From: Jon Hunter Date: Fri, 23 Aug 2013 10:40:23 +0000 (-0600) Subject: ARM: OMAP2+: Only write the sysconfig on idle when necessary X-Git-Tag: sz_161~51 X-Git-Url: https://git.openpandora.org/cgi-bin/gitweb.cgi?p=pandora-kernel.git;a=commitdiff_plain;h=e7accd0b0918c99c705c5f6774e72f076cffc14f ARM: OMAP2+: Only write the sysconfig on idle when necessary Currently, whenever we idle a device _idle_sysc() is called and writes to the devices SYSCONFIG register to set the idle mode. A lot devices are using the smart-idle mode and so the write to the SYSCONFIG register is programming the same value that is already stored in the register. Writes to the devices SYSCONFIG register can be slow, for example, writing to the DMTIMER SYSCONFIG register takes 3 interface clock cycles and 3 functional clock cycles. If the DMTIMER is using the slow 32kHz functional clock this can take ~100us. Furthermore, during boot on an OMAP4430 panda board, I see that there are 100 calls to _idle_sysc(), however, only 3 out of the 100 calls actually write the SYSCONFIG register with a new value. Therefore, to avoid unnecessary writes to device SYSCONFIG registers when idling the device, only write the value if the value has changed. It should be safe to do this on idle as the context of the register will never be lost while the device is active. Verified that suspend, CORE off and retention states are working with this change on OMAP3430 Beagle board. Signed-off-by: Jon Hunter [paul@pwsan.com: updated to apply] Signed-off-by: Paul Walmsley --- diff --git a/arch/arm/mach-omap2/omap_hwmod.c b/arch/arm/mach-omap2/omap_hwmod.c index b4f31c34f02b..5ccbd709fc54 100644 --- a/arch/arm/mach-omap2/omap_hwmod.c +++ b/arch/arm/mach-omap2/omap_hwmod.c @@ -981,7 +981,9 @@ static void _enable_sysc(struct omap_hwmod *oh) (sf & SYSC_HAS_CLOCKACTIVITY)) _set_clockactivity(oh, oh->class->sysc->clockact, &v); - _write_sysconfig(v, oh); + /* If the cached value is the same as the new value, skip the write */ + if (oh->_sysc_cache != v) + _write_sysconfig(v, oh); /* * Set the autoidle bit only after setting the smartidle bit