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Subject: Re: [PATCH 2/2] powerpc/83xx: map IMMR with a BAT.
To:     Scott Wood <oss@buserror.net>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Michael Ellerman <mpe@ellerman.id.au>,
        galak@kernel.crashing.org
Cc:     linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org
References: <b51b96090138aba1920d2cf7c0e0e348667f9a69.1566564560.git.christophe.leroy@c-s.fr>
 <331759c1bcba5797d30f8eace74afb16ac5f3c36.1566564560.git.christophe.leroy@c-s.fr>
 <b201df6242e7f6cebd525e0a301eef2afdb38f30.camel@buserror.net>
From:   Christophe Leroy <christophe.leroy@c-s.fr>
Message-ID: <e9437d8c-564e-cc76-e8fd-54e4000c2349@c-s.fr>
Date:   Sat, 14 Sep 2019 18:51:14 +0200
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Le 14/09/2019 à 16:34, Scott Wood a écrit :
> On Fri, 2019-08-23 at 12:50 +0000, Christophe Leroy wrote:
>> On mpc83xx with a QE, IMMR is 2Mbytes.
>> On mpc83xx without a QE, IMMR is 1Mbytes.
>> Each driver will map a part of it to access the registers it needs.
>> Some driver will map the same part of IMMR as other drivers.
>>
>> In order to reduce TLB misses, map the full IMMR with a BAT.
>>
>> Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
>> ---
>>   arch/powerpc/platforms/83xx/misc.c | 10 ++++++++++
>>   1 file changed, 10 insertions(+)
>>
>> diff --git a/arch/powerpc/platforms/83xx/misc.c
>> b/arch/powerpc/platforms/83xx/misc.c
>> index f46d7bf3b140..1e395b01c535 100644
>> --- a/arch/powerpc/platforms/83xx/misc.c
>> +++ b/arch/powerpc/platforms/83xx/misc.c
>> @@ -18,6 +18,8 @@
>>   #include <sysdev/fsl_soc.h>
>>   #include <sysdev/fsl_pci.h>
>>   
>> +#include <mm/mmu_decl.h>
>> +
>>   #include "mpc83xx.h"
>>   
>>   static __be32 __iomem *restart_reg_base;
>> @@ -145,6 +147,14 @@ void __init mpc83xx_setup_arch(void)
>>   	if (ppc_md.progress)
>>   		ppc_md.progress("mpc83xx_setup_arch()", 0);
>>   
>> +	if (!__map_without_bats) {
>> +		int immrsize = IS_ENABLED(CONFIG_QUICC_ENGINE) ? SZ_2M :
>> SZ_1M;
> 
> Any reason not to unconditionally make it 2M?  After all, the kernel being
> built with CONFIG_QUICC_ENGINE doesn't mean that the hardware you're running
> on has it...
> 

Euh .. ok. I didn't see it that way, but you are right.

Do you think it is not a problem to map 2M even when the quicc engine is 
not there ? Or should it check device tree instead ?

Christophe