On 08/28/2012 07:08 PM, Arun Kumar K wrote:
> Hi Karol,
> Thanks for your comments.
> Please find my response inline.
Hi... and sorry for so much delayed response.
>>> +
>>> +static void __init exynos5_reserve(void)
>>> +{
>>> + s5p_mfc_reserve_mem(0x43000000, 8 << 20, 0x51000000, 8 << 20);
>>
>>
>> I think it would make sense to make this memory reservation dependent
>> on "mfc*" node being present in DTS. It's to early to use of_* functions
>> (because tree is not populated at this stage) but fdt_* family of functions
>> work just fine.
>>
>
> As I can see the fdt_* functions are not used in any of the ARM based SoC
> init codes. Though I can see some references in powerpc.
> The implementation and includes are present in arch/arm/boot/compressed/
> which I think cannot be used directly in mach-exynos unless we make some
> comon makefile changes.
It looks like I was writing from memory, and I actually mixed things
up. To be clear this time - we can't use regular device tree handling
functions in reserve() as it's too early. Namely, flattened device tree
is not yet converted to kernel's-natural representation. However,
I think we can scan fdt just fine. To do so one just needs to use
functions declared here
#include <linux/of_fdt.h>
Actual architecture-independent code is in drivers/of/fdt.c. This
provides of_fdt_ family of functions. Please see below for example.
> Please clarify whether its ok to use fdt_* functions to parse the dts in
> exynos machine init or please point me to some sample implementations
> which I can refer to.
It should be ok to use anything that works on flattened device tree
rather than its uncompressed version. I've experimented a bit and
something like this worked for me just fine (it was around 3.3-kernel
timeframe, but I don't think that fdt api has changed):
[mach-exynos4-dt.c]
#include <linux/of_fdt.h>
int fdt_find_compat(unsigned long node, const char *uname, int depth, void *data)
{
if (of_flat_dt_is_compatible(node, (char *)data))
return 1;
return 0;
}
static void __init exynos4210_dt_reserve(void)
{
/* Reserve memory for MFC only if it's available */
if (of_scan_flat_dt(fdt_find_compat, "samsung,s5pv210-mfc")) {
printk(KERN_NOTICE "exynos4-dt: mfc device node found - setting up memory area for dma\n");
s5p_mfc_reserve_mem(0x43000000, 8 << 20, 0x51000000, 8 << 20);
}
}
[.dts]
codec@some-addr {
compatible = "samsung,s5pv210-mfc";
};
So, in above code fragment I just check if mfc was defined in dts.
This could probably stay as it is.
Then I allocate _predefined_ region - and this part should be fixed.
If you have nodes like "mfc-r-size"/offset, then you could just get
this information directly from (f)dt rather than hardcoding it in the code.
Precisely, after we find compatible node we could do something like
following (untested):
unsigned long lsize, loff, rsize, roff len;
__be32 *prop;
prop = of_get_flat_dt_prop(node, "samsung,mfc-l-size", &len);
if (!prop)
return;
lsize = of_read_ulong(prop, len/4);
...
Regards,
--
Karol Lewandowski | Samsung Poland R&D Center | Linux/Platform
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