Re: [PATCH v3] ARM: i.MX8M: esdctl: split memory banks for devices with >4G

[Sascha Hauer <sha@pengutronix.de>]

On Tue, Sep 05, 2023 at 11:32:10AM +0200, Marco Felsch wrote:
> At the moment the whole available memory is added to one single memory
> bank "ram0". This can cause barebox chainload issues on devices with a
> huge amount of memory like the i.MX8MP-EVK which has 6G of RAM if the
> barebox pbl binary is to large.
> 
> The reason for this issues is that memory_bank_first_find_space()
> returns the memory area with the largest amount of free space on the
> first memory bank. So in case of Debix SOM-A 8G and i.MX8MP-EVK 6G this
> is the area crossing the 4G boundary. This cause the barebox pbl code to
> trigger a MMU exception once the early MMU gets enabled which is
> configured for sizes <=4G.
> 
> Split the memory space into two memory banks: "ram0" and "ram1" to fix
> this issue.
> 
> Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>
> ---
> Changelog:
> v3:
> - add comment
> - add ifdef to fix 32bit compilation warning
> v2:
> - drop add_mem() usage and use arm_add_mem_device() directly
> ---
>  arch/arm/mach-imx/esdctl.c | 41 ++++++++++++++++++++++++++++++++++----
>  1 file changed, 37 insertions(+), 4 deletions(-)

Applied, thanks

Sascha

> 
> diff --git a/arch/arm/mach-imx/esdctl.c b/arch/arm/mach-imx/esdctl.c
> index 1798ad48e50a..2fca0a44a176 100644
> --- a/arch/arm/mach-imx/esdctl.c
> +++ b/arch/arm/mach-imx/esdctl.c
> @@ -510,16 +510,49 @@ static resource_size_t imx8m_ddrc_sdram_size(void __iomem *ddrc, unsigned buswid
>  				   reduced_adress_space, mstr);
>  }
>  
> +static int _imx8m_ddrc_add_mem(void *mmdcbase, struct imx_esdctl_data *data,
> +			       unsigned int buswidth)
> +{
> +	resource_size_t size = imx8m_ddrc_sdram_size(mmdcbase, buswidth);
> +	resource_size_t size0, size1;
> +	int ret;
> +
> +	/*
> +	 * Split the available memory into multiple banks if the device does
> +	 * have more RAM than 3G. At the moment this is necessary to prevent
> +	 * memory_bank_first_find_space() from finding free space near the end
> +	 * of the 4G barrier which is the case in a 6G/8G setup. This is
> +	 * important for larger barebox-pbl binaries (e.g. debug enabled) and
> +	 * the barebox chainloading mechanism since the pbl init the MMU to 4G.
> +	 * In this case a MMU exception will be thrown if the barebox-pbl is
> +	 * placed near the 4G barrier.
> +	 */
> +	size0 = min_t(resource_size_t, SZ_4G - MX8M_DDR_CSD1_BASE_ADDR, size);
> +	size1 = size - size0;
> +
> +	ret = arm_add_mem_device("ram0", data->base0, size0);
> +	if (ret || size1 == 0)
> +		return ret;
> +
> +#ifdef CONFIG_64BIT
> +	/*
> +	 * Albeit this hook is called on 64bit machines only, the driver serves
> +	 * 32bit machines as well. Guard the code to avoid compiler warnings.
> +	 */
> +	ret = arm_add_mem_device("ram1", SZ_4G, size1);
> +#endif
> +
> +	return ret;
> +}
> +
>  static int imx8m_ddrc_add_mem(void *mmdcbase, struct imx_esdctl_data *data)
>  {
> -	return arm_add_mem_device("ram0", data->base0,
> -			   imx8m_ddrc_sdram_size(mmdcbase, 32));
> +	return _imx8m_ddrc_add_mem(mmdcbase, data, 32);
>  }
>  
>  static int imx8mn_ddrc_add_mem(void *mmdcbase, struct imx_esdctl_data *data)
>  {
> -	return arm_add_mem_device("ram0", data->base0,
> -			   imx8m_ddrc_sdram_size(mmdcbase, 16));
> +	return _imx8m_ddrc_add_mem(mmdcbase, data, 16);
>  }
>  
>  static resource_size_t imx7d_ddrc_sdram_size(void __iomem *ddrc)
> -- 
> 2.39.2
> 
> 
> 

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