Re: [PATCH] ARM: bootm: recalculate decompression space

[Sascha Hauer <s.hauer@pengutronix.de>]

On Fri, Jul 01, 2016 at 04:48:39PM +0200, Stefan Müller-Klieser wrote:
> According to the kernel documentation it is recommended to place the
> compressed image between 32 MiB and 128 MiB. The DTB and initrd should
> be placed above 128 MiB. We will follow the recommendation as long as we
> have enough RAM. If this is not the case, we fall back to the scheme.
> This change is required because of the ARM default kernel config changes
> regarding RODATA layout, which lead to an increased compression factor
> of the kernel image.
> This should be regarded as an intermediate solution until there is a
> mechanism for the kernel image to report the decompressed layout
> requirements to the bootloader.
> 
> Signed-off-by: Stefan Müller-Klieser <s.mueller-klieser@phytec.de>
> ---
>  arch/arm/lib/bootm.c | 18 +++++++++++++++---
>  1 file changed, 15 insertions(+), 3 deletions(-)

Applied, thanks.

Let's hope we don't have to revisit this too soon.

Sascha

> 
> diff --git a/arch/arm/lib/bootm.c b/arch/arm/lib/bootm.c
> index 803aa94..be1259b 100644
> --- a/arch/arm/lib/bootm.c
> +++ b/arch/arm/lib/bootm.c
> @@ -81,10 +81,15 @@ static int get_kernel_addresses(size_t image_size,
>  		return ret;
>  
>  	/*
> -	 * We don't know the exact decompressed size so just use a conservative
> -	 * default of 4 times the size of the compressed image.
> +	 * The kernel documentation "Documentation/arm/Booting" advises
> +	 * to place the compressed image outside of the lowest 32 MiB to
> +	 * avoid relocation. We should do this if we have at least 64 MiB
> +	 * of ram. If we have less space, we assume a maximum
> +	 * compression factor of 5.
>  	 */
> -	image_decomp_size = PAGE_ALIGN(image_size * 4);
> +	image_decomp_size = PAGE_ALIGN(image_size * 5);
> +	if (mem_size >= SZ_64M)
> +		image_decomp_size = max(image_decomp_size, SZ_32M);
>  
>  	/*
>  	 * By default put oftree/initrd close behind compressed kernel image to
> @@ -113,6 +118,13 @@ static int get_kernel_addresses(size_t image_size,
>  
>  	*mem_free = PAGE_ALIGN(*load_address + image_size + spacing);
>  
> +	/*
> +	 * Place oftree/initrd outside of the first 128 MiB, if we have space
> +	 * for it. This avoids potential conflicts with the kernel decompressor.
> +	 */
> +	if (mem_size > SZ_256M)
> +		*mem_free = max(*mem_free, mem_start + SZ_128M);
> +
>  	return 0;
>  }
>  
> -- 
> 1.9.1
> 
> 
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