[PATCH v2] drivers: serial: probe all uart devices

[Stefan Roese]

Hi Vabhav,

On 14.10.20 13:15, Vabhav Sharma (OSS) wrote:
> Hi Stefan,
> Sorry for delayed reply, Occupied with high priority task
> 
>> -----Original Message-----
>> From: Stefan Roese <sr at denx.de>
>> Sent: Wednesday, September 30, 2020 10:46 AM
>> To: Vabhav Sharma (OSS) <vabhav.sharma at oss.nxp.com>;
>> andre.przywara at arm.com; u-boot at lists.denx.de; sjg at chromium.org
>> Cc: Vabhav Sharma <vabhav.sharma at nxp.com>
>> Subject: Re: [PATCH v2] drivers: serial: probe all uart devices
>>
>> On 29.09.20 19:26, Vabhav Sharma wrote:
>>> From: Vabhav Sharma <vabhav.sharma at nxp.com>
>>>
>>> U-Boot DM model probe only single device at a time which is enabled
>>> and configured using device tree or platform data method.
>>>
>>> PL011 UART IP is SBSA compliant and firmware does the serial port
>>> set-up, initialization and let the kernel use UART port for sending
>>> and receiving characters.
>>>
>>> Normally software talk to one serial port time but some LayerScape
>>> platform require all the UART devices enabled in Linux for various use
>>> case.
>>>
>>> Adding support to probe all enabled serial devices like SBSA compliant
>>> PL011 UART ports probe and initialization by firmware.
>>>
>>> Signed-off-by: Vabhav Sharma <vabhav.sharma at nxp.com>
>>> ---
>>> v2:
>>>      Incorporated Stefan review comment, Update #ifdef with macro
>>>      if (IS_ENABLED)..
>>
>> Better, thanks. But...
>>
>>> ---
>>> ---
>>>    drivers/serial/Kconfig         | 17 +++++++++++++++++
>>>    drivers/serial/serial-uclass.c | 30 ++++++++++++++++++++++++++++++
>>>    2 files changed, 47 insertions(+)
>>>
>>> diff --git a/drivers/serial/Kconfig b/drivers/serial/Kconfig index
>>> e344677..b2e30f1 100644
>>> --- a/drivers/serial/Kconfig
>>> +++ b/drivers/serial/Kconfig
>>> @@ -134,6 +134,23 @@ config SERIAL_SEARCH_ALL
>>>
>>>    	  If unsure, say N.
>>>
>>> +config SERIAL_PROBE_ALL
>>> +	bool "Probe all available serial devices"
>>> +	depends on DM_SERIAL
>>> +	default n
>>> +	help
>>> +	  The serial subsystem only probe for single serial device,
>>> +	  but does not probe for other remaining serial devices.
>>> +	  With this option set,we make probing and searching for
>>> +	  all available devices optional.
>>> +	  Normally, U-Boot talk to one serial port at a time but SBSA
>>> +	  compliant UART devices like PL011 require initialization
>>> +	  by firmware and let the kernel use serial port for sending
>>> +	  and receiving the characters.
>>> +
>>> +	  If probing is not required for all remaining available
>>> +	  devices other than default current console device, say N.
>>> +
>>>    config SPL_DM_SERIAL
>>>    	bool "Enable Driver Model for serial drivers in SPL"
>>>    	depends on DM_SERIAL && SPL_DM
>>> diff --git a/drivers/serial/serial-uclass.c
>>> b/drivers/serial/serial-uclass.c index 0027625..d303a66 100644
>>> --- a/drivers/serial/serial-uclass.c
>>> +++ b/drivers/serial/serial-uclass.c
>>> @@ -86,6 +86,11 @@ static void serial_find_console_or_panic(void)
>>>    		uclass_first_device(UCLASS_SERIAL, &dev);
>>>    		if (dev) {
>>>    			gd->cur_serial_dev = dev;
>>> +			if (IS_ENABLED(CONFIG_SERIAL_PROBE_ALL)) {
>>> +				/* Scanning uclass to probe all devices */
>>> +				for (; dev; uclass_next_device(&dev))
>>> +					;
>>> +			}
>>>    			return;
>>>    		}
>>>    	} else if (CONFIG_IS_ENABLED(OF_CONTROL) && blob) { @@ -96,11
>>> +101,21 @@ static void serial_find_console_or_panic(void)
>>>    			if (np
>> && !uclass_get_device_by_ofnode(UCLASS_SERIAL,
>>>    					np_to_ofnode(np), &dev)) {
>>>    				gd->cur_serial_dev = dev;
>>> +				if (IS_ENABLED(CONFIG_SERIAL_PROBE_ALL))
>> {
>>> +					/* Scanning uclass to probe devices
>> */
>>> +					for (; dev; uclass_next_device(&dev))
>>> +						;
>>> +				}
>>
>> This code sequence (incl. gd->cur_serial_dev = dev;) is repeated multiple
>> times (below as well). Could you instead move this into a function and call
>> this function to reduce code and binary size?
> I understand.
> Checked and found that 56 bytes of code is added (including enabling
> the macro on LS platform)
> 
> Intended to define it earlier but defining one line of code in a
> function cause more overhead (function call, Stack operations,
> Pointer arithmetic) in execution time.

