-----Original Message----- From: Wolfgang Denk wd@denx.de Sent: Friday, October 26, 2018 4:57 PM To: Vabhav Sharma vabhav.sharma@nxp.com Cc: Marek Vasut marex@denx.de; u-boot@lists.denx.de; u-boot- dm@lists.denx.de; sjg@chromium.org; yamada.masahiro@socionext.com; bmeng.cn@gmail.com Subject: Re: [U-Boot-DM] [PATCH] drivers: serial: probe all serial devices
Dear Vabhav,
In message <VI1PR04MB48005B3CB205F14C4670CC2BF3F70@VI1PR04MB4800.eurprd04. prod.outlook.com> you wrote:
U-Boot does lazy initialization intentionally. It is wrong to initialize devices which are not actually used.
There is configuration option to enable the device using platform data or device tree using DM model.
"enable" means we have all required information needed to initialize them, if we need them. The need arises only when someone wants to transfer data over that UART. If nobody uses the UArt, there is no need to ever initialize it.
On u-boot, only one console is used There is need to use multiple console for network firmware logging, linux boot
Lazy initialization is a good thing - it saves resources, especially memory and time. Think for example of boot time optimizations...
I understand
For e.g: 2 UART controllers are enabled in device tree but DM model initialized only one, This is limitation
In which way is this a limitation? We use only one UART (for the serial console), so it works as supposed: only the used devices are fully initialized.
Limitation for aforesaid example
My suggestion is to initialize all devices which are enabled, E.g. use case is using UART1 for uboot consoled and UART2 for linux boot
What do you mean "for Linux boot"? If Linux needs the UART, it will initialize it itself in the Linux dvice driver.
Example is PL011 UART linux driver which expect initialization(integer and fractional baud date) done by bootloader
On NXP SoC, We also use UART3 for ethernet firmware logging but using DM model all enabled devices are not probed posing limitation.
Again, this is intentional, and not a limitation.
And what exactly do you mean by "UART3 for ethernet firmware logging"?
Different console than linux boot console.
Maybe you should rethink your software concept. We don't want to have a zillion of ports in used if not really necessary. Either you use standard channels (STDOUT, STDERR) for logging. Also, there used to be a syslog compatible logging driver.
Agree
I have a feeling that you attempt to do the Wong Thing.
I quoted the reason above and also discussed on in email(23 may) " [U-Boot-DM] QUERY:U-boot DM:SERIAL:Multiple On-chip UART Controller Support" with suggested solution from Simon which is sent as patch for review.
But Simon also explained "U-Boot only probes things in a 'lazy' manner so far", and there should be really good reasons for deviating from this principle. In no way should a "probe all devices" be made the default.
I see. Not default and config will be selected as required Sent patch has config option
And Andreas also wrote how to solve this issue in a board-specific way if it is really, really needed on some board.
However, you still fail to explain why you ned multiple serial ports in U-Boot running in parallel.
I am trying to convince you for the discussed problem faced recently in DM model
Best regards,
Wolfgang Denk
-- DENX Software Engineering GmbH, Managing Director: Wolfgang Denk HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd@denx.de Well, the way I see it, logic is only a way of being ignorant by num- bers. - Terry Pratchett, _Small Gods_