Re: [PATCH 2/2] socfpga: support suspend to ram
From: atull
Date: Thu Sep 25 2014 - 13:16:43 EST
Hi Steffen,
On Thu, 25 Sep 2014, Steffen Trumtrar wrote:
> Hi!
>
> On Wed, Sep 24, 2014 at 03:27:29PM -0500, atull@xxxxxxxxxxxxxxxxxxxxx wrote:
> > From: Alan Tull <atull@xxxxxxxxxxxxxxxxxxxxx>
> >
> > Add code that requests that the sdr controller go into
> > self-refresh mode. This code is run from ocram.
> >
> > This patch assumes that u-boot has already configured sdr:
> > sdr.ctrlcfg.lowpwreq.selfrfshmask = 3
> > sdr.ctrlcfg.lowpwrtiming.clkdisablecycles = 8
> > sdr.ctrlcfg.dramtiming4.selfrfshexit = 512
> >
> > How to suspend to ram:
> > $ echo enabled > \
> > /sys/devices/soc/ffc02000.serial0/tty/ttyS0/power/wakeup
> >
> > $ echo -n mem > /sys/power/state
> >
>
> (...)
>
> Never looked into that, so maybe a stupid question:
> What happens if the bootloader (u-boot or other) didn't configure the sdr?
> Will it "just" not wake up again?
Waking up won't be the problem. Linux won't boot.
Alternatively, if this Linux kernel is paired with a version of the
bootloader that does most of the initializion, but not the settings
that we want here, I expect there could be issues.
I don't want to duplicate the u-boot sdr configuration code, instead
I document my assumptions here here. For future generations who take
this patch. If they have a problem with s2r, they will look through
the git logs and find this helpful note of what their bootloader
was supposed to do.
Alan
>
> Regards,
> Steffen
>
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