Hello Krzysztof, On Thu, Feb 23, 2023 at 10:12 AM Krzysztof Kozlowski <krzysztof.kozlowski@xxxxxxxxxx> wrote: > > On 22/02/2023 22:04, Martin Blumenstingl wrote: > > Amlogic G12A SoCs gained a new "divide XTAL by 2" bit. Everything else > > (we know about) is identical to the UART IP on GX (GXBB/GXL/GXM) SoCs. > > Add a new compatible string for this SoC so this new bit can be managed > > accordingly. > > > > Signed-off-by: Martin Blumenstingl <martin.blumenstingl@xxxxxxxxxxxxxx> > > --- > > Why am I sending this as RFC? The last change in this series means > > that the resulting .dtbs are not compatible with old kernels anymore. > > My understanding is that this is fine and only the opposite case (using > > old .dtbs on new kernels) has to be supported (which is still the case > > with this series). I'd like to get some confirmation for this. > > The other way around is also nice to have, because DTS is used in other > projects. You fixed here Linux kernel, but what about all other > out-of-tree kernels, BSDs, firmwares and bootloaders? Did you fix them > as well? Indeed, u-boot is of concern here (as mainline u-boot does have Meson G12A SoC support). > The question is whether the devices can be made compatible thus keeping > DTS working on older kernel. This commit suggests they are. Your DTS > commit is written in different tone - something was broken and is being > fixed. If we keep "amlogic,meson-gx-uart" as fallback compatible string then old kernels (or other .dtb consumers - like u-boot) would still work. Without the new "amlogic,meson-g12a-uart" compatible string we're unable to make use of a newly added clock divider within the UART IP block which allows baud rates such as 1500000 to work without (a lot of) jitter. Old kernels - with the new .dtb - would still be able to use serial (thanks to the "amlogic,meson-gx-uart" fallback compatible string) albeit with limited divider support (so not all baud rates can be used). Is this a valid plan? Best regards, Martin
