Re: [PATCH v1 0/6] x86/boot: Enable earlyprintk on MMIO (8-bit)

[Andy Shevchenko <andriy.shevchenko@linux.intel.com>]

On Tue, May 06, 2025 at 12:38:21PM -0700, David Woodhouse wrote:
> On Fri, 2025-05-02 at 15:29 +0300, Andy Shevchenko wrote:
> > Some of the platforms may have no legacy COM ports and only provide
> > an MMIO accessible UART. Add support for such to earlyprintk for the
> > boot phase of the kernel.
> 
> Aha, I understand now... you've added this *only* for the boot code,
> and haven't added the corresponding support to the in-kernel
> earlyprintk, in arch/x86/kernel/early_printk.c

Haven't added yet. This is part 1 only.

> The latter does already support MMIO but it only supports a 32-bit
> stride, not 8-bit.
> 
> Please could you make that consistent, and ensure the earlyprintk=
> arguments function the same for both phases? I'm happy to add the
> kexec-debug parts on top of *that*.

It's not as easy as it looks like. I had done in the past the comparison table
of what we have between all early*=... for serial consoles and it all so
inconsistent to begin with. A big work needs to be fulfilled in order to put
this mess in order. Hence this is just the first step.

> It would be really helpful if we could test this in QEMU; it shouldn't
> be that hard to make it provide a 16550 on MMIO, along the lines of the
> one-line hack I posted yesterday.

I understand. But if no go for this series, I don't won't to spend time on
the next part.

In any case, thanks for looking into this.

-- 
With Best Regards,
Andy Shevchenko