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SubjectRe: [PATCH V4 1/4] efi: x86: rearrange efi_mem_attributes()

On 6/15/2015 10:09 AM, Matt Fleming wrote:
> On Fri, 12 Jun, at 06:01:44PM, Jonathan (Zhixiong) Zhang wrote:
>> From: "Jonathan (Zhixiong) Zhang" <zjzhang@codeaurora.org>
>>
>> x86 and ia64 implement efi_mem_attributes() differently. This
>> function needs to be available for other arch (such as arm64)
>> as well, such as for the purpose of ACPI/APEI.
>>
>> ia64 efi does not setup memmap variable and does not set
>> EFI_MEMMAP flag, so it needs to have its unique implementation
>> of efi_mem_attributes().
>
> Something like the above paragraph...
>
>> @@ -517,3 +517,21 @@ char * __init efi_md_typeattr_format(char *buf, size_t size,
>> attr & EFI_MEMORY_UC ? "UC" : "");
>> return buf;
>> }
>
> needs to go here, i.e. as documentation for efi_mem_atributes(). You
> need to explain why this function is marked as __weak at the function
> definition site.
>
>> +u64 __weak efi_mem_attributes(unsigned long phys_addr)
>> +{
>> + efi_memory_desc_t *md;
>> + void *p;
>> +
>> + if (!efi_enabled(EFI_MEMMAP))
>> + return 0;
>> +
>> + for (p = memmap.map; p < memmap.map_end; p += memmap.desc_size) {
>> + md = p;
>> + if ((md->phys_addr <= phys_addr) &&
>> + (phys_addr < (md->phys_addr +
>> + (md->num_pages << EFI_PAGE_SHIFT))))
>> + return md->attribute;
>> + }
>> + return 0;
>> +}
>
> because otherwise people are going to read this in the future and think,
>
> "efi_mem_attribute() doesn't quite work how I want it to for my arch,
> but it's __weak, so I'll override it"
>
> which is absolutely not the practice we should be promoting.
>
> How about something like this,
>
> /*
> * efi_mem_attributes - lookup memmap attributes for physical address
> * @phys_addr: the physical address to lookup
> *
> * Search in the EFI memory map for the region covering
> * @phys_addr. Returns the EFI memory attributes if the region
> * was found in the memory map, 0 otherwise.
> *
> * Despite being marked __weak most architectures should *not*
> * override this function. It is __weak solely for the benefit
> * of ia64 which has a funky EFI memory map that doesn't work
> * the same way as other architectures.
> */
>
Thank you Matt for the suggestion. Will do so accordingly.

--
Jonathan (Zhixiong) Zhang
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
a Linux Foundation Collaborative Project


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