier Martin wrote: > On 27 May 2011 16:31, Laurent Pinchart wrote: > > On Thursday 26 May 2011 13:31:37 javier Martin wrote: > >> OK, I think I've found the problem with the power management. > >> > >> As it is stated in mt9p031 datasheet [3] p 59, a sequence involving > >> [VAA,VAA_PIX,VDD_PLL], [VDD,VDD_IO], [Reset] and [Ext Clk] must be > >> followed in order to properly power up or down the sensor. > >> > >> If we take a look to the LI-5M031 schematic[1] and Beagleboard xM > >> schematic [2] we'll notice that voltages are connected as follows: > >> > >> [VDD] (1,8V) <--- V2.8 <--- CAM_CORE <--- VAUX3 TPS65950 > >> [VDD_IO (VDDQ)] (1,8V) <--- V1.8 <--- CAM_IO <--- VAUX4 TPS65950 > >> [VAA, VAA_PIX, VDD_PLL] (2,8V) <---| U6 |<-- V3.3VD <-- HUB_3V3 <--| > >> U16 | enabled by USBHOST_PWR_EN <-- LEDA TPS65950 > >> > >> VAUX3 (VDD) and VAUX4 (VDD_IO) are fine, they are only used for > >> powering our camera sensor. However, when it comes to the analog part > >> (VAA, VAA_PIX...), it is got from HUB_3V3 which is also used for > >> powering USB and ethernet. > > > > *sigh* Why do hardware designers do things like that, really ? > > > >> If we really want to activate/deactivate regulators that power mt9p031 > >> we need to follow [3] p59. However, for that purpose we need to ensure > >> that a call to regulator_enable() or regulator_disable() will really > >> power on/off that supply, otherwise the sequence won't be matched and > >> the chip will have problems. > >> > >> Beagleboard xM is a good example of platform where this happens since > >> HUB_3V3 and thus (VAA, VAA_PIX, etc...) cannot be deactivated since it > >> is being used by other devices. But there could be others. > >> > >> So, as a conclusion, and in order to unblock my work, my purpose for > >> power management in mt9p031 would be the following: > >> - Drop regulator handling as we cannot guarantee that power on > >> sequence will be accomplished. > >> - Keep on asserting/de-asserting reset which saves a lot of power. > >> - Also activate/deactivate clock when necessary to save some power. > >> > >> I'm looking forward to read your comments on this. > > > > Even if you keep the sensor powered all the time, how do you ensure that > > VAUX3 is available before HUB_3V3 when the system is powered up ? > > You can't. And in fact what happens its the opposite. But it works. I wonder why, as the power supplies are sequenced the wrong way. It seems like the hardware has been designed not to work. Sometimes I wish hardware designers would read the chip specs before shipping boards in the wild and relying on us to fix their mistakes. > On the other hand, not being able to disable/enable HUB_3V3 can make, > as a hardware guy has told me, power on reset internal circuit not to > work [1] and thus the power down / power up fails. > > [1] http://en.wikipedia.org/wiki/Power-on_reset -- Regards, Laurent Pinchart -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
