Hi Lokesh, many thanks for the feedback! On 10.07.2018 08:42, Lokesh Vutla wrote: > Hi Felix, > > On Thursday 24 May 2018 02:32 PM, Felix Brack wrote: >> Hello, >> >> I am working on a patch to synchronize the DTS files of the am33xx SoC >> with those from Linux 4.16.11 (current stable). >> >> After some tiny modifications to the boards am335x-pdu001, am335x-evm, >> am335x-rut, am437x-gp-evm and am43x-epos-evm buildman passes without any >> warnings on the 46 am33xx based boards. This is required but not >> sufficient at all. >> >> As I'm the maintainer of the am335x-pdu001 board I will use it to >> illustrate a sample problem. >> The am335x-pdu001 board uses the ns16550 driver which reads the property >> <reg-shift> from the DT. This property is required and must be set to a >> value of 2, otherwise it would default to 0. >> The am33xx.dtsi file currently used by U-Boot sets this property >> correctly for all 6 uarts. The am33xx.dtsi file from Linux 4.16.11 >> however does not define this property anymore. >> For the am335x-pdu001 board the fix is trivial: just add the property >> <reg-shift> to the board and U-Boot specific am335xx-pdu001-u-boot.dtsi >> file. >> But this has a major drawback: only the am335x-pdu001 board gets fixed. >> What about other boards requiring the <reg-shift> property? > > I agree this is a problem. Also not all kernel drivers need this > property as there are separate driver files for some of the compatibles. > And few drivers has this property hard-coded. > >> The first idea that would probably come into mind is to put the property >> <reg-shift> into the SoC specific am33xx-u-boot.dtsi file. But this file >> is ignored if a board specific file already exists. Hence this can not >> be done. > > One solution I can think of is add a Kconfig entry > CONFIG_SYS_NS16550_REG_SHIFT. A default value of 0 can be assigned for > this and can be updated in as necessary. > > So when doing dev_read_u32_default for reg-shift, > CONFIG_SYS_NS16550_REG_SHIFT can be passed as default instead of 0. This > way no DTS files needs to be updated. > This sounds like a very good solution for the <reg-shift> property. I'm thinking about sending in a patch ...
> Thanks and regards, > Lokesh > >> >> For the patch I'm working on there is the general question about how to >> proceed. Should I just fix the board I'm maintaining and then post the >> patch? This would most certainly break some of the remaining 45 boards >> which I think is a no-go. >> >> A more specific question dealing with the "missing SoC property" >> <reg-shift> above is about <>-u-boot.dtsi files: would it be possible, >> useful and hazard-free to change the build process to use, for example, >> SoC specific _and_ board specific files? Of course some sort of >> hierarchy would be necessary to make sure that properties defined in the >> board specific dtsi file would overwrite the same properties defined in >> the SoC specific file ect. >> >> I believe that keeping DT files (especially include files) in sync >> between U-Boot and Linux is of big importance. Maybe there is already a >> standard solution to problems similar to the one depicted above. Anyway, >> I would appreciate any feedback. >> >> regards, Felix >> regards, Felix _______________________________________________ U-Boot mailing list U-Boot@lists.denx.de https://lists.denx.de/listinfo/u-boot
