"Gopinath, Thara" <thara@xxxxxx> writes: >>>-----Original Message----- >>>From: Kevin Hilman [mailto:khilman@xxxxxxxxxxxxxxxxxxx] >>>Sent: Tuesday, October 06, 2009 7:50 PM >>>To: Gopinath, Thara >>>Cc: Menon, Nishanth; linux-omap@xxxxxxxxxxxxxxx; Gulati, Shweta >>>Subject: Re: [PATCH] OMAP3: PM: Fix for Silicon bug on Context Restore on OMAP3430 >>> >>>"Gopinath, Thara" <thara@xxxxxx> writes: >>> >>>>>>-----Original Message----- >>>>>>From: Kevin Hilman [mailto:khilman@xxxxxxxxxxxxxxxxxxx] >>>>>>Sent: Tuesday, October 06, 2009 6:47 PM >>>>>>To: Gopinath, Thara >>>>>>Cc: Menon, Nishanth; linux-omap@xxxxxxxxxxxxxxx; Gulati, Shweta >>>>>>Subject: Re: [PATCH] OMAP3: PM: Fix for Silicon bug on Context Restore on OMAP3430 >>>>>> >>>>>>"Gopinath, Thara" <thara@xxxxxx> writes: >>>>>> >>>>>>> The problem here is not with the restore. If MPU reads the PADCONF_SAVEDONE bit very close >>>>>>> to the end of context save sequence for the pad conf registers, the last context is not >>>>>>> saved to the scratchpad memory. This is a h/w bug. The workaround proposed is to delay the >>>>>>> MPU access of SAVEDONE bit until the last context has been saved. 300 us delay is the current >>>>>>> safe delay proposed by TI. I believe investigations are going on to whether this delay can be >>>>>>> optimized. Also only the last context (ETK_D14) has the risk of not getting saved. >>>>>> >>>>>>All of this should've been in the original changelog. These are the >>>>>>details that help others understand the problem trying to be solved >>>>>>and think about whether there might be other solutions. >>>>>> >>>>>>> We could add a defconfig option for this workaround and enable it on need basis till TI >>>>>>> comes out with proper optimized workaround sequence. >>>>>> >>>>>>No, Kconfig is not an option for this. >>>>>> >>>>>>I think Nishanth's proposal is a much better workaround for this >>>>>>problem, and doesn't introduce and additional 300 usec delay to >>>>>>*every* off-mode transistion. >>>> >>>> I am not very sure about this as it has the risk of glitch on the >>>> line. It is probably ok if the ball is not used. But if in use, the >>>> glitch could create issues. >>> >>>I don't follow. >>> >>>IIUC, Nishanth's proposal would be to >>> >>>In save context: >>>- manually save ETK_D14 to some static variable (SDRAM) >>>- initiate the padconf safe >>>- poll SAVE_DONE >>>- here ETK_D14 value saved by HW possibly corrupted, >>> but the copy saved manually should be fine >>> >>>In restore: >>>- manually restore ETK_D14 from the static variable >>> >>>What is wrong with this approach? > In this approach there is a possibility that the h/w restore a wrong value to PADCONF_ETKD14. > Now suppose this pin is in use and is supposed to be pulled high. And the proper save does not happen > 1. Before going to Off - the pin is pulled high > 2. Off > 3. h/w restore - Has done bad save. So bad value restored. Say pull low. > 4. Manual restore - the pin is again pulled high. > > Now there is a glitch between step 3 and 4. If this pin is not used by anybody we could live with this glitch. But considering this pin is muxed with gpio28/gpio29, hsusb_tll_data0/ hsusb_tll_data1 this glitch might be unacceptable. I see now. Thanks for explanation. Kevin -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
