linux-kernel - Re: [PATCH] staging: fieldbus: anybuss: force address space conversion

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Message-ID: <CAGngYiU_iK5=swD_DA5PcOeYFT0zTrdQ+30Db0YrahuEukEP_A@mail.gmail.com>
Date:   Tue, 21 May 2019 11:53:15 -0400
From:   Sven Van Asbroeck <thesven73@...il.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     Dan Carpenter <dan.carpenter@...cle.com>,
        devel@...verdev.osuosl.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] staging: fieldbus: anybuss: force address space conversion

On Tue, May 21, 2019 at 11:42 AM Greg KH <gregkh@...uxfoundation.org> wrote:
>
> Ick, if you are using __force, almost always something is wrong.
>

What if I create a separate structure for the regmap context ?

struct anybus_regmap_context {
        void __iomem *base;
};

Then just store the base pointer inside the struct, and pass the struct
as the regmap context:

ctx = devm_kzalloc(dev, sizeof(*ctx), GFP_KERNEL);
ctx->base = base;
devm_regmap_init(..., ctx);

static int write_reg_bus(void *context, unsigned int reg,
                  unsigned int val)
{
        struct anybus_regmap_context *ctx = context;
        <now access ctx->base>
}

Penalty is an additional dynamic pointer-size
allocation. Pro: it'll be formally correct ?