linux-kernel - Re: [PATCH 5/6] ARM: add low level debug uart for rk1108

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Date:   Fri, 04 Nov 2016 09:03:19 +0100
From:   Heiko Stuebner <heiko@...ech.de>
To:     Andy Yan <andy.yan@...k-chips.com>
Cc:     mturquette@...libre.com, linux-rockchip@...ts.infradead.org,
        linux@...linux.org.uk, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/6] ARM: add low level debug uart for rk1108

Am Freitag, 4. November 2016, 15:58:35 CET schrieb Andy Yan:
> Hi Heiko:
> 
> On 2016年11月04日 15:36, Heiko Stuebner wrote:
> > Am Donnerstag, 3. November 2016, 20:42:21 CET schrieb Andy Yan:
> >> RK1108 UARTs are Synopsis DesignWare 8250 compatible.
> >> Only with different register addresses.
> >> 
> >> Signed-off-by: Andy Yan <andy.yan@...k-chips.com>
> >> ---
> >> 
> >>   arch/arm/Kconfig.debug | 30 ++++++++++++++++++++++++++++++
> >>   1 file changed, 30 insertions(+)
> >> 
> >> diff --git a/arch/arm/Kconfig.debug b/arch/arm/Kconfig.debug
> >> index d83f7c3..408540f 100644
> >> --- a/arch/arm/Kconfig.debug
> >> +++ b/arch/arm/Kconfig.debug
> >> @@ -776,6 +776,30 @@ choice
> >> 
> >>   		  their output to the standard serial port on the RealView
> >>   		  PB1176 platform.
> >> 
> >> +	config DEBUG_RK1108_UART0
> >> +		bool "Kernel low-level debugging messages via Rockchip RK1108 
UART0"
> >> +		depends on ARCH_ROCKCHIP
> >> +		select DEBUG_UART_8250
> >> +		help
> >> +		  Say Y here if you want kernel low-level debugging support
> >> +                  on Rockchip RK1108 based platforms.
> >> +
> >> +	config DEBUG_RK1108_UART1
> >> +		bool "Kernel low-level debugging messages via Rockchip RK1108 
UART1"
> >> +		depends on ARCH_ROCKCHIP
> >> +		select DEBUG_UART_8250
> >> +		help
> >> +		  Say Y here if you want kernel low-level debugging support
> >> +		  on Rockchip RK1108 based platforms.
> >> +
> >> +	config DEBUG_RK1108_UART2
> >> +		bool "Kernel low-level debugging messages via Rockchip RK1108 
UART2"
> >> +		depends on ARCH_ROCKCHIP
> >> +		select DEBUG_UART_8250
> >> +		help
> >> +		  Say Y here if you want kernel low-level debugging support
> >> +		  on Rockchip RK1108 based platforms.
> >> +
> > 
> > are you sure, you need all 3 of them?
> > 
> > I.e. most Rockchip SoCs so far had one uart somewhat designated as debug
> > uart. Most likely due to it not having rts/cts and being used in
> > reference schematics, but no one ever used another uart than uart2 on
> > previous socs. So ideally we could check and only add uarts we actually
> > need for now. More can be added later anyway once boards try to use them.
> > 
> > 
> > Heiko
> 
>      Actually, I have two boards on my hand, one uses uart0 as debug
> port and the another uses uart2, so I add all of them here.

ok, then this is fine.

>     I have a question here, I not very clear how to get the
> DEBUG_UART_VIRT value here,  I now set the value I got from uart driver
> and it works , is there some rule or  method to calculate this
> DEBUG_UART_VIRT value on different platform?

I don't really know. When I added the old uarts, I always just took the value 
from the vendor-kernel :-) .

In any case, arm32 now also supports earlycon (like arm64) not needing the 
bootloader setup of the uart. The one thing debug_ll can do that earlycon 
cannot is outputting stuff from the kernel decompressor.


Heiko