On 15 January 2016 at 13:43, Prashanth Prakash pprakash@codeaurora.org wrote:
cpc_read and cpc_write are used while holding the pcc_lock spin_lock, so they need to be as fast as possible. acpi_os_read/write_memory APIs linearly search through a list for cached mapping which is quite expensive. Since the PCC subspace is already mapped into virtual address space during initialization, we can just add the offset and access the necessary CPPC registers.
This patch + similar changes to PCC driver reduce the time per freq. transition from around 200us to about 20us for cppc cpufreq driver
Signed-off-by: Prashanth Prakash pprakash@codeaurora.org
drivers/acpi/cppc_acpi.c | 80 ++++++++++++++++++++++++++++++++++++++---------- 1 file changed, 64 insertions(+), 16 deletions(-)
Acked-by: Ashwin Chaugule ashwin.chaugule@linaro.org