Re: [Xen-devel] Problems when using latest git tree to boot xen on OMAP5

[Chen Baozi <baozich@xxxxxxxxx>]

On Oct 10, 2013, at 7:07 PM, Julien Grall <julien.grall@xxxxxxxxxx> wrote:

> On 10/10/2013 09:05 AM, Chen Baozi wrote:
>> On Wed, Oct 09, 2013 at 09:11:16AM +0100, Ian Campbell wrote:
>>> On Wed, 2013-10-09 at 15:46 +0800, Chen Baozi wrote:
>>>> On Mon, Oct 07, 2013 at 11:59:16AM +0100, Julien Grall wrote:
>>>>> On 10/07/2013 10:58 AM, Chen Baozi wrote:
>>>>>> On 10/07/2013 04:39 PM, Ian Campbell wrote:
>>>>>>> 
>>>>>>> It is certainly a bug in the kernel if it is accessing something which
>>>>>>> is disabled. It may also independently be a bug in the dts that this
>>>>>>> devices is disabled.
>>>>>>> 
>>>>>>> However in v3.12-rc4 I don't see mmc@480d1000 being disabled in
>>>>>>> omap5-uevm.dts and I can't see anything in the history of that file
>>>>>>> either. Where did your copy come from?
>>>>>> 
>>>>>> I'm currently working on the "omap5-v3.11-rc3" branch from
>>>>>> git://github.com/rogerq/linux.git, which contains a few necessary
>>>>>> platform patches not upstreamed. In omap5-uevm.dts, there are lines like:
>>>>>> 
>>>>>> 253 &mmc4 {
>>>>>> 254     status = "disabled";
>>>>>> 255 };
>>>>>> 256
>>>>>> 257 &mmc5 {
>>>>>> 258     status = "disabled";
>>>>>> 259 };
>>>>>> 
>>>>>> the mmc4 refers to mmc@480d1000, which defines at omap5.dtsi:
>>>>>> 
>>>>>> 417         mmc4: mmc@480d1000 {
>>>>>> 
>>>>>> I checked Linus' mainline git tree. It is the same about disabled mmc4
>>>>>> in omap5-uevm.dts. And the change is introduced in commit 5dd18b0 of the
>>>>>> mainline kernel.
>>>>>> 
>>>>>> Anyway, I'll see what exactly happened in the dom0 kernel dealing with
>>>>>> those "disabled" regions.
>>>>> 
>>>>> I looked at the Linux code. It will populate the different devices via
>>>>> the of_platform_populate (drivers/of/platform.c).
>>>>> 
>>>>> This function checks in of_platform_create_pdata if the device is
>>>>> available. So the mmc driver (driver/mmc/host/omap_hsmmc.c) should not
>>>>> be called for mmc4.
>>>> 
>>>> I've discuessed this issue on linux-omap@xxxxxxxxxxxxxxxx The TI guy says
>>>> that "DT disabled" means that device won't be created but hwmod bus
>>>> initially would try to initialize all supported modules by doing reset
>>>> access in their io memory address regions. That's why dom0 have accessed
>>>> mmc4 address even though it has been disabled.
>>> 
>>> ePAPR lists the option of "status = fail" which is "Indicates that the
>>> device is not operational. A serious error was detected in the device,
>>> and it is unlikely to become operational without repair." I'm not sure
>>> that is quite right though.
>>> 
>>> Rather than whitelisting and mapping disabled devices through perhaps we
>>> should implement them as read 0xf (or 0x0) and write ignore?
>>> 
>>> Or maybe we should just be mapping non-blacklisted disabled devices
>>> through to dom0, for it to use or ignore as it pleases. Julien, what was
>>> the reasoning here again?
>> 
>> If we just simple don't pass the disabled node in DT to the dom0, anything
>> inpropriate?
> 
> Few mails ago, you said there is hardcoded access in Linux for OMAP,
> right? I don't think removing the node from the Device Tree will change
> something with this problem.

Oh, I just had a assumption about hardcoded stuffs then. However, after 
discussed
with TI guys, it turns out I've just made a wrong assumption. There is no
hard-coding rather a different requirement why omap_hwmod accesses the module's
io memory space, according to their explanation. Sorry for not making it clear
when I got the new explanation.

Thanks.

Baozi
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