[U-Boot] [PATCH] dm: core: Add platform specific bus translation function

Stefan Roese
2015-12-02T14:11:21Z

Hi Simon,

On 01.12.2015 21:02, Simon Glass wrote:
> Hi Stefan,
>
> On 30 November 2015 at 23:05, Stefan Roese <sr@denx.de> wrote:
>> Hi Simon,
>>
>>
>> On 01.12.2015 00:17, Simon Glass wrote:
>>>
>>> Hi Stefan,
>>>
>>> On 29 November 2015 at 23:52, Stefan Roese <sr@denx.de> wrote:
>>>>
>>>> Hi Simon,
>>>>
>>>> On 27.11.2015 19:36, Simon Glass wrote:
>>>>>
>>>>> On 27 November 2015 at 02:22, Stefan Roese <sr@denx.de> wrote:
>>>>>>
>>>>>> This patch adds the additional platform_translate_address() call to
>>>>>> dev_get_addr(). A weak default with a 1-to-1 translation is also
>>>>>> provided. Platforms that need a special address translation can
>>>>>> overwrite this function.
>>>>>>
>>>>>> Here the explanation, why this is needed for MVEBU:
>>>>>>
>>>>>> When using DM with DT address translation, this does not work
>>>>>> with the standard fdt_translate_address() function on MVEBU
>>>>>> in SPL. Since the DT translates to the 0xf100.0000 base
>>>>>> address for the internal registers. But SPL still has the
>>>>>> registers mapped to the 0xd000.0000 (SOC_REGS_PHY_BASE)
>>>>>> address that is used by the BootROM. This is because SPL
>>>>>> may return to the BootROM for boot continuation (e.g. UART
>>>>>> xmodem boot mode).
>>>>>>
>>>>>> Signed-off-by: Stefan Roese <sr@denx.de>
>>>>>> Cc: Simon Glass <sjg@chromium.org>
>>>>>> Cc: Luka Perkov <luka.perkov@sartura.hr>
>>>>>> Cc: Dirk Eibach <dirk.eibach@gdsys.cc>
>>>>>> ---
>>>>>> drivers/core/device.c | 36 +++++++++++++++++++++++++-----------
>>>>>> 1 file changed, 25 insertions(+), 11 deletions(-)
>>>>>
>>>>>
>>>>> I wonder if there is a way to handle this with device tree? I would
>>>>> very much like to avoid adding weak functions and other types of
>>>>> hooks.
>>>>
>>>>
>>>> I've thought about this also for quite a bit. But couldn't come
>>>> up with a "better", less intrusive implementation for this
>>>> problem yet.
>>>>
>>>>> Are you saying that there are two values for 'ranges', one in
>>>>> SPL and one for U-Boot proper?
>>>>
>>>>
>>>> You can think of it as 2 values for "ranges", yes. Basically
>>>> its a difference in the upper 8 bits of all addresses of the
>>>> internal registers (e.g. UART, SDRAM controller...).
>>>>
>>>> The BootROM starts with 0xd000.0000 and SPL also needs to
>>>> use this value. As SPL returns back into the BootROM in
>>>> some cases. And Linux (and other OS'es) expect 0xf100.0000
>>>> as base address. So the main U-Boot reconfigured the base
>>>> address to this value quite early.
>>>>
>>>>> What actually triggers the change?
>>>>
>>>>
>>>> This is no change. Its just, that now SPL has added DM and DTS
>>>> support. Before this SPL-DM support this was handled by
>>>> something like this:
>>>>
>>>> #if defined(CONFIG_SPL_BUILD)
>>>> #define SOC_REGS_PHY_BASE 0xd0000000
>>>> #else
>>>> #define SOC_REGS_PHY_BASE 0xf1000000
>>>> #endif
>>>> #define MVEBU_REGISTER(x) (SOC_REGS_PHY_BASE + x)
>>>> #define MVEBU_SDRAM_SCRATCH (MVEBU_REGISTER(0x01504))
>>>> #define MVEBU_L2_CACHE_BASE (MVEBU_REGISTER(0x08000))
>>>> ...
>>>>
>>>> And now (nearly) all addresses are taken from the DT. And the
>>>> SPL vs. U-Boot proper base address difference needs to get
>>>> handled otherwise - here in the DT.
>>>
>>>
>>> No, I mean what causes the hardware address to move? Is there a
>>> register somewhere that it adjusted to tell the addressing to change?
>>
>>
>> Yes. U-Boot proper reconfigures this base address. Quite early
>> in arch_cpu_init(). Note that this change / configuration can't
>> be detected. So you have to know, where the internal registers
>> are mapped.
>>
>>>>
>>>>> One option would be to have a ranges-spl property, or similar.
>>>>
>>>>
>>>> Hmmm. you mean to add these "ranges-spl" properties additionally
>>>> to the normal "ranges" properties? I would really like to not
>>>> change the "ranges" in the dts files. As especially in the
>>>> MVEBU cases (Armada XP / 38x etc), the occurrences are very
>>>> high. And this would result in quite a big difference to the
>>>> "mainline Linux dts" version.
>>>
>>>
>>> Yes I mean a new property. After all, the existing one is incorrect
>>> for your hardware at least in some configuration.
>>>
>>>>
>>>> I could also add this functionality via a new Kconfig option.
>>>> Like this:
>>>>
>>>> + if (CONFIG_IS_ENABLED(PLATFORM_TRANSLATE_ADDRESS)) {
>>>> + addr = platform_translate_address((void *)gd->fdt_blob,
>>>> + dev->of_offset, addr);
>>>> + }
>>>>
>>>> So no weak default would be needed. Just let me know if you
>>>> would prefer it this way. And I'll send a v2 using this
>>>> approach.
>>>
>>>
>>> I'd like to exhaust the DT option first, as this adds another level of
>>> complexity...the DT is supposed to describe the hardware.
>>
>>
>> I understand. But your suggestion of a new "ranges-spl" property
>> would result in changes to the dts files (for all MVEBU boards)
>> and additional support for this "ranges-spl" property in the
>> U-Boot code. This looks more complex than the 2 lines to the
>> common code I suggested above. And definitely easier to maintain.
>> As new MVEBU boards would always have to patch their dts files
>> for U-Boot.
>
> But from another perspective, the dts file is clearly wrong IMO - it
> does not describe the memory of the system fully. It is only accurate
> once you 'flip the bit' to change the address space.
>
> This creates a callback to board-specific code. That's something I'm
> really trying to avoid with driver model. We should not have drivers
> calling into board code for things.
>
> Other options, none of which I am recommending, just trying to
> suggestion options we can discuss:
>
> - Describe the mapping somewhere else - e.g. in a /config node
> property like 'u-boot,range-offset'

