linux-kernel - Re: [PATCH] ARM: boot: Fix ATAGs with appended DTB

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Message-ID: <e249c123-8d00-4aa3-34b8-f82d52428966@samsung.com>
Date:   Wed, 26 Feb 2020 07:35:14 +0100
From:   Marek Szyprowski <m.szyprowski@...sung.com>
To:     Geert Uytterhoeven <geert+renesas@...der.be>,
        Russell King <linux@...linux.org.uk>,
        Nicolas Pitre <nico@...xnic.net>,
        Arnd Bergmann <arnd@...db.de>,
        Eric Miao <eric.miao@...dia.com>,
        Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
Cc:     Chris Brandt <chris.brandt@...esas.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ARM: boot: Fix ATAGs with appended DTB

Hi Geert,

On 25.02.2020 15:47, Geert Uytterhoeven wrote:
> At early boot, register r8 may contain an ATAGs or DTB pointer.
> When an appended DTB is found, its address is stored in r8, for
> extraction of the RAM base address later.
>
> However, if r8 contained an ATAGs pointer before, that pointer will be
> lost, and the provided ATAGs is no longer folded into the provided DTB.
>
> Fix this by leaving r8 untouched.
>
> Fixes: 137e522593918be2 ("ARM: 8960/1: boot: Obtain start of physical memory from DTB")
> Reported-by: Marek Szyprowski <m.szyprowski@...sung.com>
> Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>
> ---
> Not tested with ATAGs, only with [uz]Image + DTB, and zImage with
> appended DTB.

Works fine with zImage + appended DTB + cmdline/memory info passed via ATAGs

Tested-by: Marek Szyprowski <m.szyprowski@...sung.com>

> ---
>   arch/arm/boot/compressed/head.S | 6 ++++--
>   1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm/boot/compressed/head.S b/arch/arm/boot/compressed/head.S
> index 339d4b4cfbbeed15..a351ed2bc195ed8d 100644
> --- a/arch/arm/boot/compressed/head.S
> +++ b/arch/arm/boot/compressed/head.S
> @@ -267,16 +267,18 @@ not_angel:
>   		cmp	r0, r1		@ do we have a DTB there?
>   		bne	1f
>   
> -		mov	r8, r6		@ use it if so
>   		/* preserve 64-bit alignment */
>   		add	r5, r5, #7
>   		bic	r5, r5, #7
> -		add	sp, sp, r5	@ and move stack above it
> +		add	sp, sp, r5	@ if so, move stack above DTB
> +		mov	r0, r6		@ and extract memory start from DTB
> +		b	2f
>   
>   1:
>   #endif /* CONFIG_ARM_APPENDED_DTB */
>   
>   		mov	r0, r8
> +2:
>   		bl	fdt_get_mem_start
>   		mov	r4, r0
>   		cmp	r0, #-1

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland