Hi Stuart,
On 06/02/2015 08:16 PM, Anderson, Stuart R wrote:
> Bin, et al,
>
> What we are losing here is the ability to specify a UART by its bus address
> instead of just supplying the memory or io address. There are some cases
> where this is useful, though I admit it is probably not going to be widely
> used. I have seen a platform where the location of the UART moves depending
> on the firmware version, but the bus address (B:D.F) did not change. There
> are also some platforms where you do not know the address until you boot the
> OS and can use the UART to login and find the address of the UART (oops.
> Chicken and egg problem).
The patch title and commit log are somewhat misleading.
What this patch actually does is re-implement pciserial earlyprintk
in terms of earlycon instead, so the functionality is retained.
Patch 1/2 adds pciserial support to earlycon with command line parameters
of the forms
earlycon=uart8250,pci[32],<B:D.F>,<options>
This patch 2/2
1. removes the x86-only pciserial bootconsole implementation, and
2. wires that behavior up to command line parameters of the forms
earlyprintk=uart8250,pci,<B:D.F>,<options>
which is not exactly what was suggested; rather that the existing
earlyprintk= command line format for pciserial should be transparently
handled by earlycon.
Regards,
Peter Hurley
> Also, I was going to soon send a patch to allow "pciserial32" for the case
> where the UART registers are 32-bit aligned instead of 8-bit aligned.
>
> Stuart
>
> -----Original Message-----
> From: Bin Gao [mailto:bin....@linux.intel.com]
> Sent: Tuesday, June 02, 2015 3:43 PM
> To: Thomas Gleixner
> Cc: Ingo Molnar; Ingo Molnar; H. Peter Anvin; Greg Kroah-Hartman; One
> Thousand Gnomes; Peter Hurley; Jiri Slaby; Borislav Petkov; Anderson, Stuart
> R; linux-kernel@vger.kernel.org
> Subject: Re: [PATCH v5 2/2] arch/x86: remove pci uart early console from
> early_prink.c
>
> On Tue, Jun 02, 2015 at 11:07:39PM +0200, Thomas Gleixner wrote:
>> What about the memory mapped uarts which have been source of trouble
>> in the past?
>>
>> Thanks,
>>
>> tglx
>
> Not sure which specific early console you are referring to.
> Currently we have serial, ttyS, vga, dbgp, xen, efi and pciserial in
> arch/x86/kernel/early_printk.c, and only pciserial is memory mapped (but it's
> being removed).
>
> And this patch only touches pciserial/serial parts so ideally shouldn't have
> impact on other early consoles.
>
> -Bin
>
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