linux-kernel - Re: [RFC][PATCH] Kexec support for PPC440x

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Message-ID: <4E0ABA3F.5040809@in.ibm.com>
Date:	Wed, 29 Jun 2011 11:08:07 +0530
From:	Suzuki Poulose <suzuki@...ibm.com>
To:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
CC:	"kexec@...ts.infradead.org" <kexec@...ts.infradead.org>,
	linux ppc dev <linuxppc-dev@...ts.ozlabs.org>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: [RFC][PATCH] Kexec support for PPC440x

On 06/03/11 19:23, Sebastian Andrzej Siewior wrote:
> Suzuki Poulose wrote:
>>>> The way you setup the 1:1 mapping should be close to what you are doing on
>>>> kernel entry.Isn't it possible to include the file here and in the entry
>>>> code?
>>
>>> I will make this change and resend the patch.
>>
>> I took a look at the way we do it at kernel entry. It looks more cleaner to leave
>> it untouched. Especially, when we add the support for 47x in the future, the code
>> will become more unreadable.
>>
>> What do you think ?
>
> So the entry code has one 256MiB mapping, you need 8 of those. Entry goes for TLB 63 and you need to be flexible and avoid TLB 63 :).
> So after all you don't have that much in common with the entry code. If
> you look at the FSL-book code then you will notice that I tried to share
> some code.
>
> I don't understand why you don't flip the address space bit. On fsl we
> setup the tmp mapping in the "other address" space so we don't have two
> mappings for the same address. The entry code could be doing this with STS
> bit, I'm not sure.

I am not sure if I understood this correctly.
Could you explain how could there be two mappings for the same address ?
We are setting up 1:1 mapping for 0-2GiB and the only mapping that could exist
(in other words, not invalidated) is PAGE_OFFSET mapping. Since PAGE_OFFSET < 2GiB
we won't have multiple mappings. Or in other words we could limit KEXEC_*_MEMORY_LIMIT
to PAGE_OFFSET to make sure the crossing doesn't occur.

The kernel entry code sets up the mapping without a tmp mapping in 44x. i.e, it uses
the mapping setup by the firmware/boot loader.

Thanks
Suzuki
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