Hi Tom,
On 14.07.2018 17:49, Tom Rini wrote:
On Sat, Jul 14, 2018 at 12:47:21PM +0200, 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?
To be clear, it's the other way around. We can't use the Linux dtb/dts files as they've dropped (and in other cases, aren't adding) these properties as it's handled differently.
This is exactly the point. These files have diverged quite a lot between U-Boot and Linux since the last synchronization. I am trying to find a method to re-synchronize U-Boot generating minimal collateral damage - this patch is supposed to be part of that effort.
In fact we could even set the default value of SYS_NS16550_REG_SHIFT to 2 for _all_ am33xx SOC boards. That would probably further reduce possible problems.
+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.
To try and help clarify, the property in question means "quantity to shift the register offsets by." It should be clear in our Kconfig help entry as well that this is what we're looking for.
Thanks for this! The help text will be fixed in v2.
regards Felix