linux-kernel - Re: [RESENDING PATCH] powerpc/wii: properly disable use of BATs when requested.

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Message-ID: <20190117010509.GH22334@latitude>
Date:   Thu, 17 Jan 2019 02:05:09 +0100
From:   Jonathan Neuschäfer <j.neuschaefer@....net>
To:     Christophe Leroy <christophe.leroy@....fr>
Cc:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Jonathan Neuschafer <j.neuschaefer@....net>,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        stable@...r.kernel.org
Subject: Re: [RESENDING PATCH] powerpc/wii: properly disable use of BATs when
 requested.

Hi again,

On Tue, Jan 15, 2019 at 04:43:20PM +0000, Christophe Leroy wrote:
> 'nobats' kernel parameter or some options like CONFIG_DEBUG_PAGEALLOC
> deny the use of BATS for mapping memory.
> 
> This patch makes sure that the specific wii RAM mapping function
> takes it into account as well.
> 
> Fixes: de32400dd26e ("wii: use both mem1 and mem2 as ram")
> Cc: stable@...r.kernel.org
> Signed-off-by: Christophe Leroy <christophe.leroy@....fr>
> ---
[...]
>  	/* MEM2 64MB@...0000000 */
>  	delta = wii_hole_start + wii_hole_size;
> +	if (__map_without_bats)
> +		return delta;
> +

Nothing is visibly broken without this patch, even with
CONFIG_DEBUG_PAGEALLOC (tested on top of v5.0-rc2), but the patch still
looks correct.

I'd prefer the 'if' block to be before the whole delta/size calculation,
to make the code slightly more readable because the delta and size
calculations stay in one visual block. It doesn't need to happen after
delta is calculated.

tentatively,
Reviewed-by: Jonathan Neuschäfer <j.neuschaefer@....net>


Thanks,
Jonathan

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