Re: [PATCH v6 13/15] MIPS: JZ4770: Workaround for corrupted DMA transfers

[James Hogan <james.hogan@mips.com>]

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On Fri, Jan 05, 2018 at 07:25:11PM +0100, Paul Cercueil wrote:
> From: Maarten ter Huurne <maarten@treewalker.org>
> 
> We have seen MMC DMA transfers read corrupted data from SDRAM when
> a burst interval ends at physical address 0x10000000. To avoid this
> problem, we remove the final page of low memory from the memory map.
> 
> Signed-off-by: Maarten ter Huurne <maarten@treewalker.org>
> ---
>  arch/mips/jz4740/setup.c | 24 ++++++++++++++++++++++++
>  arch/mips/kernel/setup.c |  8 ++++++++
>  2 files changed, 32 insertions(+)
> 
>  v2: No change
>  v3: No change
>  v4: No change
>  v5: No change
>  v6: No change
> 
> diff --git a/arch/mips/jz4740/setup.c b/arch/mips/jz4740/setup.c
> index cd89536fbba1..18c57c4bf47e 100644
> --- a/arch/mips/jz4740/setup.c
> +++ b/arch/mips/jz4740/setup.c
> @@ -22,6 +22,7 @@
>  #include <linux/of_fdt.h>
>  
>  #include <asm/bootinfo.h>
> +#include <asm/page.h>
>  #include <asm/prom.h>
>  
>  #include <asm/mach-jz4740/base.h>
> @@ -103,3 +104,26 @@ void __init arch_init_irq(void)
>  {
>  	irqchip_init();
>  }
> +
> +/*
> + * We have seen MMC DMA transfers read corrupted data from SDRAM when a burst
> + * interval ends at physical address 0x10000000. To avoid this problem, we
> + * remove the final page of low memory from the memory map.
> + */
> +void __init jz4770_reserve_unsafe_for_dma(void)
> +{
> +	int i;
> +
> +	for (i = 0; i < boot_mem_map.nr_map; i++) {
> +		struct boot_mem_map_entry *entry = boot_mem_map.map + i;
> +
> +		if (entry->type != BOOT_MEM_RAM)
> +			continue;
> +
> +		if (entry->addr + entry->size != 0x10000000)
> +			continue;
> +
> +		entry->size -= PAGE_SIZE;
> +		break;
> +	}
> +}
> diff --git a/arch/mips/kernel/setup.c b/arch/mips/kernel/setup.c
> index 85bc601e9a0d..5a2c20145aee 100644
> --- a/arch/mips/kernel/setup.c
> +++ b/arch/mips/kernel/setup.c
> @@ -879,6 +879,14 @@ static void __init arch_mem_init(char **cmdline_p)
>  
>  	parse_early_param();
>  
> +#ifdef CONFIG_MACH_JZ4770
> +	if (current_cpu_type() == CPU_JZRISC &&
> +				mips_machtype == MACH_INGENIC_JZ4770) {
> +		extern void __init jz4770_reserve_unsafe_for_dma(void);
> +		jz4770_reserve_unsafe_for_dma();
> +	}
> +#endif

Hmm, a little bit ugly. I'm guessing the plat_mem_setup() callback is
too early since mem= parameters won't have been taken into account yet
from parse_early_param().

Is /memreserve/ in FDT of any value here or is it all too late due to
old DTs?

Cheers
James

> +
>  	if (usermem) {
>  		pr_info("User-defined physical RAM map:\n");
>  		print_memory_map();
> -- 
> 2.11.0
> 
> 

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