On Mon, 2012-06-25 at 17:57 +0530, Jassi Brar wrote: > On 25 June 2012 15:00, Tomi Valkeinen <tomi.valkeinen@xxxxxx> wrote: > > The driver needs to enable the HW and the call to pm_runtime_get() is > > skipped. Won't this lead to crash as the DSS registers are accessed > > without the HW in enabled state? > > > Hmm... how does the extant code in hdmi driver ensures DSS is up and running ? > While it does sound important even to my limited knowledge of OMAPDSS, > I see rpm of HDMI, VENC and RFBI only dependent on DISPC, not DSS. DSS device is parent to all the DSS subdevices. So when a subdevice is enabled, DSS device is enabled first. But anyway, I wasn't referring to the DSS part of OMAPDSS, but to omapdss generally. If we do this: /* this is skipped, if runtime PM is disabled */ dispc_runtime_get(); /* this accesses a register, but the HW is disabled? */ dispc_read_reg(FOO); So again, I don't understand how the underlying HW gets enabled. Or does hwmod/omap_device code make sure that it's enabled while the board is being resumed? If so, what would happen if we continue the above scenario as follows: /* this is skipped, if runtime PM is disabled */ dispc_runtime_get(); /* this accesses a register, the HW is kept enabled by hwmod */ dispc_read_reg(FOO); /* at some time later the resume procedure ends, and hwmod doesn't keep the HW enabled any more */ /* this accesses a register, the HW is disabled */ dispc_read_reg(FOO); > And for DISPC these drivers already hold a reference in their display > enable/resume and keep it until disable/suspend. So we don't lose > DISPC anytime it is really required. If all the displays are disabled, nobody keeps a reference to dispc. > > And what happens if the pm_runtime_get() call is skipped, but pm_runtime_put() is not? > > > Not sure in what newly introduced scenario by this patch, because > get/put both check for pm_enabled before proceeding. Am I overlooking > something? Currently (for example) dispc_runtime_get/put call pm_runtime_get/put_sync. When somebody uses dispc_runtime_get, the same somebody knows it needs to call dispc_runtime_put later. Now, what happens if dispc_runtime_get is called when runtime PM is disabled (i.e. pm_runtime_get_sync is skipped), but runtime PM is enabled later when that somebody calls dispc_runtime_put (i.e. pm_runtime_put_sync is _not_ skipped)? Tomi
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