On 27 May 2011 16:31, Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx> wrote: > Hi Javier, > > 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. 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 -- Javier Martin Vista Silicon S.L. CDTUC - FASE C - Oficina S-345 Avda de los Castros s/n 39005- Santander. Cantabria. Spain +34 942 25 32 60 www.vista-silicon.com -- 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
