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From: Ahmad Fatoum <a.fatoum@pengutronix.de>
To: Sascha Hauer <s.hauer@pengutronix.de>, Ahmad Fatoum <ahmad@a3f.at>
Cc: barebox@lists.infradead.org
Subject: Re: [PATCH 1/3] ARM: i.MX: boot: correctly handle SRC_SBMR1 override via SRC_GPR9
Date: Mon, 27 Apr 2020 10:28:42 +0200	[thread overview]
Message-ID: <ccef9a1d-0887-7573-966d-fee2eba57907@pengutronix.de> (raw)
In-Reply-To: <20200427080727.GO5877@pengutronix.de>

Hello,

On 4/27/20 10:07 AM, Sascha Hauer wrote:
> On Mon, Apr 27, 2020 at 09:13:49AM +0200, Ahmad Fatoum wrote:
>> `mw 0x20d8040 0x08000030; mw 0x20d8044 0x10000000; reset` issued on an
>> i.MX6Q forces boot from the ecspi1. This is because the BootROM reads
>> the boot mode out of SRC_GPR9 instead of SRC_SBMR1 whenever SRC_GPR10
>> has its 28th bit set.
> 
> Is this documented somewhere? The reference Manual marks SRC_GPR9 and
> SRC_GPR10 as
> 
> | This register is used by the ROM code and should not be used
> | by application software.

Not documented anywhere, except for U-Boot's bmode command and boot
source determination code:

https://github.com/trini/u-boot/blob/v2020.04/arch/arm/mach-imx/mx6/soc.c#L560
https://github.com/trini/u-boot/blob/v2020.04/arch/arm/mach-imx/init.c#L104

> And why do you depend on this behaviour?

It's a useful debugging aid, when strap pins aren't easily accessible,
because then your only other option is then to fuse to affect the boot
(or short your SPI I/O pins).

I am preparing code to provide a generic reboot mode functionality
in barebox. This would among others cover the functionality of
the U-Boot bmode command and these patches here are prerequisites,
so the boot source detection remains accurate.

Cheers


> 
> Sascha
> 

-- 
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  reply	other threads:[~2020-04-27  8:28 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-04-27  7:13 Ahmad Fatoum
2020-04-27  7:13 ` [PATCH 2/3] ARM: i.MX: boot: interpret reserved boot as forced serial Ahmad Fatoum
2020-04-27  7:13 ` [PATCH 3/3] ARM: i.MX6: boot: handle i.MX6UL differences Ahmad Fatoum
2020-04-27  8:07 ` [PATCH 1/3] ARM: i.MX: boot: correctly handle SRC_SBMR1 override via SRC_GPR9 Sascha Hauer
2020-04-27  8:28   ` Ahmad Fatoum [this message]
2020-05-08  6:41     ` Ahmad Fatoum
2020-05-08 12:07       ` Sascha Hauer

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