Platform data with function pointers

[Eric Miao]

On Fri, Jun 18, 2010 at 10:25 PM, Lorenzo Pieralisi
<Lorenzo.Pieralisi at arm.com> wrote:
> Concerning platform_devices ids, sorry I wasn't meant to report an amba primecell binding snippet, I wanted to report here just a
> binding for a simple memory mapped platform device (not a primecell one). I was asking that question about platform_device
> statically defined structs that use the id for enumeration, and going with FDT the id has to be initialized somehow from the tree
> because the struct is allocated dynamically.
>
> Wrt map_desc point taken, I was looking into possible ways of getting rid of platform specific statically defined data, that array
> in particular.
>

That's actually quite challenging. And as DT is used to 'describe' the hardware
as is, instead of directing the software how to do a mapping, I doubt
this should
be done with DT.

> Thanks a lot for your feedback,
>
> Lorenzo
>
> -----Original Message-----
> From: Russell King - ARM Linux [mailto:linux at arm.linux.org.uk]
> Sent: Friday, June 18, 2010 2:13 PM
> To: Lorenzo Pieralisi
> Cc: 'Grant Likely'; devicetree-discuss; linux-arm-kernel at lists.infradead.org; Jeremy Kerr; Nicolas Pitre
> Subject: Re: Platform data with function pointers
>
> On Fri, Jun 18, 2010 at 01:47:28PM +0100, Lorenzo Pieralisi wrote:
>> I think chip-select addressing should be used if that is the way HW handles it. If the device is described through a
> memory-mapping,
>> ex. snippet follows:
>>
>> serial at 101f2000 {
>>         compatible = "arm,pl011";
>>         reg = <0x101f2000 0x1000 >;
>> };
>
> Primecell devices aren't platform devices.  They have no 'id' field as
> such.  Instead, modern implementations have PCI-like IDs.
>
>> struct map_desc {
>>       unsigned long virtual;
>>       unsigned long pfn;
>>       unsigned long length;
>>       unsigned int type;
>> };
>>
>> static struct map_desc realview_eb_io_desc[] __initdata = {
>>       {
>>               .virtual        = IO_ADDRESS(REALVIEW_SYS_BASE),
>>               .pfn            = __phys_to_pfn(REALVIEW_SYS_BASE),
>>               .length         = SZ_4K,
>>               .type           = MT_DEVICE,
>>       }, ...
>
> These mappings are entirely arbitary, and change according to the
> implementation of the platform.
>
> Some platforms want to avoid using ioremap() to create 4K page mappings
> for their devices, so instead they statically map them and arrange for
> ioremap() to know about that static mapping.
>
> Given that PAGE_OFFSET can be changed, it would be absolutely silly to
> put this into the device tree.
>
>
>
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