Russell King 7cfe249475 ARM: AMBA: Add pclk support to AMBA bus infrastructure ... Some platforms gate the pclk (APB - the bus - clock) to the peripherals for power saving, along with the functional clock. When devices are accessed without pclk enabled, the kernel will oops. This gives them two options: 1. Leave all clocks on all the time. 2. Attempt to gate pclk along with the functional clock. (With some hardware, pclk and the functional clock are gated by a single bit in a register.) (1) has the disadvantage that it causes increased power usage, which is bad news for battery operated devices. (2) can lead to kernel oops if registers are accessed without the functional clock being enabled. So, introduce the apb_pclk signal in such a way existing drivers don't need to be updated. Essentially, this means we guarantee that: 1. pclk will be enabled whenever the driver is bound to a device - from probe() to remove() time. 2. pclk will also be enabled when reading the primecell IDs from the device. In order to allow drivers to be incrementally updated to achieve greater power savings, we provide two additional calls to allow drivers to manage the pclk - amba_pclk_enable()/amba_pclk_disable(). Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>		2010-07-31 13:07:27 +01:00
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bus.c
Makefile