So you did measure a penalty in bootup time with this code moved
into a function? I would have thought that this is neglectable.

> Tradeoff is to choose between Function overhead Vs Binary Size, What
> is your suggestion

My vote is for the function. Mainly not because of the smaller image
size, but because of the smaller source code base, being easier to
maintain (IMHO).

Thanks,
Stefan

>>
>> Thanks,
>> Stefan
>>
>>>    				return;
>>>    			}
>>>    		} else {
>>>    			if (!serial_check_stdout(blob, &dev)) {
>>>    				gd->cur_serial_dev = dev;
>>> +				if (IS_ENABLED(CONFIG_SERIAL_PROBE_ALL))
>> {
>>> +					/* Scanning uclass to probe devices
>> */
>>> +					for (; dev; uclass_next_device(&dev))
>>> +						;
>>> +				}
>>>    				return;
>>>    			}
>>>    		}
>>> @@ -125,6 +140,11 @@ static void serial_find_console_or_panic(void)
>>>    		    !uclass_get_device(UCLASS_SERIAL, INDEX, &dev)) {
>>>    			if (dev->flags & DM_FLAG_ACTIVATED) {
>>>    				gd->cur_serial_dev = dev;
>>> +				if (IS_ENABLED(CONFIG_SERIAL_PROBE_ALL))
>> {
>>> +					/* Scanning uclass to probe devices
>> */
>>> +					for (; dev; uclass_next_device(&dev))
>>> +						;
>>> +				}
>>>    				return;
>>>    			}
>>>    		}
>>> @@ -136,6 +156,11 @@ static void serial_find_console_or_panic(void)
>>>    			if (!ret) {
>>>    				/* Device did succeed probing */
>>>    				gd->cur_serial_dev = dev;
>>> +				if (IS_ENABLED(CONFIG_SERIAL_PROBE_ALL))
>> {
>>> +					/* Scanning uclass to probe devices
>> */
>>> +					for (; dev; uclass_next_device(&dev))
>>> +						;
>>> +				}
>>>    				return;
>>>    			}
>>>    		}
>>> @@ -144,6 +169,11 @@ static void serial_find_console_or_panic(void)
>>>    		    !uclass_get_device(UCLASS_SERIAL, INDEX, &dev) ||
>>>    		    (!uclass_first_device(UCLASS_SERIAL, &dev) && dev)) {
>>>    			gd->cur_serial_dev = dev;
>>> +			if (IS_ENABLED(CONFIG_SERIAL_PROBE_ALL)) {
>>> +				/* Scanning uclass to probe all devices */
>>> +				for (; dev; uclass_next_device(&dev))
>>> +					;
>>> +			}
>>>    			return;
>>>    		}
>>>    #endif
>>>
>>
>>
>> Viele Grüße,
>> Stefan
>>
>> --
>> DENX Software Engineering GmbH,      Managing Director: Wolfgang Denk
>> HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
>> Phone: (+49)-8142-66989-51 Fax: (+49)-8142-66989-80 Email: sr at denx.de


Viele Grüße,
Stefan

-- 
DENX Software Engineering GmbH,      Managing Director: Wolfgang Denk
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
Phone: (+49)-8142-66989-51 Fax: (+49)-8142-66989-80 Email: sr at denx.de