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

Signed-off-by: Sekhar Nori <nsekhar@ti.com>
Signed-off-by: Sandeep Paulraj <s-paulraj@ti.com>
Sekhar Nori 2010-11-19 11:39:48 -05:00 committed by Sandeep Paulraj
parent 718f746427
commit 4f6fc15b42
3 changed files with 48 additions and 0 deletions

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@ -118,6 +118,39 @@ static const struct lpsc_resource lpsc[] = {
#define CONFIG_DA850_EVM_MAX_CPU_CLK 300000000
* get_board_rev() - setup to pass kernel board revision information
* Returns:
* bit[0-3] Maximum cpu clock rate supported by onboard SoC
* 0000b - 300 MHz
* 0001b - 372 MHz
* 0010b - 408 MHz
* 0011b - 456 MHz
u32 get_board_rev(void)
char *s;
u32 maxcpuclk = CONFIG_DA850_EVM_MAX_CPU_CLK;
u32 rev = 0;
s = getenv("maxcpuclk");
if (s)
maxcpuclk = simple_strtoul(s, NULL, 10);
if (maxcpuclk >= 456000000)
rev = 3;
else if (maxcpuclk >= 408000000)
rev = 2;
else if (maxcpuclk >= 372000000)
rev = 1;
return rev;
int board_init(void)

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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.

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@ -140,6 +140,7 @@
"mem=32M console=ttyS2,115200n8 root=/dev/mtdblock2 rw noinitrd ip=dhcp"