On 4/3/2023 7:00 AM, Caleb James DeLisle wrote:
Hello folks,
I've been working on trying to port an en7526 and in doing so I'm trying
to learn how to at least partially write a DTS file from an old style
header full of #defines.
I ran into a bit of a quandry, I'm comparing the mt7621.dtsi file to an
older MT7621 memory map header:
https://github.com/openwrt/openwrt/blob/master/target/linux/ramips/dts/mt7621.dtsi#L100
https://github.com/keenetic/kernel-49/blob/master/arch/mips/include/asm/rt2880/rt_mmap.h#L48
```
palmbus: palmbus@1e000000 {
compatible = "palmbus";
reg = <0x1e000000 0x100000>;
ranges = <0x0 0x1e000000 0x0fffff>;
[...]
i2c: i2c@900 {
compatible = "mediatek,mt7621-i2c";
reg = <0x900 0x100>;
```
For me, means there should be an I2C controller mapped at address
0x1e000900.
Correct.
But looking at rt_mmap.h I see:
```
#define RALINK_I2C_BASE 0xBE000900
```
And in fact almost everything is based on 0xBE000000, except UART and
USB addresses which are "correct". And I see these 0xBE000000 addresses
being passed through KSEG1ADDR() so it seems they are physical memory
addresses, not virtual.
KSEG1ADDR does a logical or so it would not be altering RALINK_I2C_BASE
when OR'd with 0xa0000000 (KSEG1) you would still get 0xBE000900.
It seems to me like in places where it may be necessary to pass a
physical address they used physical addresses such that ioremap()
ends-up returning a proper kernel virtual address in KSEG1, however
everywhere else the driver might have just directly de-referenced the
constant which ends-up working just fine as well.
HTH
--
Florian
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