Re: [For 6.1 PATCH] hw/arm: xilinx_zynq: Disconnect the UART clocks temporarily

[Bin Meng]

On Sun, Aug 22, 2021 at 2:14 AM Peter Maydell <peter.maydell@linaro.org> wrote:
>
> On Sat, 21 Aug 2021 at 16:45, Bin Meng <bmeng.cn@gmail.com> wrote:
> >
> > As of today, when booting upstream U-Boot for Xilinx Zynq, the UART
> > does not receive anything. Initial debugging shows that the UART clock
> > frequency is 0 somehow which prevents the UART from receiving anything.
> > Note the U-Boot can still output data to the UART tx fifo, which should
> > not happen, as the design seems to prevent the data transmission when
> > clock is not enabled but somehow it only applies to the Rx side.
> >
> > For anyone who is interested to give a try, here is the U-Boot defconfig:
> > $ make xilinx_zynq_virt_defconfig
> >
> > and QEMU commands to test U-Boot:
> > $ qemu-system-arm -M xilinx-zynq-a9 -m 1G -display none -serial null 
> > -serial stdio \
> >     -device loader,file=u-boot-dtb.bin,addr=0x4000000,cpu-num=0
> >
> > Note U-Boot used to boot properly in QEMU 4.2.0 which is the QEMU
> > version used in current U-Boot's CI testing. The UART clock changes
> > were introduced by the following 3 commits:
> >
> > 38867cb7ec90 ("hw/misc/zynq_slcr: add clock generation for uarts")
> > b636db306e06 ("hw/char/cadence_uart: add clock support")
> > 5b49a34c6800 ("hw/arm/xilinx_zynq: connect uart clocks to slcr")
> >
> > Looks like we don't have enough time to figure out a proper fix before
> > 6.1.0 release date, let's disconnect the UART clocks temporarily.
>
> This is too late for 6.1 regardless, I'm afraid.

That's too bad :(

I figured out a proper fix, and will send it out soon.

Regards,
Bin