linux-kernel - Re: [PATCH v2 4/7] iommu/exynos: Use lookup based approach to access registers

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Message-ID: <CAPLW+4ktP0_W_OgjAoK3BXOFaEiXvP1qNGCc-iQyr2fNL1srug@mail.gmail.com>
Date:   Thu, 14 Jul 2022 16:15:33 +0300
From:   Sam Protsenko <semen.protsenko@...aro.org>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
Cc:     Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>,
        Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
        Janghyuck Kim <janghyuck.kim@...sung.com>,
        Cho KyongHo <pullip.cho@...sung.com>,
        Daniel Mentz <danielmentz@...gle.com>,
        David Virag <virag.david003@...il.com>,
        Sumit Semwal <sumit.semwal@...aro.org>, iommu@...ts.linux.dev,
        linux-arm-kernel@...ts.infradead.org,
        linux-samsung-soc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 4/7] iommu/exynos: Use lookup based approach to access registers

On Tue, 12 Jul 2022 at 19:52, Krzysztof Kozlowski
<krzysztof.kozlowski@...aro.org> wrote:

[snip]

> > +static void sysmmu_write(struct sysmmu_drvdata *data, size_t idx, u32 val)
> > +{
> > +     writel(val, data->sfrbase + data->regs[idx]);
>
> Beside what Robin wrote, I also don't think these wrappers actually
> help, because you reverse arguments comparing to writel.
>
> How about having a per-variant structure with offsets and using it like:
>
> #define SYSMMU_REG(data, reg) ((data)->sfrbase + (data)->variant->reg)
> writel(CTRL_ENABLE, SYSMMU_REG(data, mmu_ctrl_reg))
>
> Would that be more readable?
>

Yes, this looks better for my taste too. I tend to get a tunnel vision
when working with downstream code for a while. But I noticed that that
approach is used sometimes as well, e.g. in
drivers/pinctrl/samsung/pinctrl-exynos-arm64.c (in struct
samsung_pin_bank_type). Anyway, I've reworked it exactly as you
suggested, will send v2 soon. Thanks!

>
> Best regards,
> Krzysztof