From 4f6fc15b42776b12244af8aa28da42c8e6497742 Mon Sep 17 00:00:00 2001 From: Sekhar Nori Date: Fri, 19 Nov 2010 11:39:48 -0500 Subject: DA850 EVM: passing maximum clock rate information to kernel The TI DA850/OMAP-L138/AM18x EVM can be populated with devices having different maximum allowed CPU clock rating. The maximum clock the chip can support can only be determined from the label on the package (not software readable). Introduce a method to pass the maximum allowed clock rate information to kernel using ATAG_REVISION. The kernel uses this information to determine the maximum cpu clock rate reachable using cpufreq. Note that U-Boot itself does not set the CPU clock rate. The CPU clock is setup by a primary bootloader ("UBL"). The rate setup by UBL could be different from the maximum clock rate supported by the device. Signed-off-by: Sekhar Nori Signed-off-by: Sandeep Paulraj --- doc/README.davinci | 14 ++++++++++++++ 1 file changed, 14 insertions(+) (limited to 'doc') diff --git a/doc/README.davinci b/doc/README.davinci index a2e96a5a2..0204372a2 100644 --- a/doc/README.davinci +++ b/doc/README.davinci @@ -95,6 +95,20 @@ into the RAM. The programmers and UBL are always released as part of any standard TI software release associated with an SOC. +Environment Variables +===================== + +The DA850 EVM allows the user to specify the maximum cpu clock allowed by the +silicon, in Hz, via an environment variable "maxcpuclk". + +The maximum clock rate allowed depends on the silicon populated on the EVM. +Please make sure you understand the restrictions placed on this clock in the +device specific datasheet before setting up this variable. This information is +passed to the Linux kernel using the ATAG_REVISION atag. + +If "maxcpuclk" is not defined, the configuration CONFIG_DA850_EVM_MAX_CPU_CLK +is used to obtain this information. + Links ===== -- cgit v1.2.3