[U-Boot] [U-Boot-DM] [PATCH] drivers: serial: probe all serial devices

From: Vabhav Sharma <vabhav.sharma@nxp.com>
To: u-boot@lists.denx.de
Subject: [U-Boot] [U-Boot-DM] [PATCH] drivers: serial: probe all serial devices
Date: Thu, 25 Oct 2018 14:19:25 +0000	[thread overview]
Message-ID: <VI1PR04MB48005B3CB205F14C4670CC2BF3F70@VI1PR04MB4800.eurprd04.prod.outlook.com> (raw)
In-Reply-To: <20181025140452.0D54A240044@gemini.denx.de>


> -----Original Message-----
> From: Wolfgang Denk <wd@denx.de>
> Sent: Thursday, October 25, 2018 7:35 PM
> To: Vabhav Sharma <vabhav.sharma@nxp.com>
> Cc: Marek Vasut <marex@denx.de>; u-boot at lists.denx.de; u-boot-
> dm at lists.denx.de; sjg at chromium.org; yamada.masahiro at socionext.com;
> bmeng.cn at gmail.com
> Subject: Re: [U-Boot-DM] [PATCH] drivers: serial: probe all serial devices
> 
> Dear Vabhav,
> 
> In message
> <VI1PR04MB48001E65CD3F477EC8CE6EB9F3F70@VI1PR04MB4800.eurprd04.
> prod.outlook.com> you wrote:
> >
> > > You can also use setenv stdin/stdout/stderr to alternate between
> > > stdio devices. So what is the problem ?
> > Problem is seen with PL011 driver using DM model, Only boot console
> baud rate is set.
> 
> U-Boot can talk to only one serial device at a time anyway, so why should it
> intiaalize othe rports than the one used for the (then
> current) console?
> 
> U-Boot does lazy initializationintentionally.  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.
For e.g: 2 UART controllers are enabled in device tree but DM model initialized only one, This is limitation
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 
On NXP SoC, We also use UART3 for ethernet firmware logging but using DM model all enabled devices are not probed  posing limitation
> 
> > Tried modifying the environment variable but seems readonly  (## Error
> > inserting "stdout" variable, errno=22)
> 
> How exactly did you try to do that?
#editenv stdout
> 
> > Multiple UART enablement is required to use all console.
> 
> 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.
Similar issue was faced by Andreas
> 
> 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 at denx.de I
> am an atheist, thank God!