Re: [PATCH RFC] arm64/mm: handle memmap kernel option

[Yisheng Xie]

hi Mark,

Thanks for comment
On 2017/2/27 16:48, Mark Rutland wrote:
> Hi,
> 
> On Mon, Feb 27, 2017 at 11:48:50AM +0800, Yisheng Xie wrote:
>> On 2017/2/26 18:46, Ard Biesheuvel wrote:
>>> On 25 February 2017 at 06:47, Yisheng Xie <xieyisheng1@xxxxxxxxxx> wrote:
> 
>>>> To make user reserve memory for some specific use more convenient,
>>>> this patch implement the following memmap variants:
>>>>  - memmap=nn[KMG]$ss[KMG]: mark specified memory as reserved;
>>>>  - memmap=nn[KMG]@ss[KMG]: force usage of a specific region of memory;
> 
>>> Could you explain which problem you are solving here? ACPI implies
>>> UEFI on arm64, and so these reservations could be made by a boot
>>> component instead, if it requires a fixed memory reservation. If this
>>> is a reservation for, e.g., OP-TEE, we should not rely on the command
>>> line to communicate this information.
>>>
>> We just want to reserve some memory for a driver and I just not so familiar
>> with how to reserve memory with UEFI. So doubt about whether it is suitable
>> to reserve memory with cmdline like "memmap=xxx", which had appeared in x86
>> for a long time.
> 
> Could you please explain for what purpose this is necessary?
> 
> Does the driver need a specific region of memory? Or just some contiguous
> region? Or something else?
> 
Yes, we want to use a specific region of memory.

> For the former, this is not an appropriate solution; firmware must absolutely
> mark the memory as reserved for a particular purpose.
> 
I see, so just forget about this patch. sorry for disturbing.

Thanks again for your explain.
Yisheng Xie

> If you just need contiguous physical memory, I believe it would be better to
> use CMA, and request CMA reserve a larger area if necessary.
> 



> Thanks,
> Mark.
> 
> .
>