On 2/15/2012 1:01 PM, Archit Taneja wrote:
On Tuesday 14 February 2012 09:11 PM, Cousson, Benoit wrote:
On 2/14/2012 2:30 PM, Archit Taneja wrote:
Hi,
On Tuesday 14 February 2012 06:45 PM, Tomi Valkeinen wrote:
On Tue, 2012-02-14 at 13:58 +0100, Cousson, Benoit wrote:
Hi Tomi,
Benoit, do you think we'll get the MODULEMODE mess cleaned up in the
hwmod/clk framework at some point, and the drivers could do without
these kinds of hacks? =)
The best way to fix that for my point of view is to go to device tree
or/and to consider the DSS as the parent of all the DSS modules.
pm_runtime will then always ensure that the parent is enabled before
any
of the child are used.
Ah, right. Sounds fine to me.
But is that a proper "fix"? Are we sure the MODULEMODE will then always
be handled correctly? Isn't the core problem still there, it just
doesn't happen with the setup anymore?
I mean, if we have these special requirements regarding MODULEMODE, and
the code doesn't really know about it, would it get broken easily with
restructuring/changes?
And no, I don't have any clear idea why/how it would break, but I have
just gotten the impression that the MODULEMODE is not handled quite
properly (and so we have these current problems), and having
dss_core as
the parent of other dss modules doesn't really fix that in any way.
I agree with that.
In the current approach, we have multiple platform devices for DSS, and
all of them belong to the same clock domain, and the clock domain has
just one MODULEMODE bit field.
When shutting off a platform device(by calling pm_runtime_put()), hwmod
enables/disables MODULEMODE without taking into mind that other active
platform devices may still need it. So, for example, if we have 2
platform devices, say dss and dispc, and we have code like:
dispc_foo()
{
pm_runtime_get(dispc_pdev);
...
...
pm_runtime_put(dispc_pdev);
}
dss_foo()
{
pm_runtime_get(dss_pdev);
...
...
dispc_foo(); /* MODULEMODE off after this */
...
...
pm_runtime_put(dss_pdev);
}
This will lead to the situation of one platform device disabling
MODULEMODE even though other platform devices need it.
This may not be resolved in device tree either. We would need to have
some use count mechanism for these bits, or attach MODULEMODE only to
one platform device, and don't give others control to enable/disable it.
And this is exactly what the pm_runtime will provide. The fmwk already
handles reference counting.
Moreover the dev->parent will increment the power.child_count and thus
ensure that the parent is always enabled if at least one child is active.
By initializing the dev->parent of each DSS modules to the dss_core, it
will ensure that the power dependency is managed properly.
Yes, a parent/child relation will ensure the required dependencies. It
sounds good!
How do we take care of things in the meanwhile? With the current way of
representing modulemode as a slave clock, the disabling sequence gets
messed up. In arch/arm/mach-omap2/omap_hwmod.c:
static int _disable_clocks(struct omap_hwmod *oh)
{
...
disable mainclk;
disable slave clocks;
...
}
For DSS, mainclk is the DSS_FCLK opt clock, and slave clock is
modulemode bits. We need the opposite sequence to happen here to cleanly
disable DSS.
Yes, but as you pointed out the current clocks mapping in the DSS is a
hack that should not be done like that in theory.
As soon as the devices can handle the dependency, we will be able to fix
the clock mapping in the hwmod data and handle properly the module mode
only from the dss_core hwmod only.
But I think you have to change the driver first, otherwise it will break
the DSS. We did that hack previously because it was the only way to
enable the DSS properly, knowing that disabling it with that method will
be impossible.
I think that changing the device creation to change the dev->parent
should be pretty straightforward.
Regards,
Benoit
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