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

[Zhang, Jonathan Zhixiong]

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@xxxxxxxxxxxxxx>
> >
> > 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
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/