On Sunday, December 15, 2013 at 12:51:44 AM, Sergei Ianovich wrote: > On Sat, 2013-12-14 at 18:14 +0100, Marek Vasut wrote: > > On Saturday, December 14, 2013 at 04:31:31 PM, Sergei Ianovich wrote: > > > On Sat, 2013-12-14 at 13:29 +0100, Marek Vasut wrote: > > > > Do you need to write this register in an endless loop ? > > > > > > I didn't think this way. We need to have at least 3, but up to 5 cycles > > > to put SDRAM in SLFRFRSH. It depends on the current state of SDRAM. > > > There is no way to know. > > > > OK, I seem to remember the uglinesses of the PXA DRAM controller, indeed > > :( > > > > > It can probably work if we write just once. But if we have another > > > thread doing something with SDRAM in between, we will still hang. > > > > U-Boot is single-threaded ;-) > > > > > I am not sure how likely is the situation, though. > > > > It cannot happen, really ;-) > > > > BUT (!) I understand your intention. If writing the MDREFR multiple times > > won't be a problem, I am _not_ opposed to this patch. So please only > > make sure that's not a problem and if it's not, I won't block this > > patch. > > The relevant doc is [1, section 6.1.5.4]. Refresh rules are rather > complex. However, clearing DRI and repeatedly writing to MDREFR should > refresh. The refreshes should advance SDRAM state machine to > "Self-refresh and Clock-stop". This is what we are trying to achieve. > > I've run close to 1000 reboot of patched linux kernel. This mean several > billions writes to MDREFR. If a write can cause a problem, it should > have already shown up. So I think it is not a problem.
I saw this kernel patch, yes. > Nevertheless, I've put a patched U-Boot with a single write to MDREFR to > test (reset every 2 sec). After several hours, it will be clear, if a > single write works. Let's do it the right way. Thank you ! > 1. > http://www.marvell.com/application-processors/pxa-family/assets/pxa_27x_de > v_man.pdf Best regards, Marek Vasut _______________________________________________ U-Boot mailing list U-Boot@lists.denx.de http://lists.denx.de/mailman/listinfo/u-boot