I've started with a test version for this alternative. But this
also seems a bit clumsy, as I now need to conditionally use
this 'u-boot,range-offset' in get_dev_addr() - depending on
CONFIG_SPL_BUILD.

> - Add some sort of 'core' driver model address translation setting,
> which your board code can set up with a function call, and
> dev_get_addr() uses
> - Add a uclass and driver for address translation, and call it from
> here (ugh...)

All this doesn't sound very "promising". At least not to me. But
I had another idea, which might be a good alternative. Use a new,
different dts for SPL. This has most likely been discussed before,
not sure. The idea here is, to re-use the existing dts and include
it in the new dts. Something like:

U-Boot proper: armada-xp-gp.dts
SPL U-Boot: armada-xp-gp-spl.dts

And this new SPL dts includes the original dts and only changes
what needs to get changed for SPL. This could include all the
"u-boot,dm-pre-reloc" properties as well and look like this:

---<-----------------------
/*
* Device Tree file for Marvell Armada XP development board
* (DB-MV784MP-GP)
*/

#include "armada-xp-gp.dts"

/ {
soc {
/*
* Use 0xd0000000 as base address for the internal registers
* in SPL U-Boot
*/
ranges = <MBUS_ID(0xf0, 0x01) 0 0 0xd0000000 0x100000
MBUS_ID(0x01, 0x1d) 0 0 0xfff00000 0x100000
MBUS_ID(0x01, 0x2f) 0 0 0xf0000000 0x1000000>;
u-boot,dm-pre-reloc;

internal-regs {
u-boot,dm-pre-reloc;

serial at 12000 {
u-boot,dm-pre-reloc;
};
};
};
};
---<-----------------------

Unfortunately this approach does not work right now. The dtc
seems to not overlay the new values in the resulting dtb.

But has this approach been discussed before? Or if not, what do
you think of it (if and once it really works)?

Thanks,
Stefan