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

From: "Mukesh, Savaliya" <msavaliy@codeaurora.org>
To: Greg KH <gregkh@linuxfoundation.org>
Cc: akashast@codeaurora.org, linux-serial@vger.kernel.org,
	saravanak@google.com, sspatil@google.com, tkjos@google.com
Subject: Re: [PATCH V5] serial: msm_geni_serial_console : Add Earlycon support
Date: Mon, 22 Jun 2020 15:27:41 +0530	[thread overview]
Message-ID: <8aa2b407-f128-a679-defe-f66885e0ccee@codeaurora.org> (raw)
In-Reply-To: <20200522131308.GB1629195@kroah.com>

On 5/22/2020 6:43 PM, Greg KH wrote:
> 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?

Sure, patch is uploaded. We are removing this CONFIG and considering  no 
such config needed for now for

latest chipsets.

> 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...
I agree with the generic image change, we will work out on this later.
> thanks,
>
> greg k-h