Hi Kevin,
On Thursday 11 April 2013 07:45 PM, Kevin Hilman wrote:
Kevin Hilman<khilman@xxxxxxxxxx> writes:
"Bedia, Vaibhav"<vaibhav.bedia@xxxxxx> writes:
Hi Sourav,
On Wed, Apr 10, 2013 at 15:13:44, Poddar, Sourav wrote:
[...]
Yes, had a look at that and found your situation similar to UART.
But how exactly this gets used, I mean I don't see any drivers/ in mainline
making use of this compatible string "ti,am3352-ocmcram". ?
OCMC clock is enabled during bootup (not sure whether that's the h/w
default or ROM does it) since the initial bootloader runs from there.
By marking the corresponding hwmod with HWMOD_INIT_NO_IDLE we leave the
clock running. Right now the sram code under arch/arm/plat-omap/ is what
manages the OCMC. I guess this needs to move somewhere under drivers/
and start managing the clocks. Even then we'll need a mechanism
to leave the clocks running as part of the kernel suspend process
since the assembly code which runs at the fag end of the suspend
process runs out of OCMC and hence we can't cut its clock.
On AM335x, the OCMC clock is cut to have PER power domain transition
but that's done in the WKUP-M3 firmware when going down. During the
wakeup sequence, WKUP-M3 re-enables the OCMC clock so that when the
kernel resumes the h/w state is same.
OK, but *today*, in *mainline*, where in the linux kernel (not the M3
firmware) is the OCMRAM clock cut during suspend?
From what I can see, there is no driver for this device, so there are no
system PM calls being done for that device, and thus no omap_device
calls being done for that device, so the no_idle_on_suspend has no
effect.
OK, I think I confused things here, sorry. I was thinking runtime PM
here, but wrote system PM. The no_idle_on_suspend feature only affects
system PM, and the omap_device calls will still be called during system
PM, even without a driver.
That being said, the commit below[1], added in v3.6 should prevent the
any automaic clock gating for devices without drivers bound. Since
there is no driver for the OCM RAM block, you shouldn't be affected by
the automatic idle on suspend anyways.
So, my proposal is that Sourav remove that flag from the AM33xx hwmod
when he removes this feature.
Kevin
Thanks a lot for your inputs and helping in bringing this thread to
a logical conclusion.
I will post a v4 for this patch along with other fixes/cleanups
required as recommended by you and russell.
Thanks,
Sourav
[1]
commit 72bb6f9b51c82c820ddef892455a85b115460904
Author: Kevin Hilman<khilman@xxxxxx>
Date: Tue Jul 10 15:29:04 2012 -0700
ARM: OMAP: omap_device: don't attempt late suspend if no driver bound
Currently, the omap_device PM domain layer uses the late suspend and
early resume callbacks to ensure devices are in their low power
states.
However, this is attempted even in cases where a driver probe has
failed. If a driver's ->probe() method fails, the driver is likely in
a state where it is not expecting its runtime PM callbacks to be
called, yet currently the omap_device PM domain code attempts to call
the drivers callbacks.
To fix, use the omap_device driver_status field to check whether a
driver is bound to the omap_device before attempting to trigger driver
callbacks.
Reviewed-by: Paul Walmsley<paul@xxxxxxxxx>
Signed-off-by: Kevin Hilman<khilman@xxxxxx>
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