Hello Wolfgang,
On 14.07.2018 12:47, Wolfgang Denk wrote:
Dear Felix,
In message 1531492980-16543-1-git-send-email-fb@ltec.ch you wrote:
The motivation for writing this patch originates in the effort of synchronizing U-Boot DT to Linux DT for am33xx SOCs. The current am33xx.dtsi file from U-Boot defines the <reg-shift> property for all UART nodes. The actual (4.18+) am33xx.dtsi file from Linux does not define <reg-shift> anymore. To prevent (probably difficult) changes in many .dts and .dtsi files once the synchronization is done, one can use this new variable. For the pdu001 board, for example, SYS_NS16550_REG_SHIFT is set to 2; no need to clutter U-Boot and board specific dts files with <reg-shift> properties.
Does this mean that U-Boot will not be able to use the same DTB as Linux?
This has already been answered very accurately by Tom. I have also written an RFC dealing with this: "[RFC] arm: dts: am33xx: Sync DTS with Linux 4.16.11", posted May 24.
+config SYS_NS16550_REG_SHIFT
- int "Number of bytes to shift register offsets"
- default 0
- depends on SYS_NS16550
- help
Use this to specify the amount of bytes between discretedevice registers. If, for example, the device registers arelocated at 0x00, 0x04, 0x08, 0x0C and so forth than setthis to 2. The default value is 0.This description is inconsistent or misleading. How do you define "space between registers"? The unused gaps? In the example, the registers are spaced at 4 bytes intervals, so a value of 2 would only make sense of we have 16 bit registters and you count the gap bytes.
But this is a very strange and uncommon way to describe such a situation, especially when you write that you "shift register offsets". Here I think about something like a LSL operation, so shifing by 2 bits would result in a 2^2 = 4 byte spacing.
This needs to be rewritten.
You are right, sorry. It seems I used my brain to mix up two different explanations and that's the result - will be fixed.
Best regards,
Wolfgang Denk
regards, Felix