linux-kernel - Re: [PATCH 2/2] powerpc/83xx: map IMMR with a BAT.

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Message-ID: <b201df6242e7f6cebd525e0a301eef2afdb38f30.camel@buserror.net>
Date:   Sat, 14 Sep 2019 09:34:44 -0500
From:   Scott Wood <oss@...error.net>
To:     Christophe Leroy <christophe.leroy@....fr>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        galak@...nel.crashing.org
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH 2/2] powerpc/83xx: map IMMR with a BAT.

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@....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...

-Scott