Re: [PATCH V5] serial: msm_geni_serial_console : Add Earlycon support

[Greg KH <gregkh@linuxfoundation.org>]

On Fri, May 22, 2020 at 06:13:06PM +0530, Mukesh, Savaliya wrote:
> From: Mukesh Kumar Savaliya <msavaliy@codeaurora.org>
> 
> This change enables earlyconsole support as static driver for geni
> based UART. Kernel space UART console driver will be generic for
> console and other usecases of UART.
> 
> Signed-off-by: Mukesh Kumar Savaliya <msavaliy@codeaurora.org>
> ---
> Changes In V2:
>  - Fixed Makefile Typo issue.
> 
> Changes In V3:
>  - Removed mb() calls as *_relaxed() should take care.
> 
> Changes In V4:
>  - Minor change: space between offset and base addition.
> 
> Changes In V5:
>  - Removed unlikely() macro.
>  - root_freq() array taken as static.
>  - Removed extra readback of the register having no meaning.
> 
>  drivers/tty/serial/Kconfig                   |  15 +
>  drivers/tty/serial/Makefile                  |   1 +
>  drivers/tty/serial/msm_geni_serial_console.c | 476 +++++++++++++++++++
>  3 files changed, 492 insertions(+)
>  create mode 100644 drivers/tty/serial/msm_geni_serial_console.c
> 
> diff --git a/drivers/tty/serial/Kconfig b/drivers/tty/serial/Kconfig
> index 0aea76cd67ff..ded19d80e696 100644
> --- a/drivers/tty/serial/Kconfig
> +++ b/drivers/tty/serial/Kconfig
> @@ -956,6 +956,21 @@ config SERIAL_MSM_CONSOLE
>  	select SERIAL_CORE_CONSOLE
>  	select SERIAL_EARLYCON
>  
> +config SERIAL_MSM_GENI_HALF_SAMPLING
> +	bool "Changes clock divider which impacts sampling rate for QUP HW ver greater than 2.5.0"
> +	help
> +	  Clock divider value should be doubled for QUP hardware version
> +	  greater than 2.5.0.
> +	  As earlycon can't have HW version awareness, decision is taken
> +	  based on the configuration.

Can you split this option out into a separate file so we don't have to
keep arguing about it, preventing the "real" early console code from
being merged?

I really think someone needs to go yell at some hardware engineers for
this issue.  How is this going to work for a "generic" arm64 kernel
image?  Your hardware always has to be self-describing for crazy stuff
like this.  Or you pass it in from the bootloader.  You can't hard-code
this thing, it defeats the whole idea of dynamic systems...

thanks,

greg k-h