Re: [PATCH v2] sunxi: dram: detect non-power-of-2 sized DRAM chips

["Jernej Škrabec" <jernej.skrabec@gmail.com>]

Dne ponedeljek, 19. januar 2026 ob 00:59:05 Srednjeevropski standardni čas je Andre Przywara napisal(a):
> Some boards feature an "odd" DRAM size, where the total RAM is 1.5GB or
> 3GB. Our existing DRAM size detection routines can only detect power-of-2
> sized configuration, and on those boards the DRAM size is overestimated,
> so this typically breaks the boot quite early.
> 
> There doesn't seem to be an easy explicit way to detect those odd-sized
> chips, but we can test whether the later part of the memory behaves like
> memory, by verifying that a written pattern can be read back.
> Experiments show that there is no aliasing effect here, as all locations
> in the unimplemented range always return some fixed pattern, and cannot
> be changed.
> 
> Also so far all those boards use a factor of 3 of some lower power-of-2
> number, or 3/4th of some higher number. The size detection routine
> discovers the higher number, so we can check for some memory cells beyond
> 75% of the detected size to be legit.
> 
> Add a routine the inverts all bits at a given location in memory, and
> reads that back to prove that the new value was stored.
> Then test the memory cell at exactly 3/4th of the detected size, and cap
> the size of the memory to 75% when this test fails. For good measure
> also make sure that memory just below the assumed memory end really
> works.
> 
> This enables boards which ship with such odd memory sizes.
> 
> Signed-off-by: Andre Przywara <andre.przywara@arm.com>
> ---
> Hi,
> 
> v2 just adds the "positive" check, so whether memory just below 3/4th is
> accessible, when the test for above 3/4th failed.
> Please test if you have a board with such "odd"-sized DRAM.
> 
> Cheers,
> Andre

This looks good to me now!

Reviewed-by: Jernej Skrabec <jernej.skrabec@gmail.com>

Best regards,
Jernej

> 
>  arch/arm/include/asm/arch-sunxi/dram.h |  1 +
>  arch/arm/mach-sunxi/dram_dw_helpers.c  | 22 +++++++++++++++++++++-
>  arch/arm/mach-sunxi/dram_helpers.c     | 12 ++++++++++++
>  3 files changed, 34 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm/include/asm/arch-sunxi/dram.h b/arch/arm/include/asm/arch-sunxi/dram.h
> index 0eccb1e6c28..59e2e980bfa 100644
> --- a/arch/arm/include/asm/arch-sunxi/dram.h
> +++ b/arch/arm/include/asm/arch-sunxi/dram.h
> @@ -45,5 +45,6 @@ unsigned long sunxi_dram_init(void);
>  void mctl_await_completion(u32 *reg, u32 mask, u32 val);
>  bool mctl_mem_matches(u32 offset);
>  bool mctl_mem_matches_base(u32 offset, ulong base);
> +bool mctl_check_memory(phys_addr_t addr);
>  
>  #endif /* _SUNXI_DRAM_H */
> diff --git a/arch/arm/mach-sunxi/dram_dw_helpers.c b/arch/arm/mach-sunxi/dram_dw_helpers.c
> index 24767354935..d2af2d57fde 100644
> --- a/arch/arm/mach-sunxi/dram_dw_helpers.c
> +++ b/arch/arm/mach-sunxi/dram_dw_helpers.c
> @@ -143,8 +143,28 @@ void mctl_auto_detect_dram_size(const struct dram_para *para,
>  
>  unsigned long mctl_calc_size(const struct dram_config *config)
>  {
> +	unsigned long size;
>  	u8 width = config->bus_full_width ? 4 : 2;
>  
>  	/* 8 banks */
> -	return (1ULL << (config->cols + config->rows + 3)) * width * config->ranks;
> +	size = (1ULL << (config->cols + config->rows + 3)) * width *
> +		config->ranks;
> +
> +	/*
> +	 * There are boards with non-power-of-2 sized DRAM chips, like 1.5GB
> +	 * or 3GB. They are detected as the larger power-of-2 (2GB and 4GB),
> +	 * so test the last quarter for being able to store values.
> +	 */
> +	if (!mctl_check_memory(CFG_SYS_SDRAM_BASE + size / 4 * 3)) {
> +		if (mctl_check_memory(CFG_SYS_SDRAM_BASE + size / 4 * 3 - 64)) {
> +			size = (size / 4) * 3;
> +			debug("capping memory at %ld MB\n", size >> 20);
> +		} else {
> +			printf("DRAM test failure at address 0x%lx\n",
> +			       CFG_SYS_SDRAM_BASE + size / 4 * 3 - 64);
> +			return 0;
> +		}
> +	}
> +
> +	return size;
>  }
> diff --git a/arch/arm/mach-sunxi/dram_helpers.c b/arch/arm/mach-sunxi/dram_helpers.c
> index 83dbe4ca98f..376b7d14f86 100644
> --- a/arch/arm/mach-sunxi/dram_helpers.c
> +++ b/arch/arm/mach-sunxi/dram_helpers.c
> @@ -62,3 +62,15 @@ bool mctl_mem_matches(u32 offset)
>  	return mctl_mem_matches_base(offset, CFG_SYS_SDRAM_BASE);
>  }
>  #endif
> +
> +bool mctl_check_memory(phys_addr_t addr)
> +{
> +	uint32_t orig, val;
> +
> +	orig = readl(addr);
> +	writel(~orig, addr);
> +	val = readl(addr);
> +	writel(orig, addr);
> +
> +	return ~orig == val;
> +}
>