[U-Boot] [PATCH 05/19] riscv: Add a SYSCON driver for Core Local Interruptor

[Bin Meng]

Hi Lukas,

On Tue, Nov 13, 2018 at 10:45 PM Auer, Lukas
<lukas.auer at aisec.fraunhofer.de> wrote:
>
> Hi Bin,
>
> On Tue, 2018-11-13 at 00:21 -0800, Bin Meng wrote:
> > This adds U-Boot syscon driver for RISC-V Core Local Interruptor
> > (CLINT). The CLINT block holds memory-mapped control and status
> > registers associated with software and timer interrupts.
> >
> > 3 APIs are provided for U-Boot to implement Supervisor Binary
> > Interface (SBI) as defined by the RISC-V privileged architecture
> > spec v1.10.
> >
> > Signed-off-by: Bin Meng <bmeng.cn at gmail.com>
> > ---
>
> Would it make sense to also abstract the functions provided by the
> CLINT more? The reason why I am asking is because the CLINT is
> (unfortunately) not specified as part of RISC-V. It is developing into
> a de facto standard since other platforms are following SiFive's
> implementation, but there is nothing that would prevent them from
> implementing something else.
>

I think your observation is correct about CLINT. Rick, does Andes's
RISC-V processor also follow SiFive's CLINT model?

> Two immediate examples I can think of would be mtime and the IPI
> implementation. Many SoC vendors will likely already have a suitable
> timer IP block for mtime. I can imagine that they would choose to re-
> use their memory map instead of following that of the CLINT.
> For the IPI implementation there is already an alternative, the SBI. If
> U-Boot should be able to run in supervisor mode, it would be helpful to
> support both the SBI and the CLINT interface.
>

I am not sure I followed you here. This driver provides 3 APIs:
riscv_send_ipi() is for IPI, and the other 2 are for mtime/mtimecmp.

> So what we would need is some kind of API for the functionality
> provided by the CLINT. For the multi-core support (I will try to send
> out a series soon) I am re-using the IRQ uclass ID (it is only used in
> arch code) to define a irq-uclass for RISC-V, which handles everything
> with IPIs. The CLINT0 and SBI are then just different driver
> implementing the uclass.
>
> This is just an idea right now, what do you think?
>

Regards,
Bin