linux-kernel - Re: [PATCH v2 2/3] iommu/mediatek: add support for 6-bit encoded port IDs

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Date:   Tue, 4 Oct 2022 13:59:04 +0200
From:   AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>
To:     Alexandre Mergnat <amergnat@...libre.com>,
        Rob Herring <robh+dt@...nel.org>,
        Yong Wu <yong.wu@...iatek.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Will Deacon <will@...nel.org>, Joerg Roedel <joro@...tes.org>,
        Robin Murphy <robin.murphy@....com>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>
Cc:     linux-kernel@...r.kernel.org, linux-mediatek@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org,
        Fabien Parent <fparent@...libre.com>,
        Markus Schneider-Pargmann <msp@...libre.com>,
        Amjad Ouled-Ameur <aouledameur@...libre.com>,
        devicetree@...r.kernel.org, iommu@...ts.linux.dev
Subject: Re: [PATCH v2 2/3] iommu/mediatek: add support for 6-bit encoded port
 IDs

Il 04/10/22 12:01, Alexandre Mergnat ha scritto:
> From: Fabien Parent <fparent@...libre.com>
> 
> Until now the port ID was always encoded as a 5-bit data. On MT8365,
> the port ID is encoded as a 6-bit data. This requires to rework the
> macros F_MMU_INT_ID_LARB_ID, and F_MMU_INT_ID_PORT_ID in order
> to support 5-bit and 6-bit encoded port IDs.
> 
> Signed-off-by: Fabien Parent <fparent@...libre.com>
> Signed-off-by: Markus Schneider-Pargmann <msp@...libre.com>
> Signed-off-by: Alexandre Mergnat <amergnat@...libre.com>
> ---
>   drivers/iommu/mtk_iommu.c | 24 ++++++++++++++++++++----
>   1 file changed, 20 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/iommu/mtk_iommu.c b/drivers/iommu/mtk_iommu.c
> index 5a4e00e4bbbc..a57ce509c8b5 100644
> --- a/drivers/iommu/mtk_iommu.c
> +++ b/drivers/iommu/mtk_iommu.c
> @@ -108,8 +108,10 @@
>   #define F_MMU_INT_ID_SUB_COMM_ID(a)		(((a) >> 7) & 0x3)
>   #define F_MMU_INT_ID_COMM_ID_EXT(a)		(((a) >> 10) & 0x7)
>   #define F_MMU_INT_ID_SUB_COMM_ID_EXT(a)		(((a) >> 7) & 0x7)
> -#define F_MMU_INT_ID_LARB_ID(a)			(((a) >> 7) & 0x7)
> -#define F_MMU_INT_ID_PORT_ID(a)			(((a) >> 2) & 0x1f)
> +#define F_MMU_INT_ID_LARB_ID(a, int_id_port_width)	\
> +				((a) >> (((int_id_port_width) + 2) & 0x7))
> +#define F_MMU_INT_ID_PORT_ID(a, int_id_port_width)	\
> +				(((a) >> 2) & GENMASK((int_id_port_width) - 1, 0))

I can't think about any cleaner way than this one, but that's decreasing human
readability by "quite a bit".

The only way you can keep it readable is by adding a comment before these macros
that explains the sub-fields of FAULT_ID, located in the INT_ID register: please
add that.

Regards,
Angelo