[PATCH v2 1/4] tty: serial: Add 8250 earlycon to support noinit option

[Eddie Huang]

Hi Peter,

On Sun, 2015-02-01 at 21:24 -0800, Greg Kroah-Hartman wrote:
> On Mon, Feb 02, 2015 at 12:15:31AM -0500, Peter Hurley wrote:
> > On 02/01/2015 11:28 PM, Greg Kroah-Hartman wrote:
> > > On Sun, Feb 01, 2015 at 10:45:12PM -0500, Peter Hurley wrote:
> > >> On 02/01/2015 10:16 PM, Eddie Huang wrote:
> > 
> > >> I'll respin proper patches on top of Greg's tty-testing branch with reverts
> > >> for the noinit options. I noticed that one of the noinit patches actually
> > >> has the linkage for the mtk earlycon, so I'll be sure to preserve that.
> > > 
> > > I can just drop the patches in the tty-testing branch, that's what it is
> > > there for :)
> > > 
> > > Just let me know the specific patches and I will do so, thanks.
> > 
> > Well that pretty much means dropping the 3 patches that add earlycon to
> > 8250_mtk and then applying my patch (needs fixed to apply cleanly, which
> > I can do) and then applying a fixed-up replacement patch to add earlycon
> > to 8250_mtk (which I can also supply).
> > 
> > Is that the way you want to go?
> 
> Sounds good to me, send your patch, and I'll fix it all up tomorrow.
> 
> thanks,
> 
> greg k-h

Actually, your patch is a little different from my original idea.
Although my use case only care about divisor now, but other hardware
setting is still hard-code, not from parameter. In init_port()
function:   
	serial8250_early_out(port, UART_LCR, 0x3); /* 8n1 */
	serial8250_early_out(port, UART_IER, 0);/* no interrupt */
	serial8250_early_out(port, UART_FCR, 0); /* no fifo */
	serial8250_early_out(port, UART_MCR, 0x3); /* DTR + RTS */

This is why I propose a new option "noinit".

After checking further, in my case, I found that your patch should be
unnecessary because if skip baudrate, probe_baud() read DLL/DLM register
and init_port() write the same DLL/DLM value back, no touch any high
speed register, which means keep uart divisor setting as loader

Since I don't take "console=uart,mmio32,<addr>,noinit" into
consideration, it is good to drop my patches in the tty-testing branch.
For my case, I can send another series without noinit, just 8250_mtk.c
and its linkage modification in 8250_early.c

Eddie