Subject: [PATCH 04/10] arm: zynq: Load scu baseaddress at run time

From: [email-masked] (Rob Herring)
Date: Tue, 26 Mar 2013 07:28:09 -0500

On 03/26/2013 05:45 AM, Michal Simek wrote:
> On 03/25/2013 11:34 PM, Rob Herring wrote:
>> On 03/25/2013 11:07 AM, Michal Simek wrote:
>>> 2013/3/25 Rob Herring <[email-masked]>:
>>>> On 03/25/2013 09:51 AM, Michal Simek wrote:
>>>>> Hi Rob,
>>>>>
>>>>> 2013/3/25 Rob Herring <[email-masked]>:
>>>>>> On 03/25/2013 08:53 AM, Michal Simek wrote:
>>>>>>> Use Cortex a9 cp15 to read scu baseaddress.
>>>>
>>>> [...]
>>>>
>>>>>>> +static void __init scu_init(void)
>>>>>>> +{
>>>>>>> +     unsigned long base;
>>>>>>> +
>>>>>>> +     base = scu_a9_get_base();
>>>>>>> +     zynq_cortex_a9_scu_map.pfn = __phys_to_pfn(base);
>>>>>>> +     zynq_cortex_a9_scu_map.virtual = base;
>>>>>>
>>>>>> You are setting the virtual address to the physical base?
>>>>>>
>>>>>>> +     iotable_init(&zynq_cortex_a9_scu_map, 1);
>>>>>>
>>>>>> Then creating a static mapping...
>>>>>>
>>>>>>> +     scu_base = ioremap(base, zynq_cortex_a9_scu_map.length);
>>>>>>
>>>>>> And also a dynamic mapping?
>>>>>
>>>>> Yes - exactly.
>>>>
>>>> You are simply getting lucky that it works. If the physical address did
>>>> not happen to be in the vmalloc address region, it would not work. You
>>>> should not do this because you have an implicit requirement and the
>>>> code
>>>> will look broken to anyone that reads it.
>>>
>>> yeah correct. I will add there a comment to mentioned that.
>>
>> I think leaving the define would be better, but either way is fine.
> 
> ok. From my point of view is better to keep scu where it is and any
> early vmalloc
> allocator will be really helpful. Because there is also early map
> for early console where virtual addresses are hardcoded.
> It will be just easier to ask generic code to return base if if you request
> for size.
> 
> static unsigned long iomapstart = VMALLOC_END;
> 
> unsigned long get_iomap_virtbase(unsigned long size)
> {
>     iomapstart -= size;
>     return iomapstart;
> }

It wouldn't be so simple with page/section alignment requirements and such.

> Something like this will be helpful and then instead of setup virtual
> addresses for every static io mapping just to call this function
> and you will get mapping correct all the time.

If you use DT for core count, then you don't need the static mapping and
can use ioremap (or of_iomap).

Rob