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Subject: Re: [PATCH] powerpc: Enable kernel XZ compression option on PPC_85xx
To:     Michael Ellerman <mpe@ellerman.id.au>,
        Daniel Axtens <dja@axtens.net>,
        Pawel Dembicki <paweldembicki@gmail.com>
Cc:     Christian Lamparter <chunkeey@gmail.com>,
        linux-kernel@vger.kernel.org, Paul Mackerras <paulus@samba.org>,
        linuxppc-dev@lists.ozlabs.org
References: <20190603164115.27471-1-paweldembicki@gmail.com>
 <877e9qp3ou.fsf@dja-thinkpad.axtens.net>
 <87ftodempa.fsf@concordia.ellerman.id.au>
From:   Christophe Leroy <christophe.leroy@c-s.fr>
Message-ID: <f988951c-3077-ab19-81eb-560418468d14@c-s.fr>
Date:   Fri, 14 Jun 2019 12:06:48 +0200
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Le 13/06/2019 à 13:42, Michael Ellerman a écrit :
> Daniel Axtens <dja@axtens.net> writes:
>> Pawel Dembicki <paweldembicki@gmail.com> writes:
>>
>>> Enable kernel XZ compression option on PPC_85xx. Tested with
>>> simpleImage on TP-Link TL-WDR4900 (Freescale P1014 processor).
>>>
>>> Suggested-by: Christian Lamparter <chunkeey@gmail.com>
>>> Signed-off-by: Pawel Dembicki <paweldembicki@gmail.com>
>>> ---
>>>   arch/powerpc/Kconfig | 2 +-
>>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
>>> index 8c1c636308c8..daf4cb968922 100644
>>> --- a/arch/powerpc/Kconfig
>>> +++ b/arch/powerpc/Kconfig
>>> @@ -196,7 +196,7 @@ config PPC
>>>   	select HAVE_IOREMAP_PROT
>>>   	select HAVE_IRQ_EXIT_ON_IRQ_STACK
>>>   	select HAVE_KERNEL_GZIP
>>> -	select HAVE_KERNEL_XZ			if PPC_BOOK3S || 44x
>>> +	select HAVE_KERNEL_XZ			if PPC_BOOK3S || 44x || PPC_85xx
>>
>> (I'm not super well versed in the compression stuff, so apologies if
>> this is a dumb question.) If it's this simple, is there any reason we
>> can't turn it on generally, or convert it to a blacklist of platforms
>> known not to work?
> 
> For some platforms enabling XZ requires that your u-boot has XZ support,
> and I'm not very clear on when that support landed in u-boot and what
> boards have it. And there are boards out there with old/custom u-boots
> that effectively can't be updated.

I don't think that it has anything to do with u-boot.
AFAIK, today's mainline U-boot only supports GZIP (by default) and the 
following optional ones: LZO, LZMA, LZ4.

If we want to set additional compression types for u-boot, it is not 
enough to select HAVE_KERNEL_XXXX, we also have to update uImage 
generation scripts.

See the series I sent some time ago: 
https://patchwork.ozlabs.org/project/linuxppc-dev/list/?series=104153
I'll resent it without bzip2 as today's uboot doesn't support bzip2 anymore.

> 
> But as a server guy I don't really know the details of all that very
> well. So if someone tells me that we should enable XZ for everything, or
> as you say just black list some platforms, then that's fine by me.
> 

I guess we first need to understand how this is used.

Christophe