Subject: [PATCH v1 3/4] arm64: Add arm64 kexec support

From: [email-masked] (Robin Murphy)
Date: Fri, 22 Jul 2016 11:03:14 +0100

On 22/07/16 05:08, Pratyush Anand wrote:
> On 21/07/2016:02:49:36 PM, Geoff Levand wrote:
>> On Thu, 2016-07-21 at 11:50 +0100, Robin Murphy wrote:
>>> The Exynos UART (drivers/tty/serial/samsung.c) is one which comes to
>>> mind as definitely existing, and on arm64 systems to boot. The TX
>>> register is at offset 0x20 there.
>>
>> Here's what I came up with.
>>
>>
>> +	struct data {const char *name; int tx_offset;};
>> +	static const struct data ok_list[] = {
>> +	/*	{"armada-3700-uart", ?},	*/
>> +		{"exynos4210-uart", 0x20},
>> +	/*	{"ls1021a-lpuart", ?},		*/
>> +	/*	{"meson-uart", ?},		*/
>> +	/*	{"mt6577-uart", ?},		*/
>> +		{"ns16550", 0},
>> +		{"ns16550a", 0},
>> +		{"pl011", 0},
>> +		{NULL, 0}
>> +	};
> 
> sinc functionality is just to debug the scenario when something goes wrong in
> purgatory. IMHO, it should be disabled by default. So, why not to keep it as
> simple as possible. Its a low level debugging mainly for developer, so user
> should know the absolute address. Therefore, I think no need to parse earlycon
> or earlyprintk from command line.  Whatever user passes in --port can be treated
> as address of TX register. If TX offset is 0x20, then user can pass --port as
> base+0x20. Additionally, we can pass TX register width as well. So what about
> something like "--port=0x1c020000,1" where 0x1c020000 is TX register address and
> 1 says about it's width in bytes.

I don't think even that is worthwhile, since without any polling it
still relies on the UART having FIFOs, someone having already enabled
the FIFOs, the FIFOs being deep enough and/or the output being short
enough. In short, it's fragile enough that I'm not convinced it's even
useful as a debug option. I suggest we simply copy the purgatory console
implementation from, say, ARM or Alpha.

Robin.

> ~Pratyush