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Subject: Re: [PATCH v16 10/11] of: fdt: Add memory for devices by DT property
 "linux,usable-memory-range"
To:     Rob Herring <robh@kernel.org>
CC:     Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        <x86@kernel.org>, "H . Peter Anvin" <hpa@zytor.com>,
        <linux-kernel@vger.kernel.org>, Dave Young <dyoung@redhat.com>,
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        <devicetree@vger.kernel.org>, "Jonathan Corbet" <corbet@lwn.net>,
        <linux-doc@vger.kernel.org>, Randy Dunlap <rdunlap@infradead.org>,
        Feng Zhou <zhoufeng.zf@bytedance.com>,
        Kefeng Wang <wangkefeng.wang@huawei.com>,
        Chen Zhou <dingguo.cz@antgroup.com>
References: <20211123124646.1995-1-thunder.leizhen@huawei.com>
 <20211123124646.1995-11-thunder.leizhen@huawei.com>
 <YaaitPTArUZEriob@robh.at.kernel.org>
From:   "Leizhen (ThunderTown)" <thunder.leizhen@huawei.com>
Message-ID: <0dc664f7-65ae-767c-3fe6-d1bcf50d41e1@huawei.com>
Date:   Wed, 1 Dec 2021 10:55:46 +0800
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On 2021/12/1 6:16, Rob Herring wrote:
> On Tue, Nov 23, 2021 at 08:46:45PM +0800, Zhen Lei wrote:
>> From: Chen Zhou <chenzhou10@huawei.com>
>>
>> When reserving crashkernel in high memory, some low memory is reserved
>> for crash dump kernel devices and never mapped by the first kernel.
>> This memory range is advertised to crash dump kernel via DT property
>> under /chosen,
>>         linux,usable-memory-range = <BASE1 SIZE1 [BASE2 SIZE2]>
>>
>> We reused the DT property linux,usable-memory-range and made the low
>> memory region as the second range "BASE2 SIZE2", which keeps compatibility
>> with existing user-space and older kdump kernels.
>>
>> Crash dump kernel reads this property at boot time and call memblock_add()
>> to add the low memory region after memblock_cap_memory_range() has been
>> called.
>>
>> Signed-off-by: Chen Zhou <chenzhou10@huawei.com>
>> Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
>> ---
>>  drivers/of/fdt.c | 36 ++++++++++++++++++++++++++----------
>>  1 file changed, 26 insertions(+), 10 deletions(-)
>>
>> diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c
>> index 37b477a51175359..1ea2a0b1657e3a9 100644
>> --- a/drivers/of/fdt.c
>> +++ b/drivers/of/fdt.c
>> @@ -967,6 +967,15 @@ static void __init early_init_dt_check_for_elfcorehdr(unsigned long node)
>>  
>>  static unsigned long chosen_node_offset = -FDT_ERR_NOTFOUND;
>>  
>> +/*
>> + * The main usage of linux,usable-memory-range is for crash dump kernel.
>> + * Originally, the number of usable-memory regions is one. Now there may
>> + * be two regions, low region and high region.
>> + * To make compatibility with existing user-space and older kdump, the low
>> + * region is always the last range of linux,usable-memory-range if exist.
>> + */
>> +#define MAX_USABLE_RANGES		2
>> +
>>  /**
>>   * early_init_dt_check_for_usable_mem_range - Decode usable memory range
>>   * location from flat tree
>> @@ -974,10 +983,9 @@ static unsigned long chosen_node_offset = -FDT_ERR_NOTFOUND;
>>   */
>>  static void __init early_init_dt_check_for_usable_mem_range(unsigned long node)
>>  {
>> -	const __be32 *prop;
>> -	int len;
>> -	phys_addr_t cap_mem_addr;
>> -	phys_addr_t cap_mem_size;
>> +	struct memblock_region rgn[MAX_USABLE_RANGES] = {0};
>> +	const __be32 *prop, *endp;
>> +	int len, i = 0;
>>  
>>  	if ((long)node < 0)
>>  		return;
>> @@ -985,16 +993,24 @@ static void __init early_init_dt_check_for_usable_mem_range(unsigned long node)
>>  	pr_debug("Looking for usable-memory-range property... ");
>>  
>>  	prop = of_get_flat_dt_prop(node, "linux,usable-memory-range", &len);
>> -	if (!prop || (len < (dt_root_addr_cells + dt_root_size_cells)))
>> +	if (!prop)
> 
> if (!prop || (len % (dt_root_addr_cells + dt_root_size_cells)))

OK.

> 
>>  		return;
>>  
>> -	cap_mem_addr = dt_mem_next_cell(dt_root_addr_cells, &prop);
>> -	cap_mem_size = dt_mem_next_cell(dt_root_size_cells, &prop);
>> +	endp = prop + (len / sizeof(__be32));
>> +	while ((endp - prop) >= (dt_root_addr_cells + dt_root_size_cells)) {
> 
> for (i = 0; i < MAX_USABLE_RANGES, prop < endp; i++) {
> 
>> +		rgn[i].base = dt_mem_next_cell(dt_root_addr_cells, &prop);
>> +		rgn[i].size = dt_mem_next_cell(dt_root_size_cells, &prop);
>> +
>> +		pr_debug("cap_mem_regions[%d]: base=%pa, size=%pa\n",
>> +			 i, &rgn[i].base, &rgn[i].size);
>>  
>> -	pr_debug("cap_mem_start=%pa cap_mem_size=%pa\n", &cap_mem_addr,
>> -		 &cap_mem_size);
>> +		if (++i >= MAX_USABLE_RANGES)
>> +			break;
> 
> And drop this if.

OK.

> 
>> +	}
>>  
>> -	memblock_cap_memory_range(cap_mem_addr, cap_mem_size);
>> +	memblock_cap_memory_range(rgn[0].base, rgn[0].size);
>> +	for (i = 1; i < MAX_USABLE_RANGES && rgn[i].size; i++)
> 
> s/ &&/,/

Hi Rob:

The comma operator may not be suitable for logical judgment. The logical judgment
before commas (,) is ignored.

Here's my test：

C code：
int main()
{
        int i, j;

        printf("&&:\n");
        for (i = 0, j = 0; i < 2 && j < 3; i++, j++)
                printf("i=%d, j=%d\n", i, j);

        printf("\ncomma:\n");
        for (i = 0, j = 0; i < 2, j < 3; i++, j++)	//(i < 2） before comma is ignored
                printf("i=%d, j=%d\n", i, j);

        return 0;
}

Output：
&&:
i=0, j=0
i=1, j=1

comma:
i=0, j=0
i=1, j=1
i=2, j=2


> 
>> +		memblock_add(rgn[i].base, rgn[i].size);
>>  }
>>  
>>  #ifdef CONFIG_SERIAL_EARLYCON
>> -- 
>> 2.25.1
>>
>>
> 
> .
>