Allocating boot time memory using dts configuration - memory

Question

I am working with a particular encoder which uses 512M boot time allocated memory. I am supposed to allocate the memory through dts file configuration. The physical memory is devided into low and high as below in the dts file:
/* 256MB at 0x0 */
memory#0 {
device_type = "memory";
reg = <0x0 0x00000000 0x0 0x10000000>;
};
/* 2GB at 0x8010000000 */
memory#8000000000 {
device_type = "memory";
reg = <0x80 0x10000000 0x0 0x80000000>;
};
Now I want to allocate the boot time carved out memory from the high memory. I can think of creating a dts entry as below
encoder: encoder#0xxxxxxxxx {
compatible = "xyz, abc";
reg= <0x0 0x80000000 0x0 0x20000000>;
}
Here the encoder#xxxx is the actual device entry and it has already a set of register region as below:
encoder: encoder#0xxxxxxxxx{
compatible = "xyz, abc";
#address-cells = <1>;
#size-cells = <1>;
reg = <0x0 0xxxxxxxxxx 0x0 0x1234>;
status = "disabled";
};
So after adding the carvedout memory the entry would look like this:
encoder: encoder#0xxxxxxxxx{
compatible = "xyz, abc";
#address-cells = <1>;
#size-cells = <1>;
reg = <0x0 0xxxxxxxxxx 0x0 0x1234>;
reg= <0x0 0x80000000 0x0 0x20000000>;
status = "disabled";
};
Would this work? I am not sure though how the driver code would know where is the start address of the carved out memory and the size of it?
Can anyone please help?
Thanks.

Answer 1

I have achieved this by creating curving out memory from the lower part of the high memory for my device. To do this I modified my dtsi file to reflect the mew memory map as below:
/* 256MB at 0x0 - this is the low memory region*/
memory#0 {
device_type = "memory";
reg = <0x0 0x00000000 0x0 0x10000000>;
};
/* 1GB at 0x8010000000 - high memory region, this used to be 2GB earlier. I curved out to 1GB and allocated 1GB to my device*/
memory#8000000000 {
device_type = "memory";
reg = <0x80 0x10000000 0x0 0x40000000>;
};
/* 1GB carved out for my device.*/
my_device: mydevice#8050000000 {
compatible = "xxx,xxx-yyy";
reg = <0x00 0x20810000 0x0 0x010000>,
**<0x80 0x50000000 0x0 0x40000000>;**
interrupts = <GIC_SHARED xx IRQ_TYPE_LEVEL_HIGH>;
status = "disabled";
};
Allocation of 1GB was a bit too much and I have modified to it to 256MB but that is not important here.
Then in the driver I retried the memory details as below:
struct resource *res;
res = platform_get_resource(pdev, IORESOURCE_MEM, 0); /*this is to get hold of the the registers of my device*/
res = platform_get_resource(pdev, IORESOURCE_MEM, 1); /* this is the device memory for my device which had been set aside in the dtsi file above.*/
For using the memories retrieve as above use the below:
res->start /* start address of the memory region */
res->end - res->start + 1 /* this is to calculate the size of the memory*/
devm_ioremap_resource(&pdev->dev, res); /* this will give the mapped kernel virtual address for the memory bank*/