Re: [PATCH v3] pstore: Add mem_type property DT parsing support

[Mukesh Ojha]

Hi Kees/All,

Could you please review again?  I have addressed your comment made on 
last patch version.

Thanks,
Mukesh

On 3/23/2021 12:12 AM, Mukesh Ojha wrote:
> There could be a scenario where we define some region
> in normal memory and use them store to logs which is later
> retrieved by bootloader during warm reset.
>
> In this scenario, we wanted to treat this memory as normal
> cacheable memory instead of default behaviour which
> is an overhead. Making it cacheable could improve
> performance.
>
> This commit gives control to change mem_type from Device
> tree, and also documents the value for normal memory.
>
> Signed-off-by: Mukesh Ojha <mojha@xxxxxxxxxxxxxx>
> ---
> Changes in v3:
>   - Minor code and documentation update done as per comment given by Kees.
>
> Changes in v2:
>   - if-else converted to switch case
>   - updated MODULE_PARM_DESC with new memory type.
>   - default setting is still intact.
>
>   Documentation/admin-guide/ramoops.rst                  |  4 +++-
>   .../devicetree/bindings/reserved-memory/ramoops.txt    | 10 ++++++++--
>   fs/pstore/ram.c                                        |  7 ++++++-
>   fs/pstore/ram_core.c                                   | 18 ++++++++++++++++--
>   4 files changed, 33 insertions(+), 6 deletions(-)
>
> diff --git a/Documentation/admin-guide/ramoops.rst b/Documentation/admin-guide/ramoops.rst
> index b0a1ae7..8f107d8 100644
> --- a/Documentation/admin-guide/ramoops.rst
> +++ b/Documentation/admin-guide/ramoops.rst
> @@ -3,7 +3,7 @@ Ramoops oops/panic logger
>   
>   Sergiu Iordache <sergiu@xxxxxxxxxxxx>
>   
> -Updated: 17 November 2011
> +Updated: 10 Feb 2021
>   
>   Introduction
>   ------------
> @@ -30,6 +30,8 @@ mapping to pgprot_writecombine. Setting ``mem_type=1`` attempts to use
>   depends on atomic operations. At least on ARM, pgprot_noncached causes the
>   memory to be mapped strongly ordered, and atomic operations on strongly ordered
>   memory are implementation defined, and won't work on many ARMs such as omaps.
> +Setting ``mem_type=2`` attempts to treat the memory region as normal memory,
> +which enables full cache on it. This can improve the performance.
>   
>   The memory area is divided into ``record_size`` chunks (also rounded down to
>   power of two) and each kmesg dump writes a ``record_size`` chunk of
> diff --git a/Documentation/devicetree/bindings/reserved-memory/ramoops.txt b/Documentation/devicetree/bindings/reserved-memory/ramoops.txt
> index b7886fe..6f1cb20 100644
> --- a/Documentation/devicetree/bindings/reserved-memory/ramoops.txt
> +++ b/Documentation/devicetree/bindings/reserved-memory/ramoops.txt
> @@ -42,8 +42,14 @@ Optional properties:
>   - pmsg-size: size in bytes of log buffer reserved for userspace messages
>     (defaults to 0: disabled)
>   
> -- unbuffered: if present, use unbuffered mappings to map the reserved region
> -  (defaults to buffered mappings)
> +- mem-type: if present, sets the type of mapping is to be used to map the
> +  reserved region. mem-type: 0 = write-combined (default), 1 = unbuffered,
> +  2 = cached.
> +
> +- unbuffered: deprecated, use mem_type instead. if present, and mem_type is
> +  not specified, it is equivalent to mem_type = 1 and uses unbuffered mappings
> +  to map the reserved region (defaults to buffered mappings mem_type = 0). If
> +  both are specified -- "mem_type" overrides "unbuffered".
>   
>   - max-reason: if present, sets maximum type of kmsg dump reasons to store
>     (defaults to 2: log Oopses and Panics). This can be set to INT_MAX to
> diff --git a/fs/pstore/ram.c b/fs/pstore/ram.c
> index ca6d8a8..fefe3d3 100644
> --- a/fs/pstore/ram.c
> +++ b/fs/pstore/ram.c
> @@ -56,7 +56,7 @@ MODULE_PARM_DESC(mem_size,
>   static unsigned int mem_type;
>   module_param(mem_type, uint, 0400);
>   MODULE_PARM_DESC(mem_type,
> -		"set to 1 to try to use unbuffered memory (default 0)");
> +		"memory type: 0=write-combined (default), 1=unbuffered, 2=cached");
>   
>   static int ramoops_max_reason = -1;
>   module_param_named(max_reason, ramoops_max_reason, int, 0400);
> @@ -648,6 +648,10 @@ static int ramoops_parse_dt(struct platform_device *pdev,
>   
>   	pdata->mem_size = resource_size(res);
>   	pdata->mem_address = res->start;
> +	/*
> +	 * Setting "unbuffered" is deprecated and will be ignored if
> +	 * "mem_type" is also specified.
> +	 */
>   	pdata->mem_type = of_property_read_bool(of_node, "unbuffered");
>   	/*
>   	 * Setting "no-dump-oops" is deprecated and will be ignored if
> @@ -666,6 +670,7 @@ static int ramoops_parse_dt(struct platform_device *pdev,
>   		field = value;						\
>   	}
>   
> +	parse_u32("mem-type", pdata->record_size, pdata->mem_type);
>   	parse_u32("record-size", pdata->record_size, 0);
>   	parse_u32("console-size", pdata->console_size, 0);
>   	parse_u32("ftrace-size", pdata->ftrace_size, 0);
> diff --git a/fs/pstore/ram_core.c b/fs/pstore/ram_core.c
> index fff363b..fe53050 100644
> --- a/fs/pstore/ram_core.c
> +++ b/fs/pstore/ram_core.c
> @@ -396,6 +396,10 @@ void persistent_ram_zap(struct persistent_ram_zone *prz)
>   	persistent_ram_update_header_ecc(prz);
>   }
>   
> +#define MEM_TYPE_WCOMBINE	0
> +#define MEM_TYPE_NONCACHED	1
> +#define MEM_TYPE_NORMAL		2
> +
>   static void *persistent_ram_vmap(phys_addr_t start, size_t size,
>   		unsigned int memtype)
>   {
> @@ -409,10 +413,20 @@ static void *persistent_ram_vmap(phys_addr_t start, size_t size,
>   	page_start = start - offset_in_page(start);
>   	page_count = DIV_ROUND_UP(size + offset_in_page(start), PAGE_SIZE);
>   
> -	if (memtype)
> +	switch (memtype) {
> +	case MEM_TYPE_NORMAL:
> +		prot = PAGE_KERNEL;
> +		break;
> +	case MEM_TYPE_NONCACHED:
>   		prot = pgprot_noncached(PAGE_KERNEL);
> -	else
> +		break;
> +	case MEM_TYPE_WCOMBINE:
>   		prot = pgprot_writecombine(PAGE_KERNEL);
> +		break;
> +	default:
> +		pr_err("invalid mem_type=%d\n", memtype);
> +		return NULL;
> +	}
>   
>   	pages = kmalloc_array(page_count, sizeof(struct page *), GFP_KERNEL);
>   	if (!pages) {