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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] serial: msm_geni_serial_console : Add Earlycon support
Date: Wed, 6 May 2020 17:01:52 +0530	[thread overview]
Message-ID: <9dd11375-7f6e-8e3d-6243-89089a938f01@codeaurora.org> (raw)
In-Reply-To: <20200429173826.GB2332435@kroah.com>


On 4/29/2020 11:08 PM, Greg KH wrote:
> On Wed, Apr 29, 2020 at 10:49:34PM +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>
>> ---
>>   drivers/tty/serial/Kconfig                   |  15 +
>>   drivers/tty/serial/Makefile                  |   1 +
>>   drivers/tty/serial/msm_geni_serial_console.c | 525 +++++++++++++++++++
>>   3 files changed, 541 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.
> How do we know this?  Can't this be dynamically determined at runtime?
> What about kernels that want to be built for both types of hardware at
> the same time?

This will vary for different hardware only if QUP version is lower than 
this.

We can not determine this dynamically because register address space to 
read QUP version is in QUP wrapper space and that also keep varying per 
target.

we only  get internal SE address base in cmdline arg.

>
>> +	  As earlycon can't have HW version awareness, decision is taken
>> +	  based on the configuration.
>> +
>> +config SERIAL_MSM_GENI_EARLY_CONSOLE
>> +	bool "MSM on-chip GENI HW based early console support"
>> +	select SERIAL_MSM_GENI_HALF_SAMPLING
>> +	help
>> +	  Serial early console driver for Qualcomm Technologies Inc's GENI
>> +	  based QUP hardware.
> Why can't we have early console without SERIAL_MSM_GENI_HALF_SAMPLING?
>
> Why are these tied directly to each other?  Do you really need 2
> options?
HALF_SAMPLING controlls the sampling rate of UART HW, if not then logs 
come garbled due to wrong sampling.
>
>> +
>>   config SERIAL_QCOM_GENI
>>   	tristate "QCOM on-chip GENI based serial port support"
>>   	depends on ARCH_QCOM || COMPILE_TEST
>> diff --git a/drivers/tty/serial/Makefile b/drivers/tty/serial/Makefile
>> index d056ee6cca33..9790ef2d802c 100644
>> --- a/drivers/tty/serial/Makefile
>> +++ b/drivers/tty/serial/Makefile
>> @@ -55,6 +55,7 @@ obj-$(CONFIG_SERIAL_VR41XX) += vr41xx_siu.o
>>   obj-$(CONFIG_SERIAL_ATMEL) += atmel_serial.o
>>   obj-$(CONFIG_SERIAL_UARTLITE) += uartlite.o
>>   obj-$(CONFIG_SERIAL_MSM) += msm_serial.o
>> +obj-$(SERIAL_MSM_GENI_EARLY_CONSOLE) += msm_geni_serial_console.o
> I don't think you tested this at all :(
>
> I've stopped here in the review for this obvious reason...

Done the changes. Sorry, i compiled with the static config but missed to 
add back when compiled with  config change.

Uploaded new change.

>
> thanks,
>
> greg k-h

  reply	other threads:[~2020-05-06 11:32 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-04-29 17:19 [PATCH] serial: msm_geni_serial_console : Add Earlycon support Mukesh, Savaliya
2020-04-29 17:38 ` Greg KH
2020-05-06 11:31   ` Mukesh, Savaliya [this message]
2020-05-06 11:46     ` Greg KH

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