>>-----Original Message----- >>From: Kevin Hilman [mailto:[email protected]] >>Sent: Tuesday, October 06, 2009 7:50 PM >>To: Gopinath, Thara >>Cc: Menon, Nishanth; [email protected]; Gulati, Shweta >>Subject: Re: [PATCH] OMAP3: PM: Fix for Silicon bug on Context Restore on >>OMAP3430 >> >>"Gopinath, Thara" <[email protected]> writes: >> >>>>>-----Original Message----- >>>>>From: Kevin Hilman [mailto:[email protected]] >>>>>Sent: Tuesday, October 06, 2009 6:47 PM >>>>>To: Gopinath, Thara >>>>>Cc: Menon, Nishanth; [email protected]; Gulati, Shweta >>>>>Subject: Re: [PATCH] OMAP3: PM: Fix for Silicon bug on Context Restore on >>>>>OMAP3430 >>>>> >>>>>"Gopinath, Thara" <[email protected]> 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. Regards Thara -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
