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authorSekhar Nori <nsekhar@ti.com>2010-11-19 11:39:48 -0500
committerSandeep Paulraj <s-paulraj@ti.com>2010-11-19 16:29:11 -0500
commit4f6fc15b42776b12244af8aa28da42c8e6497742 (patch)
treed519b49be27078d26e873d21f0015fcec982e634 /doc
parent718f746427b6eb4b9e38a9562e689a268cd65b35 (diff)
downloadu-boot-linaro-stable-4f6fc15b42776b12244af8aa28da42c8e6497742.tar.gz
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 <nsekhar@ti.com> Signed-off-by: Sandeep Paulraj <s-paulraj@ti.com>
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@@ -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
=====