Re: [PATCH 09/12] i386/x86_64: EHCI usb debug port early printk support.

[Andi Kleen]

Thanks for writing that code. It should be an interesting alternative
on boxes where firescope doesn't work.

I hope I can eventually merge early firewire support code too.

On Mon, Apr 30, 2007 at 10:32:02AM -0600, Eric W. Biederman wrote:
> 
> With legacy free systems serial ports have stopped being an option
> to get early boot traces and other debug information out of a machine.

This needs a CONFIG_* at least. And some documentation on how to set it
up on both sides.

> 
> This debug device can be used to replace serial ports for
> kgdb, kdb, and console support.  And gregkh has a simple usb
> serial driver for it so user space applications that control
> serial ports should work unmodified.

But not merged yet, right? I was hoping it could be done from
user space anyways.

> For users the hard part looks like it will be finding cables and
> finding which is usb debug port 1 and realizing that there is
> flow control so the kernel boot will not happen if someone is not
> reading the serial console data.

That's nasty. Any way to work around that?

> index 92213d2..dc097aa 100644
> --- a/arch/x86_64/kernel/early_printk.c
> +++ b/arch/x86_64/kernel/early_printk.c
> @@ -3,9 +3,19 @@
>  #include <linux/init.h>
>  #include <linux/string.h>
>  #include <linux/screen_info.h>
> +#include <linux/usb/ch9.h>
> +#include <linux/pci_regs.h>
> +#include <linux/pci_ids.h>
> +#include <linux/errno.h>

Can you put it in a separate file please?
Perhaps with a little abstraction in drivers/usb ? 

> +static void dbgp_breath(void)
> +{
> +	/* Sleep to give the debug port a chance to breathe */

But you don't?

> +static __u32 __init find_dbgp(int ehci_num, unsigned *rbus, unsigned *rslot, unsigned *rfunc)

This should be probably merged into the early quirks loop

>   		early_console = &simnow_console;
>   		keep_early = 1;
> +	} else if (!strncmp(buf, "dbgp", 4)) {

usb would seem to be more intuitive

-Andi
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