linux-kernel - Re: [PATCH 1/2] riscv: Register System RAM as iomem resources

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Date:   Tue, 16 Jun 2020 14:51:53 +0300
From:   Nick Kossifidis <mick@....forth.gr>
To:     Zong Li <zong.li@...ive.com>
Cc:     paul.walmsley@...ive.com, palmer@...belt.com,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] riscv: Register System RAM as iomem resources

Στις 2020-06-16 10:45, Zong Li έγραψε:
> Add System RAM to /proc/iomem, various tools expect it such as kdump.
> It is also needed for page_is_ram API which checks the specified 
> address
> whether registered as System RAM in iomem_resource list.
> 
> Signed-off-by: Zong Li <zong.li@...ive.com>
> ---
>  arch/riscv/mm/init.c | 22 ++++++++++++++++++++++
>  1 file changed, 22 insertions(+)
> 
> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> index f4adb3684f3d..bbe816e03b2f 100644
> --- a/arch/riscv/mm/init.c
> +++ b/arch/riscv/mm/init.c
> @@ -517,6 +517,27 @@ void mark_rodata_ro(void)
>  }
>  #endif
> 
> +void __init resource_init(void)
> +{
> +	struct memblock_region *region;
> +
> +	for_each_memblock(memory, region) {
> +		struct resource *res;
> +
> +		res = memblock_alloc(sizeof(struct resource), SMP_CACHE_BYTES);
> +		if (!res)
> +			panic("%s: Failed to allocate %zu bytes\n", __func__,
> +			      sizeof(struct resource));
> +
> +		res->name = "System RAM";
> +		res->start = __pfn_to_phys(memblock_region_memory_base_pfn(region));
> +		res->end = __pfn_to_phys(memblock_region_memory_end_pfn(region)) - 
> 1;
> +		res->flags = IORESOURCE_SYSTEM_RAM | IORESOURCE_BUSY;
> +
> +		request_resource(&iomem_resource, res);
> +	}
> +}
> +
>  void __init paging_init(void)
>  {
>  	setup_vm_final();
> @@ -524,6 +545,7 @@ void __init paging_init(void)
>  	sparse_init();
>  	setup_zero_page();
>  	zone_sizes_init();
> +	resource_init();
>  }
> 
>  #ifdef CONFIG_SPARSEMEM_VMEMMAP


I already have a patch for registering System RAM as an iomem resource 
on my kexec/kdump series. Since I don't care about System RAM regions 
being accurately exposed to userspace (I parse the current device tree 
instead) I just use memblock_start_of_DRAM/end_of_DRAM. This approach 
from arm64 codebase is better since it also handles the case of sparse 
memory regions but in order to be useful for kdump we need to add the 
various segments of the kernel image as child nodes to their respective 
region for kexec-tools. I'll re-spin my patchset anyway so I'll extend 
it to better handle System RAM regions.