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 <[email protected]> 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 discrete >>> + device registers. If, for example, the device registers are >>> + located at 0x00, 0x04, 0x08, 0x0C and so forth than set >>> + this 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 _______________________________________________ U-Boot mailing list [email protected] https://lists.denx.de/listinfo/u-boot
