Hi Cédric, Peter, On Tue, 31 Aug 2021, at 20:09, Cédric Le Goater wrote: > On 8/28/21 5:58 PM, Peter Delevoryas wrote: > > I think I’m a little confused on this part. What I meant by “most machines > > just use UART5” was that most DTS’s use “stdout-path=&uart5”, but fuji uses > > “stdout-path=&uart1”. I /do/ see that SCU510 includes a bit related to > > UART, but it’s for disabling booting from UART1 and UART5. I just care > > about the console aspect, not booting. > > The UART can be switched with SCU70[29] on the AST2500, btw.
If it helps, neither the AST2600's "Boot from UART" feature nor the AST2[456]00's "Debug UART" feature are related to which UART is used as the BMC console by u-boot and/or the kernel - the latter is entirely a software thing. The "Debug UART" is a hardware backdoor, a UART-to-AHB bridge implemented by the SoC. It provides a shell environment that allows you to issue transactions directly on the AHB if you perform a magic knock. I have a driver for it implemented here: https://github.com/amboar/cve-2019-6260/blob/master/src/debug.c SCU70[29] on the AST2500 selects whether this backdoor is exposed on UART1 or UART5. The "Boot from UART" feature is implemented in the AST2600 ROM code as a fallback for loading the SPL if fetching it from SPI-NOR or the eMMC fails, or the SPL is incorrectly signed for secure-boot. I think Peter is on the right track with this patch? Andrew
