In the coresight CPU debug document it suggests to use 'echo' command
to set latency request to /dev/cpu_dma_latency so can disable all CPU
idle states, but in fact this doesn't work.
This is because when the command 'echo' exits, it releases the device
node's file descriptor and the kernel release function removes the QoS
constraint; finally when the command 'echo' finished there have no
constraint imposed on cpu_dma_latency.
This patch changes to use 'exec' to access '/dev/cpu_dma_latency', the
command 'exec' can avoid the file descriptor to be closed so we can
keep the constraint on cpu_dma_latency.
This patch also adds the info for reference docs for PM QoS and cpuidle
sysfs.
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Sudeep Holla <sudeep.holla@arm.com>
Reported-by: Kim Phillips <kim.phillips@arm.com>
Suggested-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Signed-off-by: Leo Yan <leo.yan@linaro.org>
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Add detailed documentation for Coresight CPU debug driver, which
contains the info for driver implementation, Mike Leach excellent
summary for "clock and power domain". At the end some examples on how
to enable the debugging functionality are provided.
Suggested-by: Mike Leach <mike.leach@linaro.org>
Signed-off-by: Leo Yan <leo.yan@linaro.org>
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
