sifive fixes

[sorear]

FYI, the sifive_board is intended to use raw-format kernels not ELF; I think I fixed that earlier but it got lost?

[frantony]

FYI, the sifive_board is intended to use raw-format kernels not ELF; I think I fixed that earlier but it got lost?

You are right. As opposed to many popular qemu boards sifive_board is not intended to use ELF kernels.

I have used qemu sifive_board for porting barebox bootloader to RISC-V (https://www.spinics.net/lists/u-boot-v2/msg28603.html).

At the moment I use my own RISC-V qemu board for software emulation and the hw/sifive_board: get entry point address from kernel image patch is useless.

I'll update pull request after a short while.

[frantony]

@sorear , @sagark

Please review updated pull request.

[michaeljclark]

This makes a lot of sense i.e. re-use tested code.

I hadn't seen this PR before (partially) adding interrupts to sifive_uart.c and i've moved the constants into sifive_uart.h. It still will be quite easy to re-apply these changes.

And we also now have this PR https://github.com/riscv/riscv-qemu/pull/84

The current implementation interrupts on RX if SIFIVE_UART_IE_RXWM is set (assumes default 0 watermark)

We also need to do these things at some point:

• implement SIFIVE_UART_IE_TXWM interrupts
• implement Transmit FIFO full in txdata
• implement the rxctrl rxcnt field which specifies Rx FIFO watermark interrupt trigger threshold.
• implement the txctrl txcnt field which specifies Tx FIFO watermark interrupt trigger threshold.

And we need linux/drivers/tty/serial/sifive_uart.c so we can test it as it is the console UART on the sifive_u500 board (however SBI in bbl will currently drive the SiFive UART in polled mode).