linux-kernel - Re: [PATCH v4 09/24] iommu/io-pgtable-arm-v7s: Clear LVL

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Date:   Thu, 26 Nov 2020 16:03:49 +0000
From:   Robin Murphy <robin.murphy@....com>
To:     Yong Wu <yong.wu@...iatek.com>, Joerg Roedel <joro@...tes.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Rob Herring <robh+dt@...nel.org>, Will Deacon <will@...nel.org>
Cc:     youlin.pei@...iatek.com, devicetree@...r.kernel.org,
        Nicolas Boichat <drinkcat@...omium.org>,
        srv_heupstream@...iatek.com, chao.hao@...iatek.com,
        kernel-team@...roid.com, linux-kernel@...r.kernel.org,
        Evan Green <evgreen@...omium.org>,
        Tomasz Figa <tfiga@...gle.com>,
        iommu@...ts.linux-foundation.org,
        linux-mediatek@...ts.infradead.org,
        Krzysztof Kozlowski <krzk@...nel.org>, anan.sun@...iatek.com,
        Greg Kroah-Hartman <gregkh@...gle.com>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v4 09/24] iommu/io-pgtable-arm-v7s: Clear LVL_SHIFT/BITS
 macro instead of the formula

On 2020-11-11 12:38, Yong Wu wrote:
> The current _ARM_V7S_LVL_BITS/ARM_V7S_LVL_SHIFT use a formula to calculate
> the corresponding value for level1 and level2 to pretend the code sane.
> Actually their level1 and level2 values are different from each other.
> This patch only clear the two macro. No functional change.

Grammar nit: to "clear" the macro sounds like you're making it empty or 
removing it entirely; I think you mean to say "clarify" here. English is 
the worst language sometimes... :)

Reviewed-by: Robin Murphy <robin.murphy@....com>

> Suggested-by: Robin Murphy <robin.murphy@....com>
> Signed-off-by: Yong Wu <yong.wu@...iatek.com>
> ---
>   drivers/iommu/io-pgtable-arm-v7s.c | 8 +++-----
>   1 file changed, 3 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/iommu/io-pgtable-arm-v7s.c b/drivers/iommu/io-pgtable-arm-v7s.c
> index 4d0aa079470f..58cc201c10a3 100644
> --- a/drivers/iommu/io-pgtable-arm-v7s.c
> +++ b/drivers/iommu/io-pgtable-arm-v7s.c
> @@ -44,13 +44,11 @@
>   
>   /*
>    * We have 32 bits total; 12 bits resolved at level 1, 8 bits at level 2,
> - * and 12 bits in a page. With some carefully-chosen coefficients we can
> - * hide the ugly inconsistencies behind these macros and at least let the
> - * rest of the code pretend to be somewhat sane.
> + * and 12 bits in a page.
>    */
>   #define ARM_V7S_ADDR_BITS		32
> -#define _ARM_V7S_LVL_BITS(lvl)		(16 - (lvl) * 4)
> -#define ARM_V7S_LVL_SHIFT(lvl)		(ARM_V7S_ADDR_BITS - (4 + 8 * (lvl)))
> +#define _ARM_V7S_LVL_BITS(lvl)		((lvl) == 1 ? 12 : 8)
> +#define ARM_V7S_LVL_SHIFT(lvl)		((lvl) == 1 ? 20 : 12)
>   #define ARM_V7S_TABLE_SHIFT		10
>   
>   #define ARM_V7S_PTES_PER_LVL(lvl)	(1 << _ARM_V7S_LVL_BITS(lvl))
>